Science for ICSE Schools Biology
8 Dr Srinivas Swamy Sanidhi
University Printing House, Cambridge CB2 8BS, United Kingdom One Liberty Plaza, 20th Floor, New York, NY 10006, USA 477 Williamstown Road, Port Melbourne, VIC 3207, Australia 314–321, 3rd Floor, Plot 3, Splendor Forum, Jasola District Centre, New Delhi – 110025, India 79 Anson Road, #06–04/06, Singapore 079906 Cambridge University Press is part of the University of Cambridge. It furthers the University’s mission by disseminating knowledge in the pursuit of education, learning and research at the highest international levels of excellence. www.cambridge.org Information on this title: www.cambridge.org/9781108593625 © Cambridge University Press 2018, 2019 This publication is in copyright. Subject to statutory exception and to the provisions of relevant collective licensing agreements, no reproduction of any part may take place without the written permission of Cambridge University Press. First published 2018 Second edition 2019 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 Printed in India by Nutech Print Services, New Delhi 110020 ISBN 978-1-108-59362-5 Cambridge University Press has no responsibility for the persistence or accuracy of URLs for external or third-party internet websites referred to in this publication, and does not guarantee that any content on such websites is, or will remain, accurate or appropriate. Information regarding prices, travel timetables, and other factual information given in this work is correct at the time of first printing but Cambridge University Press does not guarantee the accuracy of such information thereafter. notice to teachers
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Preface Science as a concept is an ever changing, expanding system of organised knowledge which grows relentlessly to encompass every facet of our life and beyond. A speck of scientific thought starts in an inquisitive mind which when couples with observational facts and logic, leads to discoveries. Our series Cambridge Connection: Science for ICSE Schools will enhance the spirit of scientific endeavours and handhold a young mind into the realm of science. The series is prepared in conformity with the latest syllabus prescribed by the Council for the Indian School Certificate Examinations. It will give students opportunities to construct knowledge through activities and projects, connecting new ideas to the existing ones thereby relating learning to the real world situations. Our objective is to make the learner become more reflective about their learning outcomes and how to solve pressing problems. The series will also evolve teachers from mere transmitters of knowledge to being a facilitator. They will get opportunities to nurture the metacognitive skills of their students through discussions and debates. A right blend of digital and print support will assist teachers to address the needs of different types of learners. Cambridge Connection: Science for ICSE Schools will thus, attempt to light up the journey of science.
–Author
Quick Check 2
cotyledons
About the Series Unisexual
Action Time
Chapter Objectives
Interesting activities to help in understanding the concepts
apter LearningChobjectives being covered Thesystem the Respiratory Flower 5 in the chapters
Bisexual
Using the Internet, give two examples each of unisexual and bisexual flowers. Why do you think we should not pluck flowers?
ACTION TIME
1
The seed Kundan often feels nervous during his examinations. His teacher suggested that he should take deep breaths to overcome his nervousness. How do you think deep breathing helps? Discuss. •
RespiRation in Human Beings
•
B. Give Reasons.
Quick Check
C.
2
ACTION TIME
3
The bean seed (Dicot
Info Hub
C. Question and Answers.
Questions to encourage Respiration self-learning and assessment Tooth decay
ACTION TIME
Role Play:
Interesting facts related to the concept
Subject Connect
INFO HUB
•
•
•
Quick Check 1 and guess the term related to it. D. Read the feature/characteristic
Fig. 5.1 Respiratory system in human beings
Cross-Pollination
Structure of a seed
Life Connect
D. Discuss:
Tongue
E.
III. Long Answer Questions.
Care of teeth
Agents of Pollination
Info Gathering:
breathing s C I E N T I F I C q U E s T
Challenge
Scientific Quest
FunCTions oF A Flower
Out-of-the-box thinking questions
Insect pollination or Entomophily
pollination
IV. Challenge
• •
INFO HUB
Pollination
Projects based on topic
Life Connect
• •
ACTION TIME
2
Fig. 4.4 Correct way of using the floss.
Teaching Tips
Fig. 2.2 Pollination in flowers
Key Terms
Self-Pollination
Saliva
Cues for the teacher for an exciting and fun-filled class
Definition of the scientific terms that are used in the chapter Fig. 4.5 Parts of the mouth
k E y T E rM s Cell sap:
q U I C k NOT E s E N j Oy s C I E N C E
✶♦ ✶♦ ✶♦ ✶♦ ✶♦ ✶♦ ✶♦ ✶♦
P I C T Ur E s Ur V E y Larynx
Nostrils Trachea
Enjoy Science Learning through fun activities, puzzles, crosswords
Fig. 2.10 Structure
Picture Survey
Run-Through
ACTION TIME
q U I C k NOT E s ✶♦ ✶♦ ✶♦
II. ✶♦
2
Supports learning through picture-based questions/activities
Complete revision of the chapter through Answer Questions. exercises Short well-planned
A. Give reasons. ✶♦
P I C T Ur E s Ur V E y
rUN-THrOUgH ions. Very Short Answer Quest t answer. A. Tick (✓) the correc
I.
B. Question and answers.
k E y T E rM s Unicellular organisms: Multicellular organisms: Cell sap: Cristae:
III. Long Answer Questions.
Quick Notes follow B. State whether the statements.
IV. Challenge Enrichment
Summarising the chapter
ct the false
or False. Corre ing statements are True
Extends learning beyond the book V.
q U I C k NOT E s ✶♦ ✶♦ ✶♦ ✶♦ ✶♦ ✶♦ ✶♦ ✶♦
Enrichment
Case Study
A. Discuss: B.
Real-life situations, designed to help the students to find solutions to tasks, and help in decision making
C. Info Gathering:
r A P I D F I r E 1
Rapid Fire
Complete the crossword.
c a s e s tu dy 2
Quick revision through objective-type questions
Across
Down
Practice Test Paper Assignments to assist students to practice concepts
practice Test paper 2 I.
Tick (✓) the correct option.
Tasks for the student to recapitulate and learn something new II. Match the following:
A to Z Task
Logical Reasoning To judge student’s ability to reason out correctly
III. Read the clues and answer in one word.
Life Connect Links Science to real-life situations
A to Z Task
Subject Connect Links Science to other subjects
IV. Answer the following questions.
Contents 1. Transport of Food and Minerals in Plants 1 2. Reproduction in Plants and Animals 17 Rapid Fire 1
39
3. Ecosystems 40 Rapid Fire 2
58
Practice Test Paper 1
59
4. Human Body
60
5. Health and Hygiene
85
Rapid Fire 3
104
6. Food Production
105
Rapid Fire 4
129
Practice Test Paper 2
130
Logical-Reasoning
131
Case Study 1
132
Case Study 2
133
A to Z Task
134
Transport of Food and Minerals in Plants
Chapter
1
Chapter Objectives In this chapter, you will learn about: ♦♦ Absorption of water by roots ♦♦ Absorption of mineral salts by roots ♦♦ Osmosis and diffusion
♦♦ Root pressure ♦♦ Mechanism of transpiration and its significance ♦♦ Translocation
What will happen if plants and animals do not get water for a few days? Discuss.
Introduction Plants obtain energy from food to perform their daily vital activities. They obtain their own food by the process of photosynthesis in the presence of sunlight and chlorophyll by taking in minerals and water from the soil and carbon dioxide from the air. The end products of the process include glucose and oxygen.
other parts. Thus, there are mainly two types of conduction processes in plants:
1. One that carries water and minerals from roots to other parts. 2. One that carries food prepared in leaves to other parts.
In this chapter, we will discuss about transport Transportation is a process in which a substance process in plants. absorbed or produced in one part is taken to
Absorption of water by Roots Glucose moves up to the growing bud
Bud
Water and minerals from soil
Leaf
Stem
Soil
Glucose made by photosynthesis
Glucose moves down to the growing root
Water and minerals are taken up by roots
Fig. 1.1 Transportation of substances in plants (Diagrammatic representation)
Plants can absorb water through their entire surface. However, since water is mainly available in soil, a well-developed root system is present to absorb water. Other functions performed by roots are: • Anchorage of plant to the soil.
• Site of storage of food and other nutrients.
Water is an important component for a plant. It plays a signif icant role in:
• Carrying out various life processes such as photosynthesis and transpiration. • Absorbing minerals from the soil.
1
Structure and Speciality of Root Hair
increases, the surface area also increases, and the Root is covered at the tip by root cap, which plants absorb more water and minerals. protects the delicate apex behind the cap as Osmosis the root invades deep in soil. Roots are covered Osmosis is a distinct type of transmission of by a single-celled layer called epidermis. water that occurs through a semipermeable The epidermal cells have f inger-like tubular ined as the movement of membrane. It is def outgrowth known as root hair that aid in water (or solvent) across semipermeable membrane increasing the surface area for absorption of from a region of its high concentration to a region water. of its low concentration. The concentration of As the plants grow, their roots branch and water is higher in soil, thus water moves from rebranch and get f ixed in the soil. At the tips of soil (higher concentration) to root cells (lower roots, a large number of cells absorb water and concentration) through plasma membrane. nutrients from the soil. These Salt Water cells have a semipermeable plasma membrane. Plasma membrane has tiny pores that Roots allow only selected materials and water molecules to pass through it by a process known as osmosis. The amount of Fig. 1.3 Movement of molecules across water absorbed is proportional semipermeable membrane in plants to the number of root hair. Fig. 1.2 Roots in plants As the number of root hair ACTION TIME
1
Activity: To study the transportation process and functioning of cells in a potato. Procedure: • Peel a potato, cut it into two pieces and slice its bottom part. • Make a deep hole on the top part of the potato and make a potato cup. • Put some sugar solution in the cup. • Make a note of the level of the sugar solution.
Sugar Solution
• Pierce the outer wall of the potato with a pin. • Place the potato in a container with water in such a way that it is partly immersed in water. Leave it undisturbed for some time. Observation: The level of the sugar solution increases.
Water
Conclusion: This is because water moves from glass beaker (lower concentration) to potato (higher concentration), through a selectively permeable membrane. Thus, the process of osmosis has taken place.
2
Teaching Tip: The meaning of surface tension can be explained to students. (Surface tension is the energy, or work, required to increase the surface area of a liquid due to intermolecular forces.)
Diffusion
Diffusion is a process of movement of molecules from a region of higher concentration to a region of lower concentration. Active Transport
ined as the transport of Active transport is def substances across the cell membrane against the concentration gradient. It requires input of energy and does not take place impulsively. The transport of substances takes place from low concentration to high concentration, or uphill transport across the cell membrane. The energy is usually obtained from respiring root cells. Active transport is unidirectional and the transport always takes place through carrier proteins present in the membrane. Concentration gradient
Carrier protein Outside cell Cell membrane
Inside cell
Fig. 1.4 Movement of molecules by active transport
Quick Check 1 A. Fill in the blanks. 1. The process of preparation of food by plants in the presence of light is called ............................ (photosynthesis/ transpiration). 2. ............................ (Osmosis/Diffusion) occurs through a semipermeable membrane. 3. Root hair increase the ............................. (anchorage/surface area) for absorption.
4. Osmosis involves movement of water across ............................. (semipermeable/ permeable) membrane. 5. ............................. (Diffusion/Osmosis) is movement of substances from high to low concentration. 6. Active transport takes place through carrier .............................. (seats/proteins).
Conducting Tissue A tissue is a group of cells that performs a specialised function in organisms. These are commonly known as conducting tissues. The conducting tissues are of two types. They are xylem and phloem. The xylem carries water and nutrient minerals from the roots to the leaves. The phloem carries food from leaves to various parts of the plant. INFO HUB Water does not travel through xylem vessels by osmosis. Osmosis involves the movement of water across cell membranes. Xylem cells do not have any living contents when mature, so there will be no membrane.
Capillary action pulls water from the roots to the leaves. On absorption, water moves from the outer layer of the epidermis to the specialised tissue called xylem. Xylem are pipe-like vessels in plants through which water and minerals enter. Each vessel is made up of thick walls and elongated cells. These tissues form a continuous network within the plants, and spread across the roots, stem, branches and leaves. Thus, water and dissolved minerals are transported in the form of sap. The sap moves in an upward direction against the gravity to reach the leaves of the plant. This upward movement of sap (from the root to the crown) is called ascent of sap (Fig. 1.5). It is aided by transpiration and root pressure.
Teaching Tip: Active transport can be demonstrated using a video. Students can be asked to work in groups and design a model on it. | Concentration gradient: Fall in concentration
3
The root pressure pushes the water up towards the stem. The capillary action then further pushes the water up the narrow tubes of xylem. This rising of water through the narrow tubes of the xylem is called capillary action. The factors that are responsible for ascent of sap are: 1. Cohesion: It is the mutual attraction between water molecules. 2. Adhesion: It involves attraction of water molecules to the surface (surface of elements of xylem). TRANSPIRATION Xylem sap
Water molecules Atmosphere
Ascent of Sap
Xylem cells
Adhesion
Cohesion, Adhesion in the xylem
Cell wall
Cohesion by hydrogen bonding Water molecule Root Soil Water
Water uptake from soil
INFO HUB Cohesive and adhesive properties of water molecules help to form an unbroken continuous water column in the xylem.
Fig. 1.5  Ascent of sap
4
Teaching Tip: Hydrogen bonding can be briefly explained to students. | Capillary action: The tendency of a liquid in a capillary tube or absorbent material to rise or fall as a result of surface tension
Quick Check 2 Match the following: Column A 1. Tissue 2. Xylem 3. Phloem 4. Capillary action 5. Ascent of sap
Column B a. Pulls water from roots b. Carries food from leaves to other parts c. Carries water from roots to leaves d. Upward movement of water and minerals from the root to the crown e. Group of cells
INFO HUB Water potential of root cell is less than that of outside soil which causes movement of water into the root through osmosis. This results in root pressure which pushes water up the xylem.
Cuticular transpiration Cuticle is the multilayered waxy deposit that generally covers the leaves of the plants. Even though it is impermeable to water, but certain amount of water can pass through it. The amount of water lost depends on the thickness of cuticle.
Transpiration
Cuticle
Loss of water from the plant in the form of water vapour is known as transpiration. Based on the region from which it is taking place, it can be of following types—Lenticular, Cuticular and Stomatal.
Upper epidermis Palisade cells Spongy cells Xylem
Lenticular transpiration
Phloem Lower epidermis
Lenticels are small openings in the bark of young branches, cork of woody stems and fruits. Very small amount of water is lost through the lenticels.
Fig. 1.7 Leaf anatomy
INFO HUB
Lenticel
In dry conditions when the stomata of leaves with thin cuticle close, cuticular transpiration becomes significant.
Stomatal Transpiration
Cross-section of a stem showing lenticels Fig. 1.6 Lenticular transpiration
Transpiration mainly takes place through the stomata (singular, stoma) which are minute pores present in the leaves. Each stoma is surrounded by two bean-shaped guard cells.
Water potential: The energy required, per quantity of water, to transport infinitesimal quantity of water from the sample to a reference part of pure free water
5
The main function of stomata is to allow system of the plant is removed and its pot carbon dioxide to enter into the leaves for is covered with the polythene bag. The photosynthesis. It simultaneously functions presence of water droplets on the inner side to prevent excessive water loss. Loss of water of jar A after some time shows transpiration vapour through stomata is known as stomatal occurring from leaves. transpiration. Maximum amount of transpiration 2. Cobalt chloride: Two strips of f ilter paper in a plant body occurs through stomata. are soaked in 2 % solution of cobalt chloride and are perfectly dried under sunlight. Guard cells Cobalt chloride paper is blue in colour when it is dry, and becomes pink when it absorbs moisture. Due to this characteristic Stomata feature, it acts as a chemical indicator in this Chloroplast experiment. This method is used to compare the rate of transpiration between the two surfaces of a. Open stoma b. Closed stoma the same leaf suggesting that more stomata Fig. 1.8 Open and close of stomata in plants are present in the lower surface of the leaf. Experiments for Demonstrating Transpiration In this method, a piece of dry blue cobalt chloride paper is kept on a leaf. It is covered Transpiration can be demonstrated by the by glass slides with clips. The colour of cobalt following methods: chloride changing from blue to pink shows 1. Polythene bag: The process of transpiration transpiration. The time taken for this change can be demonstrated by covering a welldetermines the rate of transpiration. watered potted plant with a polythene bag Cobalt chloride paper and f irmly tying the knot at the mouth Rubber (on upper surface) band to prevent any water loss from the plant. The setup is kept in a bell jar in sunlight. Label this as jar ‘A’. A control experiment Leaf on Paper Cobalt Paper (turned a potted is done simultaneously in which the shoot (turned Glass chloride paper After placing the bell jars in sunlight for 1 hour Control Bell jars
A
B
Fig. 1.9 Release of water vapour by plants
6
slides
(on lower surface)
less pink)
more pink)
Fig. 1.10 Cobalt chloride turns pink to show that transpiration takes place
INFO HUB
Potted plant Polythene bags
plant
The colour change on the lower surface of the leaf is faster than on the upper surface as, generally, there is more number of stomata on the lower surface than on the upper surface.
Factors Affecting Transpiration
Importance of Transpiration
The rate of transpiration is affected by several 1. Transpiration directly stimulates the external and internal factors. Temperature, light, absorption of water from the soil and humidity, wind speed and availability of water exerts a negative pressure (tension) which in soil are the f ive external factors on which the pulls water upwards in xylem. This is called rate of transpiration depends. transpirational pull.
1. Temperature: The rate of transpiration 2. It regulates the temperature of the plant increases with increase in temperature. High body. The temperature of the plant rises temperature favours evaporation of water as it absorbs energy from the Sun for from the leaves. photosynthesis. Evaporation of water from the plant body helps in getting rid of the 2. Light: Stomata remain open during day excess heat energy, thus preventing heat time, hence most of the transpiration takes injury of the leaves. place during the day. At night, the stomata
remain closed, so very little amount of 3. It helps in absorption and transportation of water is lost by cuticular or lenticular minerals to all parts of the plant body, and transpiration. If the intensity of light is thus helps in the growth and development of high and it is provided for a longer duration, the plant. then the temperature of the surrounding 4. When cells absorb water, they remain turgid. increases as a result of which transpiration This helps in maintaining the shape and also increases. structure of the plant body. 3. Humidity: The actual water content of air is known as humidity, which is expressed as Guttation vapour pressure. The difference in vapour During the periods of low evaporation such pressure between the atmosphere and as early morning or at night, water droplets the intercellular spaces of the leaf affects can be observed around special vein openings transpiration. With increase in humidity, (hydathodes). During such periods, root transpiration decreases. If the humidity is low, pressure is very high, thus water is forced up to that is, vapour pressure in the surrounding the xylem and comes out of the plant body. This atmosphere is low, the transpiration is is the excess water that is collected. This loss of favoured. water in the liquid state is known as guttation.
4. Wind speed: Increase in wind speed increases the rate of transpiration. 5. Availability of water in soil: If less water is available in the soil, the rate of transpiration decreases; as a result, the stomata will be partially or completely closed.
Fig. 1.11 Loss of water by plants through guttation Turgid: Abnormally distended especially by fluid or gas
7
Quick Check 3 State whether the following statements are True or False. 1. Cuticles are small openings in the bark of young branches. 2. Cuticular transpiration is significant in dry conditions. 3. Maximum amount of transpiration occurs through lenticels. 4. Each stoma is surrounded by two guard cells. 5. Main function of stomata is transpiration. 6. In the bell jar experiment, the potted plant is covered with polythene bag to prevent loss of water. 7. The colour of cobalt chloride changes from pink to blue shows transpiration. 8. Rate of transpiration increases with increase in temperature. 9. Stomata remain closed during day time to prevent water loss. 10. Increase in wind speed decreases transpiration. 11. Transpiration is favoured when humidity is low. 12. Loss of water in liquid form is called guttation.
Transport of Food and Other Substances Plants use carbon dioxide and water to prepare glucose and oxygen in the presence of sunlight by the process known as photosynthesis. Once the food is produced in the leaves, it is required to be circulated to the entire plant body so that the glucose can be used by each cell to obtain energy by respiration. Sunlight + Water +
Glucose (Carbohydrates)
Carbon dioxide + Oxygen
Write the balanced chemical equation for photosynthesis. .............................................................................
The glucose is manufactured mainly in the palisade cells of leaves and then it is passed to the phloem which carries it to other parts of the plant. Transport of food materials from leaves to other parts of the plant is called translocation. The food can be stored in roots, stems or fruits. 8
Sieve plate (End wall) Sieve tube Companion cell Fig. 1.12 Transport of food through phloem in plants
Phloem tissue is made up of different types of cells; two of them are: 1. Sieve tubes 2. Companion cells A continuous column from the leaves to other parts of the plant is formed by the arrangement of cylindrical cells, called sieve tubes, one above the other. It has sieve-like partitions at both ends. These partitions are called sieve plates. The companion cells are found next to the sieve cells, that assist the sieve tubes to function properly.
Transpiration of water Companion cell
Water
Source (Leaf cell)
Sucrose
Sieve tube elements
Translocation of sucrose
then answer the questions that follow. The results for the two plants were recorded in the following table. Time of day Water loss in plant A (ml) Water loss in plant B (ml)
3h 0.0
6h 1.6
0.2
4.0
9 h 12 h 9.0 7.6 19.0
17.7
1. From which plant was the greatest amount of water loss recorded? 2. Which time of day was the greatest water loss recorded for both plants A and B? Why do you think this is so?
Importance of Minerals Water Companion cell a. Xylem
Sink (Root cell)
b. Phloem
Fig. 1.13 Transport of materials in plants through xylem and phloem
INFO HUB Applied chemicals, such as pesticides, also move through the plant by translocation.
ACTION TIME
2
Aim: To check transport of materials in a plant. Procedure 1: Cut the flower stalk of a white flower lengthwise. Place each segment of stalk in a different-coloured dye. Predict how the colours might move up the stalk and into the flower. Leave for a few hours and observe the changes. Explain the reason for colour change. Procedure 2: The water loss in two plants was recorded over a 12-hour period. Study the information and
Plants need a number of minerals for healthy growth. These are absorbed through the roots as mineral ions dissolved in the soil water. The minerals (nutrient elements) required by the plants are divided into two categories— micronutrients and macronutrients. Micronutrients are the essential elements that are required in extremely small quantities by the plants. They include boron (B), copper (Cu), iron (Fe), manganese (Mn), molybdenum (Mo), zinc (Zn), nickel (Ni) and chloride (Cl). For example, the presence of copper is closely linked to vitamin A production, and it helps ensure successful protein synthesis. Iron (Fe) is essential for crop growth and food production. Manganese (Mn) activates several important metabolic reactions and plays a direct role in photosynthesis. Zinc is a part of plant’s enzymes. Macronutrients are the essential elements that are required in large quantities by the plants. They play an important role in balanced crop nutrition. They include nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), sulphur (S), 9
magnesium (Mg), etc. NPK salts are very important for the plant growth. For example, nitrogen is required for protein formation, phosphorus for production of energy, and potassium regulates the opening and closing of stomata. Magnesium is a constituent of the chlorophyll molecule. As a carrier, it is
also involved in numerous enzyme reactions as an effective activator, in which it is closely associated with energy-supplying phosphorus compounds. Lack of nutrient elements can lead to def iciencies (Table 1.1).
Table 1.1 Deficiencies due to lack of some nutrient elements
Iron Manganese Zinc Nitrogen Phosphorus Potassium
Micronutrients Yellowing of leaves (chlorosis) Yellowing of leaves with grey spots (chlorosis) Malformed leaves, yellowing of leaves, stunted plant growth Macronutrients Yellowing of leaves, retarded growth, wrinkling of cereal grains Delay in seed germination, poor root growth, purple and red spots on leaves Poor and stunted growth
Quick Check 4 A. State whether the following statements are True or False. 1. Phloem transport is bidirectional. 2. Glucose is required by every cell for respiration. 3. Food can be stored only in leaves. 4. Plant requires only water for photosynthesis. 5. Sieve tubes assist companion cells. B. Fill in the blanks. 1. ............................. (Sieve tubes/Stomata) form a continuous column from leaves to other parts of plants. 2. Glucose is formed in ............................. (palisade/cuticular) cells of leaves. 3. Transport of food from leaves to other parts of leaves is called .............................. (transpiration/ translocation). 4. Phloem tissue is made up of ............................. and .............................. (sieve tubes/xylem cells/ companion cells). 5. Nitrogen is a ............................. (micronutrient/macronutrient) for plants. 6. The loss of water in liquid state is called ............................. (hydathodes/guttation).
10
k e y T e rm s Diffusion: The movement of fluid from the region of higher concentration to the region of lower concentration (without using energy) Osmosis: The diffusion of water (or solvent) across semipermeable membrane from a region of its high concentration to a region of its low concentration Active transport: The transport of substances across the cell membrane against concentration gradient with the input of energy Sap: Water and dissolved minerals that are conducted by a plant Ascent of sap: Upward movement of water from the xylem to other parts of the plant Root pressure: The pressure that develops in xylem vessels as a result of metabolic activity of roots Transpiration: The process that causes a loss of water in the form of water vapour through the aerial parts of a plant Cuticle: The multilayered waxy deposit that generally covers the leaves of the plants and is mostly impermeable to water Guard cells: Specialised cells which guard each stomatal pore and function as valves, and regulate the size of the pore Transpirational pull: The tension in the water column of xylem created by transpiration which causes water to move up the plant as it is pulled through the plant body Stomata: The small pores found on the epidermis of leaves and other soft aerial parts Hydathodes: Vein openings or pores found along the leaf margins mainly responsible for guttation Guttation: The process in which excess water is lost in the form of liquid droplets along the margins of leaves through hydathodes (vein openings) Translocation: The movement of food materials from leaves to other parts of the plant
q u i c k not e s ✶✶ Plants have a transport system made up of xylem and phloem. ✶✶ The xylem carries water and minerals from the soil to the leaves of the plant. ✶✶ The phloem carries dissolved food from the leaves to various parts of the plant. ✶✶ Osmosis is a special kind of diffusion of molecules through a semipermeable membrane. ✶✶ Ascent of sap is the flow of water and minerals from roots to the aerial parts of a plant. It takes place
due to transpirational pull. ✶✶ The factors responsible for ascent of sap are adhesion and cohesion. ✶✶ Based on the region from which transpiration is taking place, it can be of following types—lenticular,
cuticular and stomatal. ✶✶ The factors affecting transpiration are—temperature, light, humidity, wind speed and availability of
water in soil. ✶✶ Plants need a number of minerals for healthy growth. These minerals can be—micronutrients and
macronutrients.
11
run-through I. Very Short Answer Questions. A. Tick (✓) the correct option. 1. Rate of transpiration slows down when plant: a. straightens
b. wilts
c. grows
d. none of these
c. companion
d. supportive
2. Phloem tissue contains ............................ cells. a. component
b. colleague
3. Food is carried away from leaves to other parts of plant by these cells: a. Dead cells of xylem
b. Companion cells and sieve tubes of xylem
c. Companion cells and sieve tubes of phloem
d. Root pressure in xylem
4. Which of the following is not present in NPK salts? a. Nitrogen
b. Sulphur
c. Potassium
d. Phosphorus
5. Which one of the following favours the fastest transpiration rate? a. A cool humid, windy day
b. A hot, humid, windy day
c. A hot, humid, still day
d. A hot, dry, windy day
6. When temperature of surroundings increases, rate of transpiration ............................ . a. increases
b. decreases
c. remains same
d. may increase or decrease
7. When photosynthesis is faster than the rate of respiration, oxygen gas is ............................ . a. exchanged
b. taken in
c. given out
d. transferred to roots
8. Carbon dioxide and oxygen move in plants by the process of ............................ . a. xylem
b. phloem
c. diffusion
d. stomata
9. In bigger trees, gases pass through small openings in bark known as ......................... . a. cuticles
b. lenticels
c. stomata
d. hard pores
10. Which of the following is/are conducting tissue/s in plants? a. Xylem
b. Phloem
c. Both (a) and (b)
d. None of these
11. Xylem is a vessel in plants, responsible for transporting: a. Water and minerals to leaves from roots
b. Food and minerals to roots from leaves
c. Prepared food to other parts from roots
d. Prepared food to other parts from leaves
12. Water evaporates from tiny pores from under the leaf. These pores are known as ........................... . a. cuticles
b. lenticels
c. epidermis
d. stomata
B. Fill in the blanks. 1. Water reaches at top of plant because of suction pull created by .................................... (photosynthesis/transpiration). 2. Special vein openings in plants are known as .................................... (stomata/hydathodes).
12
3. Rate of transpiration .................................... (increases/decreases) when wind is humid. 4. Stomata remains closed .................................... (during the day/at night). 5. .................................... (Wind speed/Transpiration) causes cooling of leaves.
C. Match the following: Column A
Column B
1. Humidity
a. Photosynthesis
2. Chlorophyll
b. Decreases transpiration
3. Ascent of sap
c. Increases transpiration
4. Osmosis
d. Semipermeable membrane e. Cohesion, Adhesion
D. State whether the following statements are True or False. 1. Transpiration increases the temperature of a plant. 2. Water enters the root hair by diffusion. 3. The structure of root hair is suitable for absorbing water from the soil. 4. Water is required by leaves for photosynthesis. 5. Phloem transports minerals from roots to leaves.
E. Answer the following in one word. 1. Tissues that cause transportation of water:
...................................
2. Dead tissues that carry food:
...................................
3. Part of root that absorbs water:
...................................
4. Process of evaporation of water from leaves:
...................................
5. Pigment present in leaves that traps sunlight:
...................................
F. Define the following terms. 1. Semipermeable membrane
2. Ascent of sap
3. Transportation
4. Root hair
5. Transpiration
II. Short Answer Questions. A. Differentiate between: 1. Diffusion and Osmosis 2. Xylem and Phloem 3. Micronutrients and Macronutrients 4. Transpiration and Guttation 5. Stomata and Lenticels
13
B. Answer the following questions. 1. Why is transport of materials necessary in a plant? 2. What are xylem and phloem made up of? 3. Under what circumstances do the plants transpire slowly? 4. How are roots useful to the plants? 5. What are the different types of transpiration? 6. How do root hair increase the surface area for absorption? 7. When does active transport occur in a cell? 8. Are xylem cells living or dead? 9. How does ascent of sap occur against gravity? 10. How is guttation different from transpiration? 11. Why is transpiration important for plants? 12. How do guard cells cause closing and opening of stomata? 13. How are nutrient elements important for plants?
III. Long Answer Questions. 1. Describe the usefulness of transpiration for plants. 2. Explicate three methods that make transpiration to occur in plants. 3. Explain how water is absorbed by the roots and transported to other parts of the plants. 4. Briefly explain the factors that affect the rate of transpiration. 5. Roots and leaves are essential for each other. Explain how. 6. Diffusion is passive transport. Explain. 7. Explain the transport of materials through xylem and phloem in plants. Support with a labelled diagram.
IV. Challenge Life Connect
On a hot day, in the middle of a drought, how do you expect the leaves of a plant to look like? Draw a diagram to describe your answer.
V. Enrichment A. Activity: Get vegetables like lady’s fingers, brinjals, tomatoes and beans from Life Connect
14
the market which are dry and shrivelled up. Put them in a bowl of water for some time. What do you notice? The vegetables start looking fresh again. There is movement of water in the vegetables through the semipermeable membrane from higher water concentration to lower water concentration, which is called osmosis. Due to this the vegetables swell up and look fresh.
Explicate: Make plain and comprehensible
B. Know Your Scientist—Jagdish Chandra Bose (1858–1937)
Life Connect
Sir Jagdish Chandra Bose is one of the most prominent first Indian scientists who proved with his experiments that both animals and plants share much in common. He proved that like animals, plants are also sensitive to heat, cold, light, noise and various other external stimuli. He manufactured a very sophisticated instrument called Crescograph that could record and observe the minute responses of plants to external stimulus. It was capable of magnifying the motion of plant tissues to about 10,000 times of their actual size, which found many similarities between plants and other living organisms.
C. Activity: Select a potted plant and cut a small part of its branch with a razor. Leave the branch for one week. Write your observations. Conclusion: You will find that part of the stem over the cut portion is swollen up. While the lower part of the plant stem remains unchanged. This is because the food prepared by the leaves could not be carried below the cut part of the stem. The food gets collected on the upper part, so the stem swells up.
D. Activity Time!
Aim: To observe transport of water through the stem.
Take two similar white flowers, for example, white rose, carnation, balsam or Petunia. Cut off the long stem to make them short. Dissolve red ink and blue ink in water in two separate transparent glasses. Keep the flowers with the stems dipped in the glasses. Wait for 6–7 hours. Do you notice any change in the colour of the flower? Note down your observations. How does this happen?
S c i e n t i f i c Q u e s t 1. Transpiration—can plants do without it? It is estimated that 98% of a plant’s energy is used in the work of transpiration. It is an important process for the well-being of plants. How? Search the Internet and have a class discussion. Write a 200-word report in your notebook. 2. How are conducting tissues in microscopic plants such as Chlamydomonas and Spirogyra different from those in higher plants such as Petunia and mango tree? Find out using the Internet and the school library. Make a two-page report in your notebook.
e n j oy s c i e n c e 1. Make a crossword using the following words. Also, write the clues in your notebook. GUTTATION
ADHESION
HUMIDITY
SIEVE PLATE
TRANSLOCATION
CUTICLE
2. Make a concept map on ‘Types of Transpiration’.
15
P I C T UR E S UR V E Y Look at the figure and answer the questions that follow.
C
Root hair B
A
Water entering root hair Xylem
Phloem
Cortex
Piliferous layer
A section of root to show path of water through it
1. What does the above figure depict? 2. What processes are involved in it? 3. Which tissues are involved in it?
16
Piliferous layer: The part of the root epidermis that bears root hairs
Chapter
2
Reproduction in Plants and Animals
Chapter Objectives In this chapter, you will learn about: ♦♦ Modes of reproduction ♦♦ Asexual reproduction ♦♦ Tissue culture
♦♦ Sexual reproduction in plants ♦♦ Sexual reproduction in human beings
What will happen if organisms do not reproduce? Have a class discussion.
Introduction
Modes of Reproduction
All living beings exhibit the basic characteristics that are important for their survival and growth. Among other things, living beings need to reproduce, so that their species survive. Thus, reproduction can be defined as the process of living beings producing young ones of their own kind. Just like a seedling turns into a plant when it grows, likewise, a small pup grows into a dog. Living organisms reproduce to maintain their number and also for the continuation of their species. All species reproduce in different ways. For example, animals such as dogs and cats give birth to young ones, whereas birds lay eggs. The animals that give birth to their young ones are called mammals.
There are two modes of reproduction—Sexual Reproduction and Asexual (Vegetative) Reproduction.
a. A hen lays eggs b. A cat gives birth to young ones Fig. 2.1 Reproduction in animals
Why do birds lay eggs in nests? .............................................................................
• Sexual Reproduction: In this method of reproduction, both the male and female parents are involved. Both the parents have reproductive organs. Male and female gametes fuse to form a zygote. This zygote develops into a new individual. For example, humans, dogs and cats reproduce by sexual reproduction. • Asexual Reproduction: In this method of reproduction, a single parent gives rise to the new individual. It does not involve the fusion of male and female gametes. The offspring produced by this method are the exact copies of their parent. Amoeba, Hydra and yeast are some lower organisms that reproduce by asexual reproduction.
Asexual Reproduction in Plants In asexual method of reproduction, some plant parts including the stem, root and leaves help in developing new plants. Reproduction can also 17
take place by formation of spores in certain plants. Budding Other methods of asexual reproduction include In this method, a small bud-like outgrowth binary f ission, budding, fragmentation, etc. is seen in the parent body. This bud grows, continues to increase in size and eventually gets Binary Fission detached from the parent. It may also happen Small and lower organisms such as bacteria, that the bud grows and forms one whole body Paramecium and blue-green algae reproduce and again grows a bud, thereby leading to a through the method of binary f ission. Here, chain of buds. During the growing phase of the the word ‘binary’ means ‘two’ and ‘f ission’ means bud, the nucleus within the parent cell divides ‘splitting’. In this method, the nucleus f irst splits into two. One part moves into the bud and as a into two and thereby, leads to the splitting up of result, the detached bud is capable of growing the whole cell which f inally forms two identical into an independent plant. Reproduction by the twin cells, called the daughter cells. method of budding is commonly seen in yeast. Daughter Nucleus nucleus
Bud
Daughter yeast
Nucleus Parent yeast Vacuole Daughter cells Fig. 2.2 Binary fission
Spore Formation Plants such as ferns, fungi and mosses reproduce by means of spores. The formation of spores is seen on the underside of the leaves of some ornamental plants. These spores can be compared to the seeds formed in higher plants. Spores are light, f loat in water and can also be dispersed easily by wind. They can survive for long period of time. Under suitable conditions, spores are capable of producing new plants.
Fig. 2.4 Budding in yeast
Fragmentation In this method of asexual reproduction, the parent plant divides into two or more parts or fragments. Each part or fragment then grows further into an independent new plant.The most common example of this kind of reproduction is seen in long f ilamentous or ribbon-like structures that are present in Spirogyra. Nucleus Septa
Sori
Fig. 2.3 Spore formation in a plant
18
Spiral chloroplast
Fig. 2.5 Fragmentation in Spirogyra
Fragment: A piece broken off or separated from something | Ornamental: Serving as aesthetic rather than a useful purpose
Vegetative Propagation
There are various ways of vegetative propagation in plants. The lower plants follow the method of budding or fragmentation. The higher plants reproduce or multiply by using the parts such as roots, stems or leaves. In vegetative propagation, plants reproduce from the vegetative parts such as roots, stems and leaves. Let us understand these methods one by one.
and falls off and develops roots while growing into a new plant. The offset is smaller in size and thicker than a runner. Water hyacinth and Pistia are examples of plants that reproduce by formation of offset.
Reproduction by stems
The stems that are involved in vegetative propagation are of two kinds—sub-aerial and underground. Sub-aerial Stems These stems are of three kinds, depending on how they grow.
• Runners and stolons: Runners and stolons are stems that grow parallel to the ground and produce a new plant at the node. The new plant formed may get detached from the stem and grow independently. Examples of plants that display such stems include strawberry, jasmine and mint. Runners and stolons are similar in the sense that they are both stems that grow horizontally. The main point of difference is that runners are usually straight while stolons are slightly arched.
Offset Roots
Fig. 2.7 Pistia reproducing through offset
• Suckers: Suckers are horizontal stems that develop from the base of the stem and then come out of the soil to form the shoot. This shoot can grow independently into a new plant when the horizontal stem breaks off. An example of sucker is Chrysanthemum. Main shoot Suckers
New shoot
Roots of new plant Adventitious roots Fig. 2.8 Chrysanthemum (guldaudi)
Underground Stems Main plant body Stolon Runner
New plantlet
Corm, rhizome, bulbs and tubers are the various kinds of underground stems.
• Corm: Corm is an underground stem that grows in clusters and is usually round in shape. Roots develop from the base and sides of the corm. Fig. 2.6 Runners and stolons in strawberry The examples of plants where corm is seen are • Offset: Offset is a side shoot that arises from a bud Gladiolus and saffron. present on the main stem. This bud usually detaches Root
New roots
19
• After a few days, you will observe that buds are growing into new aerial shoots to form a new plant. • Look at the roots of the plant now.
Fig. 2.9 Corm in Gladiolus
Observation: In ginger, buds grow into new plants and this type of stem modification is called rhizome.
• Bulbs: Bulbs are f leshy, short, vertically growing short stems. A bulb is surrounded by scale leaves that are f leshy, since they store food. Onion, garlic and lilies are examples of plants where bulbs are present. Fig. 2.10 Corm in saffron
• Rhizome: Rhizome is an underground stem that bears roots and shoots at the nodes. The roots and shoots develop into a new plant. Some examples of plants where rhizome is seen are grasses, canna, ginger and turmeric. Fig. 2.12 Onion is an example of a plant that reproduces by bulbs
ACTION TIME
2
Aim: To observe vegetative reproduction in onion through onion bulbs. Fig. 2.11 Turmeric is an example of a rhizome
ACTION TIME
1
Aim: To observe vegetative reproduction through rhizome. Procedure: • Take a small piece of ginger and place in a pot containing soil. • Cover it entirely with soil. • Water it every day.
20
Procedure: • Take a healthy onion bulb and place it in a pot containing soil. • Cover the onion bulb with soil. • Water it every day. • After a few days, you will observe new leaves growing. • Gradually, the bud will grow into a new plant. Observation: Onion plants grow with the help of onion bulbs through the method of vegetative propagation.
• Tubers: Tubers are stems that grow underground and are swollen, serving for food storage and reproduction. Tubers develop eyes which contain buds that are capable of growing into new plants. The food stored within the tubers is used up by the buds during the process of growing into a new plant. Potato is an example of a tuber. ACTION TIME
3
Aim: To observe vegetative reproduction in potato. Procedure: • Take a small part of the potato with an eye. • Place in soil (pot or ground). • Water it every day for a few days. • After some days, you will observe that new leaves are growing. Observation: The eye or the tubers of the potato grow into a new plant through vegetative propagation.
Reproduction by leaves
The leaves found in plants such as Bryophyllum are large and f leshy. At the margin of the leaves, several buds develop that grow roots and new leaves. These are capable of dropping off and forming new plants. The leaf of the plant may also break off from the parent plant and help the roots anchor into the soil, thereby leading to a new plant.
ACTION TIME
4
Aim: To observe vegetative reproduction in Bryophyllum. Procedure: • Take a leaf of Bryophyllum where the margin has small buds growing. • Place the leaf on soil in a pot. • Water it every day and after a few days you will observe each of the buds growing into a new plant. • The leaf may eventually wither off. Observation: The Bryophyllum plant grows with the help of leaves through vegetative propagation.
Fig. 2.13 Leaves in Bryophyllum can produce a whole plant Wither: Lose freshness
21
Reproduction by roots
form new plants. In Dahlia, the roots need to be planted along with the buds for them to grow into independent plants. The carrot plant has tuberous roots which also form buds just above its swollen tap root. In this case, this bud present at the base of the stem is used for reproduction.
Certain plants such as sweet potato, Asparagus, tapioca and Dahlia have f leshy and swollen roots. These are modif ied roots for the purpose of storage of food and are also known as tubers. Tubers are underground stems that are swollen since food is stored in them. These tubers grow roots and are capable of developing into Tissue Culture independent plants. The tubers of sweet potato Tissue culture involves the production or growth of grow adventitious roots that can be planted to plants in an artif icial or synthetic medium. Here, a kind of plant may be grown in a sterile medium in a test tube using small parts of an existing plant in a test tube. The medium used to grow plants in a test tube is rich in nutrients and suitable for the growth of the specif ic plant. Tissue culture ensures that a large quantity of healthy saplings are available that can be replanted in the soil where they grow as independent plants. Examples of plants that are cultivated using tissue culture are orchids and Asparagus. Fig. 2.14 Sweet potato reproduces by roots Tissue sample scraped from parent plant
Tissue samples placed in Agar growth medium containing nutrients and auxins
Samples develop into tiny plantlets
Plantlets planted into compost Fig. 2.15 The process of tissue culture
22
Auxin: A plant hormone that promotes root formation and bud growth | Agar: A gelling agent for culture medium
Asexual Reproduction in Animals This bud grows in size and develops parts of the
body. F inally there arises a constriction at the base of the bud from where it gets disconnected from the parent. This bud, that has now separated, is capable of living individually. Hydra reproduces by the method of budding. A bud is formed which grows in size and develops a mouth and tentacles around it. Later, this Budding daughter Hydra separates from the parent and In this method, there is formation of a bulge grows into an adult. or an outgrowth, known as bud, in the parent. Asexual reproduction is seen in very few animals and especially those of the lower group. Some examples of animals that reproduce asexually are Hydra, corals, liverworts, Amoeba and starf ish. The asexual methods of reproduction shown by animals are described as follows:
2
Hydra with a bulge known as bud.
Bud grows and forms a baby Hydra .
1
3
The bud is fully mature.
The fully mature baby Hydra separates from the parent. 4
Fig. 2.16 Hydra reproduces by budding
Binary Fission or Multiple Fission
During binary f ission, the nucleus present within the cytoplasm in the cell, divides into two (Fig. 2.17). The cytoplasm then develops a constriction in the space between the two nuclei and two separate cells are formed with one nucleus in each cell. This kind of reproduction is commonly seen in unicellular organisms such Constriction: Tight or narrow compression
as Amoeba, Paramecium and Euglena. When Amoeba becomes mature and is fully grown, the nucleus divides into two and two separate daughter cells are formed. Each of these cells is capable of living independently. They grow further, mature and again divide and thus, the process of binary f ission continues. 23
Parent cell
Nucleus Cytoplasm Two daughter dividing dividing cells Fig. 2.17 Binary fission in Amoeba
Multiple fission at the cellular level occurs in many protists. A method known as multiple f ission occurs in Amoeba to survive and reproduce under unfavourable conditions. When the conditions are unfavourable, Amoeba withdraws its pseudopodia and becomes almost round. It secretes a hard covering called cyst. Cytoplasm
Nucleus
Inside the cyst, the nucleus divides repeatedly to form many nuclei. This is followed by division of cytoplasm. This leads to the formation of many new daughter cells. When the favourable conditions return, the cyst bursts and releases these daughter cells.
Many daughter cells produced by multiple fission
Daughter cells released
Cell Cyst (protective wall) (a)
(b)
Cyst breaks (c)
Fig. 2.18 Multiple fission in Amoeba
Regeneration
Quick Check 1
Regrowing of a lost part of the body is def ined as A. Match the following: regeneration. Animals such as echinoderms Column A (example, starf ish), reptiles and amphibians have 1. Modified swollen roots 2. Strawberry the capacity of growing a lost part of their body. 3. Water hyacinth For example, a starf ish can regrow a lost arm. 4. Chrysanthemum 1 Thus, when an animal body breaks into two or2 5. Underground stem more pieces, each piece is capable ofArm regrowing to lost form complete animals. New arm growing
Arm lost New arm growing back
24
backB. Fill in the blanks.
2
1
Column B a. Runners b. Tubers c. Corm d. Spirogyra e. Offset f. Sucker
3 New arm fully grown
Fig. 2.19 Regeneration in a starfish 3 New arm fully grown
1. Asexual reproduction is also known as ........................ (vegetative/vegetation) reproduction.
2. Plants such as ferns, fungi and mosses reproduce by means of ........................ (spores/buds).
3. Budding is a method of vegetative ........................ (reproduction/ colouration) in plants.
4. ........................ (Hydra/Euglena) reproduces by the method of budding.
5. ........................ (Organ culture/Tissue culture) involves the production of plants in an artificial medium.
6. Hydra reproduces by method of ........................ (budding/tissue culture).
7. Regrowing of a lost part of the body is defined as ......................... (fission/ regeneration).
Sexual Reproduction in Plants Flowering plants display sexual mode of reproduction. In this method, there is an involvement of male and female organs or gametes. Sexual reproduction in plants takes place in the f lower. Let us understand the structure and various parts of a f lower. Floral Parts of a Flower
A typical f lower consists of the stalk, calyx, corolla, androecium and gynoecium. Each of these parts has a specif ic role to play. Some f lowers may or may not contain one or more of the parts, however the same function may be carried out by some other part of the plant.
Androecium
Gynoecium Stigma Anther
Stamen
Filament
Style
Corolla (Petal)
Pistil
Ovary Ovule Calyx (Sepal)
Thalamus
Pedicel
Fig. 2.20 Floral parts of a flower
Stalk
The stalk, also known as pedicel, is the connection between the f lower and the plant. It attaches the f lower to the stem. One end of the stalk is attached to the stem and the other tip is slightly f lattened and enlarged, where it bears the f lower. Thus, the point of contact of the stalk and the f lower 25
is known as the thalamus or the receptacle. The thalamus is attached to the four whorls of the f lower—calyx, corolla, androecium and gynoecium. Whorl is a circular arrangement of petals and sepals around a point or axis in a f lower. Androecium and gynoecium are the reproductive parts of the f lower. Calyx
This is the outermost whorl of the f lower. It is composed of several green leaf-like structures known as sepals. In some f lowers, the sepals may be differently coloured. The sepals cover and protect the inner parts of the f lower in the bud stage.
pollens dispersed in air. The style is a tube that leads from the stigma to the ovary and helps in passage of the pollen to the ovary. The ovary consists of ovules. INFO HUB Saffron, a flavouring agent that is used in various kinds of cooking, is harvested from the stigmas of a crocus plant called Crocus sativus.
Corolla
This is the second whorl of the f lower and is composed of coloured petals. The shape and size of the petals vary from species to species, and they make the f lower look attractive. In some f lowers, the petals may be absent. Androecium
Quick Check 2 Change one word in the following statements to make them correct. 1. Rhizomes can be stems or roots. 2. Ovules are also known as male gametes. 3. Sexual reproduction in plants takes place through the stem.
This is the male reproductive part of the f lower 4. The root, also known as pedicel, is the connection between the flower and the plant. and is made up of stamens. A stamen is made up of a long slender f ilament and a broad anther at the 5. Calyx is the second whorl of the flower and is made of coloured petals. tip. This anther contains several pollen grains that are in a form of a yellowish powdery substance. Pollen grains contain the male gametes. Pollination Gynoecium
This is the female reproductive part of the f lower and is the innermost whorl. It consists of pistils or carpels. Each pistil is made up of an enlarged ovary at the base, a long slender style and a broad stigma at the tip. The stigma is sticky in nature which is basically to attach the 26
The process of transfer of pollen grains from the stamens to the stigma of a pistil is known as pollination. Pollination may happen within the same f lower, within f lowers of the same plant or within f lowers of different plants. The process of pollination leads to fertilisation and eventually formation of seeds. Pollination is usually of two kinds—self-pollination and cross-pollination.
Self-pollination and Cross-pollination
Self-pollination: The transfer of the pollen grains from the stamens produced in one flower to the stigma of the same f lower or the stigma of another f lower blooming on the same plant is known as selfpollination.
Cross-pollination: The transfer of pollen grains from the stamens produced in one flower to the stigma of another flower of the same kind or species and which is blooming on a different plant is known as cross-pollination. Self-pollination
the stigma of another f lower. The pollen grains found on insect-pollinated f lowers are usually sticky or spiky so that they get attached easily. The stigma found in such f lowers is hairy which again aids in collecting pollens. Some examples of insect-pollinated f lowers are rose, Dahlia and sweet pea.
Cross-pollination
Stigma Stamen Fig. 2.22 Pollination by insects
Pollination by Wind Fig. 2.21 Pollination in flowers
Agents of pollination
There are several agents of pollination such as insects, wind and water. Pollination by Insects Several animals including squirrels and bats are responsible for pollination by carrying pollen. Birds and insects are among the most common carriers of pollens. The brightly coloured petals as well as the scent of the f lower attract insects and birds including butterf lies and bees. They reach the f lower in search of nectar and during the process of sucking nectar, the pollens get attached to their various body parts. The same insects or birds then reach another f lower which may be on the same plant or on another plant and that is when the pollen can fall and reach
Wind pollination takes place when the pollens that are ready for fertilisation, are blown away by wind and they fall on the stigma of another f lower. Flowers that are pollinated by wind need to produce pollens in large quantities, since there is no certainty that they will land at the right place. In fact, there are several pollen grains that do not land on the stigma. These f lowers need not be brightly coloured nor do they require to be scented or have presence of nectar, since they do not need to attract any organism. However, such f lowers have lengthy anthers that are extending out of the f lower, so that they are easily blown away by the wind. Wind-pollinated f lowers have feathery or light pollens, so that moving with the wind is easy. ies Also, the stigma is hairy which simplif collection of pollens from the air. Some examples of f lowers that are pollinated by wind include wheat, maize, conifers and grass. 27
Water Level
Male Flowers Pistillate Flowers
Pollen carried by wind
Staminate Flowers
Pollen caught on feathery stigmas Fig. 2.23 Pollination by wind
Anther is loaded with pollen. It dangles loosely from the filament, thus exposing the pollen
Fig. 2.25 Pollination in Vallisneria
Artif icial pollination
Artif icial pollination is usually carried out to Filament is long improve the variety of a particular plant. In and loose this method, the gynoecium is kept covered with paper or polybag, so that pollination does not take place naturally. Once the stigma of the f lower matures, carefully selected pollens from other f lowers are placed on these stigmas. The seeds produced in this manner possess characteristics of both plants and this new Stigma is feathery and ideally adapted variety is known as hybrid. Several varieties of to catch the pollen fruit-bearing plants such as mango and grains Fig. 2.24 Characteristics of a wind-pollinated flower such as rice, maize and wheat are produced Pollination by Water in this manner. The hybrid plant produced is of Plants that are pollinated by water are usually superior quality. aquatic. However, all aquatic plants are not necessarily pollinated by water. Some plants such as lotus have f lowers that bloom outside water and these are then pollinated by insects. Water-pollinated plants include Vallisneria and pond weeds. The pollens f loat in water and when they come in contact with the stigma of the female f lower, they get attached and undergo fertilisation. Fig. 2.26 Process of artificial pollination
28
Fertilisation
Quick Check 3
The process of fertilisation takes place when the male gamete from the stamens and the female gamete from the pistils of plants come in contact with each other. The pollens that are collected on the stigma grow a pollen tube that passes through the long tube known as style and reaches the ovary. The tip of the pollen tube then gets dissolved to release the male cells in the ovary where they fuse with the female ovule cells in the ovary to form the zygote. This fusion of male gametes and the female gametes is known as fertilisation. The ovule that contains the fertilised egg eventually develops into a seed. The ovary enlarges and converts into the fruit that bears the seeds. The covering of the ovule alters and changes into the seed coat. The parts of the f lower that are no longer required such as the petals and sepals eventually dry up and fall off. Pollen grain Stigma Style Polar nuclei Egg or ovule
Pollen tube Ovary Embryo sac
Fig. 2.27 Process of fertilisation in plants
INFO HUB The sunflower family including daisies and asters seems to have one large flower blooming. However, each flower is composed of hundreds of tiny flowers called florets, which ripen to become the seeds.
Fill in the blanks. 1. Pollination may happen within the .............................. flower. 2. The process of pollination leads to .............................. and eventually formation of seeds. 3. Transfer of pollen grains from the stamens produced in one flower to the stigma of the same flower is known as .............................. . 4. Transfer of pollen grains from the stamens produced in one flower to the stigma of the another flower is known as .............................. . 5. Birds and insects are among the most common carriers of .............................. . 6. .............................. takes place when the pollens that are ready for fertilisation are blown away by wind. 7. Water-pollinated plants include .............................. and pond weeds. 8. .............................. is usually carried out to improve the variety of a particular plant. 9. The fusion of male and female gametes is known as ............................. .
sexual Reproduction in HUMAN BEINGS Sexual reproduction involves the fusion of male and female gametes to form a fused zygote. The process of fusion is termed as fertilisation. As mentioned earlier, most of the animals reproduce by the method of sexual reproduction. The process of fertilisation is internal (that is, inside the female body). The fused zygote divides by the method of cell division whereby the cells multiply and grow, and they form an embryo. The embryo thus formed remains inside the female body and derives all the nutrition from there till it is mature enough to survive on its own. At the 29
appropriate time and when it reaches certain level of growth, the embryo is expelled from the body of the mother and is capable of surviving on its own. The young one that is born from the mother’s body eventually grows into an adult. Human Reproduction System
In humans, the reproductive system is different for males and females. Let us understand them one by one. Male reproductive system
The male reproductive system is primarily made up of a pair of testes (singular testis) that is located outside the abdominal cavity in a sac known as scrotum or scrotal sac. The male reproductive cells or male gametes are produced inside the testes. The male gametes are known as sperms. The testes consist of several sperm-producing Urinary bladder Ureter Seminal vesicle
Ductus deferens
Prostate gland
Bulb Epididymis Testis Penis Urethra a. Front view
Female reproductive system
Lobules Sperm-producing tubes Sperm
Fig. 2.28 Male gamete: Sperm
Bladder Pubic bone
Seminal vesicles
Vas deferens
Rectum
Urethra Anus
Penis Testicle
Fig. 2.29 Male reproductive system
The female reproductive system primarily consists of a pair of ovaries that bears the eggs or the female gametes known as the ova. The two ovaries are oval in shape and located in the lower part of the abdomen on either side of the uterus. The size of the ovary is about the same as that of an almond. A funnel-shaped tube known as the fallopian tube or the oviduct is present 30
tubes that join to form sperm ducts. The ducts from both the testes open up near the top of the urethra. Just before the opening of the ducts that is arising from each testis, there is a gland known as seminal vesicle. This gland, which is present in each testis, produces a substance that acts like the medium for the passage of the sperms. This liquid medium mixes with the sperms and forms the semen which is milky in nature. The sperms present in the semen reach the urethra which is present inside the penis. The semen is eventually released through the penis.
Scrotum b. Side view
close to the ovary. When the egg is released from the ovary, it passes through the fallopian tube to the uterus. But before it moves to uterus, it gets fertilised in fallopian tubes. The lower part of the uterus is narrow and is known as cervix. The opening of the cervix to the exterior is through a muscular tube called the vagina. The vagina is the part that receives the sperms from the male reproductive system.
Teaching Tip: New terms given in figures 2.29 and 2.30 can be briefly explained to students. Vas deferens: Tubes arising from each testis that transport sperms to urethra
Ovum
Sperms
Fig. 2.30 Female gamete: Ovum
INFO HUB The largest and the smallest cells are present in the human reproductive system. The smallest human cell is the sperm and the largest human cell is the egg.
Fallopian tubes
Implantation
Ovary Womb lining (endometrium)
Womb (Uterus)
Cervix Vagina
Fig. 2.31 Female reproductive system
ACTION TIME
head of the sperm that contains the nucleus penetrates the female egg and the tail is left behind. Thus, fertilisation takes place which is the process of fusion of the nucleus of the sperm with the nucleus of the egg.
5
The following are parts of the female and male reproductive systems. Against each part, note down its role in the process of reproduction. Vagina, Ovaries, Fallopian tubes, Seminal vesicle, Testes
Fertilisation During sexual intercourse, the semen from the male counterpart is received by the female vagina. There are millions of sperms present in the semen but only a few of them are able to travel to the upper part of the uterus. The sperms have a tail with the help of which they swim their way up towards the oviduct. The sperms that do not travel eventually die. The egg present in the oviduct gets fertilised by a single sperm. The
When the egg is fertilised by the sperm, it starts developing by repeated cell division and forms the zygote. Several cells form during the developing stage and this mass of cells f inally reaches the uterus. Here it gets f ixed in the wall of the uterus. This f ixing of the embryo in the uterus is known as implantation. At this stage, the female is said to be in a state of pregnancy. The growth process of the embryo takes place inside the uterus for the next few weeks where all the vital internal systems as well as the limbs develop. Quick Check 4 State whether the following statements are True (T) or False (F). Correct the false statements. 1. In human beings, the fertilisation is external. ...... 2. Testis is located in the fallopian tube. ...... 3. Female gamete is called the ovum. ...... 4. Implantation refers to the fixing of embryo in the uterus. ...... 5. Fertilisation involves fusion of two sperm cells. ......
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k e y T e rm s Reproduction: The process of living beings producing young ones of their own kind Asexual reproduction: A mode of reproduction in which the new offspring are produced from a single parent (by division or differentiation of the parent body) Vegetative propagation: A form of sexual reproduction in plants Sexual reproduction: The formation of new individual by the fusion of male and female gametes Whorl: A circular arrangement of petals and sepals around a point or axis in a flower Stalk: The connecting part between the flower and rest of the plant Calyx: The outermost whorl of the flower made up of sepals Corolla: The second whorl of the flower made up of petals Androecium: The male reproductive part of the flower composed of stamens Gynoecium: The female reproductive part of the flower composed of pistils or carpels Pollination: The process of transfer of pollen grains from the stamens to the style of a pistil Fertilisation: The fusion of male gametes and the female gametes producing a zygote Zygote: The fertilised egg
q u i c k not e s ✶✶ Living beings need to reproduce for the survival of species. ✶✶ Plants and animals reproduce by asexual as well as sexual methods. ✶✶ Plants such as ferns, fungi and mosses reproduce by means of spores. ✶✶ There are various ways of asexual reproduction in plants. The lower plants follow the method of
budding or fragmentation. The higher plants reproduce or multiply by using the parts such as roots, stems or leaves. ✶✶ Asexual methods include budding and binary fission which are seen in unicellular organisms like
Amoeba as well as in multicellular organisms like Hydra. ✶✶ In sexual reproduction, there is an involvement of male and female organs or gametes. ✶✶ A typical flower consists of the stalk, calyx, corolla, androecium and gynoecium. Each of these parts
has a specific role to play. ✶✶ Pollination is usually of two kinds—self-pollination and cross-pollination. ✶✶ There are several agents of pollination such as insects, wind and water. ✶✶ Fertilisation in plants leads to the formation of a zygote and then the seeds. ✶✶ In human beings, the male and female gametes called sperms and eggs are present in the male and
female species, respectively.
• In sexual method of reproduction, the fusion of the sperm and ovum results in the formation of a zygote which then forms a new individual.
• The fertilised egg is called a zygote which grows to become an embryo.
• The embryo gets fixed in the uterus and grows further.
• The young one is born when it develops to a certain size and is capable of independent survival.
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run-through I. Very Short Answer Questions. A. Fill in the blanks. 1. Sweet potato and tapioca have fleshy and ……………… (bulb/tuberous) roots. 2. Both runners and stolons are sub-aerial ……………… (roots/stems). 3. An example of ……………… (stolon/sucker) is Chrysanthemum plant. 4. ……………… (Corm/Root) is an underground stem that grows in clusters. 5. The ……………… (food/water) stored within the tubers is used up by the buds during the process of growing into a new plant. 6. The fusion of male cells and the female gametes is known as ………………. (reproduction/ fertilisation). 7. The carrot plant has ……………… (adventitious/tuberous) roots which form buds just above its swollen tap root. 8. Reptiles and ……………… (amphibians/birds) have the capacity of regrowing a lost part of their body. 9. There are ……………… (one/two) testis/testes in the human male reproductive system. 10. Seminal vesicle is a ……………… (gland/hormone) that is present in the testes. 11. Testes are located in ……………… (Scrotum/Penis).
B. Match the following: Column A 1. Spore formation 2. Fragmentation 3. Budding 4. Fallopian tube 5. Seminal vesicle 6. Insect-pollinated flowers 7. Water-pollinated flowers
Column B a. Hydra b. Fixing of embryo in uterus c. Fern d. Spirogyra e. Pollen produced in large quantities f. Oviduct g. Passage of sperms h. Brightly coloured i. Pollens are light and float on water
C. State whether the following statements are True or False. 1. Bulbs are fleshy, vertically growing short stems. 2. Rhizome is an underground stem that bears roots and shoots at the nodes. 3. Tubers are underground stems that develop eyes which contain buds that are capable of growing into new plants. 4. The leaves found in the Bryophyllum plant are large and fleshy.
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5. Tissue culture produces a large quantity of healthy saplings that can be replanted in the soil where they grow as independent plants. 6. The thalamus is attached to any two whorls of a flower. 7. When Amoeba becomes mature and is full grown, the nucleus divides into two, and two separate daughter cells are formed. 8. Regrowing of a lost part of the body is known as budding. 9. The male gametes are called eggs and the female gametes are called sperms. 10. Animals reproduce by sexual and asexual methods. 11. Budding is a sexual method of reproduction carried out by Hydra. 12. Amoeba is a unicellular organism that reproduces by the method of multiple fission. 13. Urethra in men serves as the passage for both urine and sperms.
D. Complete the concept map. Modes of reproduction
Asexual
Sexual
In plants
In animals Examples
Examples Hydra
Binary fission
Binary or Multiple fission
Starfish
Through stems, roots, leaves Examples • Stem: Potato • Root: Carrot • Leaf: Bryophyllum
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II. Short Answer Questions. A. Differentiate between: 1. Asexual and Sexual reproduction 2. Self-pollination and Cross-pollination 3. Stolon and Runner 4. Budding and Fragmentation 5. Binary fission and Multiple fission 6. Calyx and Corolla 7. Regeneration and Implantation
B. Answer the following questions. 1. What do you mean by binary fission? 2. Why do some plants bear long anthers? 3. How does vegetative reproduction happen in potato plant? 4. How does the carrot plant reproduce by means of vegetative propagation? 5. Explain multiple fission with the help of a diagram. 6. What do you mean by androecium? 7. What happens in sexual reproduction in plants and animals? 8. How does reproduction take place by leaves? 9. Describe the concept of artificial pollination. 10. What happens to the sperms that do not participate in the process of fertilisation? 11. List down the female reproductive parts. 12. What is another name for scrotum? What is its function?
C. Draw well-labelled diagrams of the following: 1. Male reproductive system 2. Female reproductive system 3. Self-pollination and Cross-pollination 4. Tissue culture
III. Long Answer Questions. 1. Describe the methods of asexual reproduction in plants. 2. Analyse the kinds of pollination based on their agents. 3. Explain how fertilisation takes place in a plant. 4. Explain with the help of a diagram the different parts of a flower. 5. What are the various methods of asexual reproduction in animals? 6. Describe the various parts of the female reproductive system. 7. Describe the various parts of the male reproductive system.
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IV. Challenge 1. How are tulips and daffodils able to reproduce by both sexual as well as asexual methods? 2. How are coconuts pollinated by water in spite of being large and heavy fruits? 3. Are plants, that do not have brightly-coloured petals, not pollinated by insects? 4. When twins are born, is only one egg fertilised which then divides to form two embryos, or are two eggs fertilised by two separate sperms? 5. Complete the flowchart and state what it depicts. Male child Adult .........................................
Produces male gamete ?
Adult female
Produces ................... ?
6. What does the following diagram depict? Label it.
V. Enrichment A. Know Your Scientists 1. Marcello Malpighi (1628–1694): An Italian physicist and biologist, Malpighi is widely known for his work in microscopic anatomy, physiology and embryology and is known as the founder of modern anatomy. arcello Malpighi was one of the first scientists to have used the newly invented M microscope to carry out his study on microscopic structures. He made important contributions in the field of physiology. Malpighi became widely acclaimed for his study of the life cycles of plants and animals which was significantly important in the topic of reproduction. He did a comprehensive study on the transformation of caterpillars into insects and also development of chick embryo.
Life Connect
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Embryo
2. Ramon Barba (b. 1939): A Filipino scientist, Barba is well-known for his scientific breakthroughs in the field of horticulture, that is, the science of growing and cultivating fruits, especially the advancements concerning the mango trees. amon Barba has played an important role in finding a solution to help the mango R export flourish in his country. His findings have had a positive impact on the yield of this fruit-bearing trees. He proposed a technique that he had developed to make mango trees flower more often which would lead to more fruit production. The technique involved use of smoke/gas that makes the plants flower three times a year instead of only once. Mango growers have benefitted immensely due to the research and findings of Ramon Barba.
B. PowerPoint Presentation: Nitya has started preparing a slide show on ‘Artificial Vegetative Propagation in Plants’. Help her complete the presentation. Subject Connect
(This can be done as a group activity.)
C. Model Making: Work in groups. Each group can make a model on any one of the following: 1. Male reproductive system
2. Female reproductive system
3. Binary fission in Amoeba
4. Fertilisation in plants
5. Parts of a flower
6. Budding in Hydra
Subject Connect
S c i e n t i f i c Q u e s t 1. Visit a garden near your house and find out about different variety of flowers that grow there. Now, try to observe or ask the gardener about how reproduction and pollination happen in the case of each flower. Note down your observation in a tabular format using the following heads: Name of the Flower, Reproduction Method, Mode of Pollination. Life Connect 2. Is vegetative reproduction good or bad? Explain by stating the advantages and disadvantages of it. Also, discuss in class.
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e n j oy s c i e n c e Reverse Crossword! Write the clues for the given crossword. 1.
c a l
2.
5.
c e
7.
f
r v
3.
t
a
g
m
z
e
y
s
g
t e s
4.
t e
y
b
r
x
i
d
e g
6.
o N
h
a
s t
e i
o
n
o
e
i
l
r
x
o
8.
a 9.
n
t
o u
b
e
i o n
P I C T UR E S UR V E Y 1. What does the picture depict? What happens in this process of reproduction? Tentacles
Bud
2. Identify the following pictures. Differentiate between them.
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c r
m
R A P I D F I R E 1 Fill in the blanks. 1. A ........................ is a group of cells that perform specialised function in organisms. 2. Modified roots for the purpose of storage of food are called ........................ . 3. Mutual attraction between water molecules is known as ........................ . 4. ........................ are the small openings in the cork of woody stems. 5. Spirogyra reproduces by the process of ........................ . 6. Maximum amount of ........................ in a plant body takes place through stomata. 7. ........................ are fleshy, vertically growing short stems. 8. The loss of water in liquid form from plant body is termed as ........................ . 9. I n ........................ reproduction, a single parent gives rise to the new individual. 10. Hydra reproduces by the process of ........................ . 11. I ncrease in wind speed, ........................ the rate of transpiration. 12. . ....................... is the term used to define the transport of food material from leaves to other parts. 13. Sexual reproduction in plants takes place in the ........................ . 14. Absence of ........................ causes yellowing of leaves with grey spots. 15. ........................ is an aquatic plant which is pollinated by insects. 16. In humans, the embryo gets fixed in ........................ .
Help box magnesium, flower, conducting, uterus, Lotus, decreases, increases, asexual, tissue, transpiration, cohesion, lenticels, guttation, budding, translocation, tubers, fragmentation, bulbs
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Ecosystems
Chapter
3
Chapter Objectives In this chapter, you will learn about: ♦♦ Ecosystem ♦♦ Biotic components ♦♦ Interdependence among organisms
♦♦ Abiotic components ♦♦ Forest ecosystem
‘All living things are natural, but all natural things cannot be living’. Discuss in class.
INTRODUCTION TO ECOSYSTEM All the living organisms in a particular area, interacting with each other, and also their non-living environments (weather, Earth, Sun, soil, climate, atmosphere, etc.) comprise the ecosystem. INFO HUB The term ‘ecosystem’ is derived from the Greek word ‘Oikos’, meaning ‘a house’.
In other words, our environment means our surroundings. Our environment consists of living things as well as non-living things. Living organisms such as plants and animals form the biotic components (living components) of an ecosystem. Non-living things such as soil, air, water and light are the abiotic components (non-living components) of our ecosystem.
Forests, ponds and grasslands are examples of The picture below shows the pond ecosystem. ecosystems. List from the picture, the: There exists a variety of things around us. The a. biotic components things around us constitute our environment. b. abiotic components
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Fig. 3.1 Pond ecosystem
Biotic Components
The biotic components of a forest are in the following sequence of food or trophic levels. Producers
consumers. Omnivores and scavengers are two other type of consumers. Omnivores such as human beings and peacock feed on both plants and f lesh of animals.
The green plants make their own food by the Some carnivores and omnivores, known as process of photosynthesis. Hence, they are called producers. They are also called autotrophs. scavengers, are animals that do not hunt other animals, but feed on the f lesh of dead animals. They They form the trophic level 1. are extremely important for the environment as Plants absorb and convert the solar energy they help to keep it clean by eating up the dead into chemical energy. This chemical energy bodies of various animals. Vulture, crow, jackal is transferred to other organisms as food. and hyena are well-known scavengers. Producers are the foundation of an ecosystem as they are the main source of energy and food to other organisms. Consumers
Animals and human beings cannot make their own food and obtain it from other Fig. 3.2 Hyenas feeding on flesh sources. Such organisms are called consumers or heterotrophs (heteros means ‘another’ and Decomposers trophe means ‘nourishing’). They are of three Decomposers are organisms that break down and types based on their feeding habits. feed on dead and decaying organisms. When a • The animals that feed on green plants are called plant or an animal dies, its decaying body is herbivores or primary consumers. The chemical broken down or decomposed by decomposers. energy of food from plants is directly passed The nutrients present in the dead body are returned on to them. Herbivores comprise the trophic to the soil by the action of decomposers. Bacteria and fungi are the most important decomposers. level 2.
• The herbivores are then eaten by carnivores or secondary consumers. The chemical energy of food from plants is indirectly passed on to them through herbivores. Carnivores comprise the trophic level 3.
• The carnivores are then eaten by tertiary consumers. They are animals that feed on the f lesh of other organisms (primary and secondary consumers). The chemical energy is passed on to them through primary or secondary
Fig. 3.3 M ushroom (a fungi) growing on a broken twig
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Quick Check 1 State whether the following statements are True or False. 1. Autotrophs belong to the trophic level 1.
..............................
2. Plants are also referred to as heterotrophs.
..............................
3. Scavengers are tertiary consumers.
..............................
4. Bacteria are scavengers.
..............................
5. Vulture and crow are examples of herbivores.
..............................
FOOD CHAIN In nature, some animals eat plants whereas some eat other animals. The feeding habits of animals link them with each other. Consider the following link between plants and various animals.
Plants
Grasshopper
Frog
Eagle
Snake
Fig. 3.4 A simple food chain
Note that the link follows a sequence. A grasshopper feeds on green plants. It is eaten by a frog. The frog becomes the food for a snake, and f inally the snake is eaten by an eagle. The food chain gives us an idea about the transfer of food energies from the herbivorous to the carnivorous animals. A food chain is a sequence which shows how living things in an environment are related to each other according to their feeding habits. All food chains begin with plants, as plants make their own food by photosynthesis. Animals eat either plants or other animals. The arrows in a food chain show its direction. All animals depend upon plants either directly or indirectly. Thus, a simple food chain can also be given as: Producer (Plants)
Primary Secondary Tertiary Consumer Consumer Consumer (Snail) (Frog) (Kingfisher)
Let us consider another example of a food chain (Fig. 3.5). Here, the grass is eaten by the grasshopper. The grasshopper is eaten by a rat. The rat is eaten by a snake. The snake gets eaten by an eagle or vulture. An eagle or vulture when dies is decomposed by the decomposers, such as mushrooms. What do you think will happen if there are no green plants?
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Vulture
Snake Rat
Grasshopper
Grass Mushroom Fig. 3.5 A food chain
Quick Check 2 Build the food chains by numbering the living things correctly.
1 a) Mouse
Plants
2
Owl
3
4
Caterpillar
b) Lion Goat Grass Jackal
Food Web
Food web is basically several interlocking and independent food chains in an ecosystem. Each living organism in the ecosystem is a part of multiple (different food) chains. For instance, a grasshopper and giraffe are herbivores. Similarly, different herbivores can be eaten by different carnivores. Thus, we see that there are a lot of food chains that prevail in an ecosystem which are interconnecting, overlapping and interdependent in nature. Hence, we can describe food web as a network of food chains that are linked together in one form or the other. Producers (green plants making nutrients with photosynthesis)
solar energy
red-tailed hawk
Scavengers (vulture)
Secondary Consumers (carnivores) squirrel
fox
Primary Consumers (herbivores)
Producers (green plants)
(fungi) rabbit
mouse decomposers (fungi and bacteria) detritus feeders (insects and worms) Fig. 3.6 A forest food web
Detritus: The remains of something that has been destroyed or broken up
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PYRAMID OF NUMBERS The pyramid of numbers is a graphical representation that depicts the relationship in terms of the number of producers, herbivores and the carnivores at their successive trophic levels. You will observe that there is a decrease in the number of individuals from the lower to the higher trophic levels. Different ecosystems have different pyramids of number. The three types of pyramid of numbers are: • Upright pyramid of number
• Partly upright pyramid of number • Inverted pyramid of number
Carnivores Woodpecker (Secondary consumer)
Herbivores
Insect (Primary consumer)
Producers
Oak tree (Producer)
Partly Upright Pyramid of Number
Fig. 3.8 Partly upright pyramid of number
Inverted Pyramid of Number
Upright Pyramid of Number
This type of ecological pyramid is seen in Aquatic and grassland ecosystems have this type parasitic food chain where one primary producer of pyramid of number. The pyramid is upright supports numerous parasites which support because these ecosystems have numerous more hyperparasites. small autotrophs which in turn support lesser herbivores. The herbivores support a still smaller number of carnivores.
Tertiary consumer (Lion) Secondary consumer (Fox) Primary consumer (Deer) Producers (Grass) Pyramid of Number
Upright pyramid
Hyperparasites
Fig. 3.7 Upright pyramid of number
Parasites
Herbivores
Producers
Partly Upright Pyramid of Number
This type of pyramid of number is seen in the forest ecosystem. Here, the number of producers are lesser in number and support a greater number of herbivores. These herbivores in turn support a fewer number of carnivores. 44
Ecology: The environment as it relates to living organisms
Inverted pyramid of number Fig. 3.9 Inverted pyramid of number
INFO HUB
But how do you think plants benefit from animals?
Organisms that live on or inside the bodies of other living organisms are called parasites. For example, tapeworms are parasites that live inside the bodies of some animals and feed on the food digested by these animals. The organism that provides food and shelter to a parasite is called host.
The different organisms in the forest along with plants and animals are all interdependent. They depend on each other for food, protection and shelter. Hence, it is important to control this biodiversity by managing the balance between the two.
Energy is transferred along food chains from one trophic level to the next. However, the amount of available energy decreases from one trophic level to the next.
Some of the ways of interdependence are predation, parasitism and symbiosis.
Energy f low in an ecosystem starts from the Sun which produces all the energy needed for life. Then comes the producers, the autotrophs. These organisms harness the energy of the Sun and convert it into sugars. These organisms obtain 100 % of the energy they produce. The primary consumers which eat the autotrophs get the next most energy, but this is only 10 % of the original energy that the autotrophs get. Next, the secondary consumers, which eat the primary consumers get nutrients, but this is only 1% of the energy that was originally in the plant. Tertiary consumers, at the top of the food chain eat secondary and primary consumers, and they only get 0.1% of the energy.
Predation: In an ecosystem, predation is a biological interaction where a predator (an organism that is hunting) feeds on its prey (the organism that is attacked). For example, in the food chain (F ig. 3.4), frog is the predator for grasshopper, the prey. While, frog is the prey for the snake, the predator. Parasitism: It is a non-mutual relationship between species, where one species, the parasite, benef its at the expense of the other, the host, sometimes without killing the host organism. Fleas or ticks that live on dogs and cats are parasites. They live on the blood of the host animal.
INFO HUB At every level of the energy pyramid, the organisms only get 10% of the energy from the previous level.
Definitive host
Flea eggs
Flea larva
INTERDEPENDENCE BETWEEN ORGANISMS We know that plants are very useful to humans and animals. Definitive host: An organism that supports a parasite
Flea pupa Flea adult Fig. 3.10 An example of parasitism
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Symbiosis: It is an interaction between two Dependence of Plants on Animals different organisms living in close physical • Carbon dioxide: Animals take in oxygen and association, typically to the advantage of both. release carbon dioxide while breathing. This Symbiosis is a mutually benef icial relationship. carbon dioxide in turn is utilised by the plants For example, a group of soil bacteria called in the process of photosynthesis and oxygen is Rhizobia live in the root nodules of leguminous released. crops. In turn, these bacteria f ix atmospheric • Pollination: Animals help plants to reproduce nitrogen turning it into usable form of nitrogen through pollination. Animals such as insects, for the plants. birds and other animals help the plants by carrying the pollen grains to various places for pollination.
Root nodules
Fig. 3.11 An example of symbiotic relationship
• Seed dispersal: The animals help the plants with the process of seed dispersal. The fruits are eaten by animals and birds. They then walk or f ly to distant places and spread the seeds which come out with their droppings. Some seeds stick to the furs of the animals or birds and are carried from one place to the other.
ABIOTIC COMPONENTS OF THE ENVIRONMENT
‘Abiotic’ components mean ‘non-living’ components. Sunlight, air, water, soil and • Food: All animals, directly or indirectly, temperature are some of the abiotic components depend on plants for their food. For example, of the environment. These components form an herbivores eat plants, and carnivores and important part of the organism’s habitat. omnivores feed on herbivores. Dependence of Animals on Plants
• Oxygen: The plants take in carbon dioxide for photosynthesis and give out oxygen in the atmosphere. Animals take in this oxygen while breathing.
• Shelter: Some animals such as monkeys and birds depend on plants for shelter. Some animals make holes in the trees and live there. Birds build their nests on the trees. There are a number of insects such as grasshopper, moths and ants that live on the trees. 46
Sunlight
Sunlight is essential for all living organisms on the Earth. Green plants photosynthesise in the presence of sunlight. All animals depend on plants for food, either directly or indirectly. Plant-eating animals feed on plants. Flesheating animals, in turn, eat plant-eating animals. So, sunlight is the ultimate source of energy for all living organisms. Length of a day also inf luences the reproductive cycle of poultry and birds.
Poultry: Domestic fowls, including chickens, ducks, geese, etc.
water that nutrients and waste materials move throughout the body. Water is one of the important factors for seed germination. Water is the habitat for many organisms such as lotus, water lily, f ish, whale, shark and seahorse. Some organisms need oxygen dissolved in water to survive. Fig. 3.12 Plants make their food in the presence of sunlight
Air
Air is a mixture of several gases. Oxygen and carbon dioxide are two main gases that support life on the Earth. Plants need carbon dioxide for preparing their food by photosynthesis. Both plants and animals use oxygen for respiration. Carbon dioxide is exhaled by animals. It is also added to the environment by burning of fuels. Oxygen is given out by plants during photosynthesis. What is the percentage of following gases in the atmosphere—Oxygen and Carbon dioxide?
Fig. 3.13 Deer drinking water
Humidity is a quantity representing the amount of water vapour in the atmosphere or in a gas. Humidity also affects the type of organisms in an area. Soil
Soil is the top layer of the Earth’s surface in which Moving air is called wind. Wind is one of the plants grow. It is a mixture of f ine rock particles, agents of dispersal of seeds. Air also helps birds minerals, microorganisms and decomposed bodies of plants and animals. Soil also contains to f ly. water. Name one seed dispersed by wind. ………...............……………………….
Soil provides the medium for plant growth. It is the habitat for many animals such as snails, Water earthworms and ants. Soil can be of various The human body is about 60 % water by weight. types—clay, sand, silt and loam. Our body cells, tissues, blood and even bones contain water. Like human beings, bodies of all Temperature living organisms contain water. Plants absorb Temperature is a measure of warmth or coldness water from the soil through their roots. Water of a substance or environment. Sun’s heat reaches is a raw material essential for photosynthesis. the Earth and makes it warm. Being just at the Water acts as a medium of transport in the right distance from the sun, our planet Earth bodies of both plants and animals. It is through has a temperature that favours the growth and Teaching Tip: It can be explained to students that fat tissue does not have as much water as lean tissue. In adult women, fat makes up more of the body than men, so they have about 55% of their bodies made of water.
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survival of living organisms. Moreover, the layer of air around it helps to retain the heat and not let it escape. Without air, the Earth would be too cold to live! On the Earth, places near the poles are very cold while those near the middle part are hotter. That is why, very few organisms live in polar regions. Temperature affects the distribution of plants and animals on the Earth.
Forest Ecosystem Forests cover one-third of the Earth’s land. The land area covered mostly by trees and plants form a forest. A vast variety of plants and animals are seen in a forest. Depending on the kind of vegetation, forests can be classif ied into tropical rainforest, temperate and boreal forests. Tropical Rainforest
The climate in a tropical rainforest is hot and it receives heavy rainfall. The heavy rainfall causes f looding, soil erosion and rapid leaching of nutrients from the soil. INFO HUB Tropical rainforests are found along the equator, between Tropic of Cancer and Tropic of Capricorn. Subject Connect
Fig. 3.14 The Earth has a temperature that favours life
Animals whose body temperature changes with the outside temperature are called cold-blooded animals. For example, insects, most reptiles and amphibians. Animals whose body temperature does not change with the outside temperature are called warm-blooded animals. For example, birds and most mammals.
The loss of water soluble plant nutrients from the soil, due to rain and irrigation, is referred to as leaching. Plants grow rapidly and quickly use up any organic material left from decomposing plants and animals. As a result, soil is nutrient-def icient.
Flora: The tropical rainforest is very thick, and Thus, we now know that the biotic components not much sunlight is able to penetrate the forest are closely dependent on abiotic components.* f loor. However, the plants at the top of the Quick Check 3 Fill in the blanks. 1. Plants are …………………………. (tertiary consumers/producers). 2. Aquatic ecosystems have ……………………….. (upright/partly upright) pyramid of number. 3. ……………………… (Predation/Symbiosis) is a mutually beneficial relationship. 4. Animals help the plants with the process of ……………………… (seed dispersal/photosynthesis). 5. The amount of water vapour in the atmosphere is called ………………………….. (humidity/soil). 6. The measure of warmth or coldness of a substance is called …………………(sunlight/temperature).
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Leaching: The process of percolating *Note: Quick Check 3 is before the topic ‘Forest ecosystem’.
rainforest get about 12 hours of intense sunlight Temperate Forests every day throughout the year. Temperate forests correspond to forest In a rainforest, many trees such as mangroves concentration formed in the northern and southern hemispheres or in temperate regions. have special supporting roots like stilt roots. Due to the thick canopy of large trees, small The main characteristics include: wide leaves, large and tall trees, large wild canopy and nonplants climb on others to reach the sunlight. seasonal vegetation. The temperate deciduous Many creepers and climbers grow in a rainforest. forest has four seasons—winter, spring, summer The plants in a rainforest have a smooth bark and autumn. Animals and plants have special and leaves. Rain falling on the forests drips adaptations to cope with these yearly changes. down from the leaves and trickles down the tree Adaptation means the ways in which plants and trunks to the ground. The plants have shallow animals change to suit the conditions in which roots to help capture nutrients from the top they live. level of the soil. Flora: The word ‘deciduous’ means that the A rainforest has many epiphytes such as leaves on these trees change colour in autumn, epiphytic orchids. Epiphytes are plants that live fall off in winter and grow back again in on other plants and instead of collecting water spring. In winters, these forests get snow with roots, they obtain water and minerals and hail so deciduous plants lose their from rain and from debris that collects on the leaves to conserve water. Deciduous trees supporting plants through hair on their leaves. have broad leaves to capture energy from the Fauna: Rainforests are tremendously rich in Sun and convert it to food by photosynthesis. animal life. Rainforests are populated with Some of the food is used for growth and insects like butterf lies; arachnids like spiders; some is stored. They store food in the roots reptiles like snakes; amphibians like frogs; birds for the winter when the tree has no leaves like parrots and mammals like sloths. and cannot make any food. Some deciduous trees are black walnut, red maple, poplar, birch and willow.
a. Mangrove trees
Fauna: Animals living in these forests adjust to cold winters by hibernating or migrating. During winter, leaves fall off trees, leaving animals with less covers to hide themselves from predators. Some of the animals found here are the black bear, raccoon, wild boar, turkey and rat snake.
b. Sloth Fig. 3.15 Flora and fauna of tropical rainforests Trickle: Run or flow • Debris: The remains of something that has been destroyed or broken up
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droop downward to help shed excess snow and to keep the branches from breaking. Fauna: Some animals that live in the coniferous forest are hawks, owls, lynxes, snowshoe rabbits and wolverine. Most of the animals migrate on the onset of winters. a. Red maple
b. Rat snake Fig. 3.16 Flora and fauna of temperate forests
a. Fir tree
Boreal forests
Boreal also known as taiga forest or snow forest is characterised by coniferous forests consisting mostly of pines, spruces and larches. Most of these trees are evergreen. The taiga has cold winters and warm summers. Some parts of the conifers have a permanently frozen sublayer of soil called permafrost. Drainage is poor due to the permafrost or due to layers of rocks just below the soil surface. The soil is acidic and mineral-poor. It is covered by a deep layer of partially decomposed conifer needles. Flora: Most trees in a taiga forest have trees with needle-like leaves which prevent water loss in freezing weather and shed snow more easily than broad leaves. Waxy coating on needles prevents evaporation. The leaves are dark in colour allowing more solar heat to be absorbed. Coniferous trees (pine, f ir and spruce) have branches that
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b. Lynx Fig. 3.17 Flora and fauna of boreal forests
Quick Check 4 State whether the following statements are True (T) or False (F). 1. Tropical rainforests receive heavy rainfall. …. 2. Forests cover one-third of the Earth’s surface. …. 3. Deciduous trees have narrow leaves.
….
4. Boreal forest is known as snow forest.
….
5. The drainage in boreal forests is very well maintained.
….
k e y T e rm s Ecosystem: The interaction of all the living organisms in a given area, along with the non-living components in their environment Biotic components: All the living components in an ecosystem Abiotic components: All the non-living components in an ecosystem Producers: Organisms that produce their own food. Also referred to as autotrophs. Consumers: Organisms that cannot prepare their own food and obtain it from other sources. Also referred to as heterotrophs. Herbivores: They are plant-eating animals. They are also called primary consumers. Carnivores: They are flesh-eating animals. They are also called secondary consumers. Omnivores: Animals that feed on both plants and flesh of other animals Scavengers: Some carnivores and omnivores that feed on the flesh of dead animals Decomposers: Organisms that break down and feed on dead and decaying organisms Food chain: A series of organisms, each dependant on the next as a source of food Food web: Several interlocking and independent food chains in an ecosystem Pyramid of numbers: A graphical representation that depicts the relationship among organisms in terms of the number of producers, herbivores and carnivores at their successive trophic levels Predation: A biological interaction where a predator feeds on its prey Parasitism: A non-mutual relationship between species, where one species, the parasite, benefits at the expense of the other, the host Symbiosis: A mutually beneficial interaction between two organisms
q u i c k not e s ✶✶ Our environment consists of both biotic and abiotic components. ✶✶ The biotic components of forests are in the following sequence of food or trophic levels—producers,
consumers and decomposers. ✶✶ All animals depend on plants directly or indirectly. ✶✶ The three types of pyramid of numbers are—upright pyramid of number, partly upright pyramid of
number and inverted pyramid of number. ✶✶ Energy is transferred along food chains from one trophic level to another. However, the amount of
available energy decreases from one trophic level to the next. ✶✶ At every level of an energy pyramid, the organisms get 10% of the energy from the previous level. ✶✶ Plants and animals are interdependent. Some ways are—predation, parasitism and symbiosis. ✶✶ The abiotic components of the environment are—sunlight, air, water, soil and temperature. ✶✶ Forests can be classified into—tropical rainforest, temperate forest and boreal forest.
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run-through I. Very Short Answer Questions. A. Tick (✓) the correct option. 1. Which of the following is not an abiotic component? a. Soil
b. Light
c. Plant
d. Air
c. Cow
d. Humans
2. Which of the following is a scavenger? a. Crow
b. Peacock
3. Which of the following (in a food chain) will be the tertiary consumer? a. Frog
b. Snail
c. Grass
d. Both b and c
4. Partly upright pyramid of number is seen in ......................... ecosystem. a. Grassland
b. Aquatic
c. Forest
d. None of these
c. plant
d. host
5. Flea is an example of a ......................... . a. parasite
b. prey
6. ......................... acts as a medium of transport in the bodies of both plants and animals. a. Juice
b. Coffee
c. Tea
d. Water
7. Animals whose body changes with the outside temperature are called ......................... -blooded animals. a. warm
b. cold
c. hot
d. ice
c. stilt
d. pointed
8. Mangroves have ......................... roots. a. prop
b. tendril
B. Name the following: 1. A biotic component: .................................... 2. Organisms that cannot make their own food and obtain it from other sources: ............................... 3. Carnivores are also referred to as: .................................... 4. A decomposer: .................................... 5. Many interlinked and independent food chains: .................................... 6. A parasite: .................................... 7. Bacteria in symbiotic relationship: .................................... 8. A cold-blooded animal: .................................... 9. A warm-blooded animal: .................................... 10. A flora of tropical rainforest: .................................... 11. A fauna of boreal forest: .................................... 12. A flora and fauna of temperate forest: ....................................
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C. State whether the following statements are True or False. 1. Producers are the foundation stone of an ecosystem. 2. Autotrophs cannot make their own food. 3. Omnivores feed on the flesh of dead animals. 4. Scavengers help in keeping the environment clean. 5. Fungi is an example of a decomposer. 6. Plants and animals are not dependent on each other. 7. Leguminous plants and Rhizobia have symbiotic association. 8. Parasites live on the blood of the host animal. 9. Air is a mixture of several gases. 10. Sunlight is essential for photosynthesis.
D. Complete the concept map. Abiotic Components of the Environment
Role
Role
Role
Role
Role
Now, make a concept map on the following: 1. Forest ecosystem
2. Interdependence among organisms
3. Pyramid of numbers
4. Biotic components in a forest ecosystem
II. Short Answer Questions. A. Give reasons. 1. Both abiotic and biotic components are essential for an ecosystem. 2. Producers are the main source of energy. 3. Scavengers help to keep the environment clean.
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4. Organisms are interdependent. 5. Energy is transferred among food chains. 6. Animals are helpful to plants. 7. Parasitism is a non-mutual relationship. 8. Air is a mixture of several gases. 9. Not much sunlight is available to penetrate the forest floor in tropical rainforests. 10. Most trees have needle-like leaves in taiga forests.
B. Distinguish between: a. Biotic and Abiotic components
b. Autotrophs and Heterotrophs
c. Decomposers and Scavengers
d. Food chain and Food web
e. Parasitism and Symbiosis
f. Cold- and Warm-blooded animals
C. Answer the following questions. 1. How are plants dependent on animals? 2. How are animals dependent on plants? 3. Why does the available energy decrease from one trophic level to the next? 4. Explain the biotic components of a forest in the correct order of trophic sequence. 5. Explain food chain, giving suitable example(s). 6. Explain food web, giving suitable example(s).
III. Long Answer Questions. 1. Explain the pyramid of numbers and its types. 2. Explain some ways of interdependence among organisms. 3. List and explain the abiotic components of an ecosystem. 4. Explain the flora and fauna in the forest ecosystem.
IV. Challenge 1. The abiotic conditions in different forest ecosystems are different. Why? 2. What will happen if any one of the trophic level is not there in a food chain?
V. Enrichment A. PowerPoint Presentation: The class can be divided into groups. Each group has to select one topic amongst the following. A topic cannot be repeated. Search the Internet, school library, newspapers, etc. Prepare a PowerPoint presentation and present it in class. Subject Connect Life Connect
1. Evergreen vs Deciduous trees 2. The global environmental movements 3. Structural and behavioural adaptations 4. The Nature Writers
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B. Know Your Scientist—Joel Asaph Allen
Joel Asaph Allen was an American zoologist, mammalogist and ornithologist.
Life Connect
He is known for Allen’s rule, which states that the bodies of endotherms (warm-blooded animals) vary in shape with climate, having increased surface area in hot climates to lose heat and minimised surface area in cold climates to conserve heat. He became the first president of the American Ornithologists’ Union, the first custodian of a collection of birds and mammals at the American Museum of Natural History, and the first head of that museum’s Department of Ornithology.
C. Report Writing and Role play: Make a report on ‘Extinction is forever—How can we help?’. The report can be submitted to the subject teacher. Then, a role play can be held in the school assembly to spread awareness about the same.
D. Information Gathering: The Amazon is the world’s largest and most famous rainforests. Find out: • Where are they located? • What are the flora and fauna? • How much area does it cover?
Life Connect
• How is human activity affecting these forests? Make a two-page write-up on this in your notebook.
E. Field Visit: Visit the nearby park or garden. List down all the animals that you see. Make food chain(s) using those organisms.
S c i e n t i f i c Q u e s t Lichens are organisms that are made up of two living organisms. Both benefit from one another. Questions to ponder: • What kind of organisms are lichens made up of? • What kind of shapes do they have? • What kind of plants do lichens seem to grow on most often? • Can different kinds of lichens grow on the same tree? • How do they eat food?, etc. Make a PowerPoint presentation and present in class.
British soldier lichen
Green map lichen
Custodian: One having charge of buildings, grounds or animals
Oakmoss lichen
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e n j oy s c i e n c e Reverse Crossword! Write the clues for the following crossword. Give one example of each. 1
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P I C T UR E S UR V E Y A. The seeds shown in the picture given below are dispersed by animals. Identify the seeds and the animal.
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f
i
c
e
s
B. The picture here shows a variety of animals. Construct at least five food chains using them. Also, construct three food webs. Also, calculate the energy that will be passed on from one trophic level to another.
omnivorous
carnivores
decomposers
herbivores
bacteria
fungi
producers
trees bushes grass
worms
C. Look at the picture given below carefully.
1. Identify the plant. 2. To which forest ecosystem does it belong? 3. What type of leaves does it have and why?
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R A P I D F I R E 2 State whether the following statements are True or False. 1. A food chain links living things in an environment according to their feeding habits. 2. Heterotrophs feed on plants and animals both. 3. Any living organism can be a part of multiple food chains. 4. The amount of energy available remains the same from one tropical level to other. 5. Predation is a biological interaction where a parasite eats its prey in an ecosystem. 6. Even carnivores depend on plants for their food. 7. All living organisms depend on sunlight for food. 8. Humidity is defined as the amount of water vapour at a place. 9. Wind helps in pollination as well as transportation. 10. Animals have fixed body temperature and it does not change with the outside temperature. 11. Leaching takes place in tropical rainforest. 12. Deciduous means the leaves change colour every winter. 13. All plants and animals are interdependent in various ways. 14. Human body is 60% water by volume. 15. Food web contains several interlocking and independent food chains in an ecosystem.
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Practice Test Paper 1 I. Fill in the blanks. 1. Grasshopper and giraffe are ………………., and can be eaten by different carnivores. 2. ………………. is the multilayered waxy deposit that generally covers the leaves of the plants. 3. An underground stem that grows in clusters and is round in shape is ………………. . 4. ………………. is the connection between the flower and the plant. 5. ………………. carries water and minerals from the soil to leaves of a plant.
II. State whether the following statements are True or False. 1. Plants can’t absorb water through their entire surface. 2. In sexual reproduction, both male and female parents are involved. 3. Phloem carries food from leaves to various parts of the plant. 4. The word ecosystem means house. 5. Insects, wind and water are agents of pollination. 6. Animals living in forests cannot adjust to cold winters. 7. Roots are covered by multilayered layer called epidermis. 8. Energy decreases during transfer in food chains. 9. The tail helps the sperms to swim their way up towards the oviduct. 10. Oxygen and carbon dioxide support life on the Earth.
III. Unscramble the words to find the answer. 1. Measure of warmth or coldness of a substance or environment. (ETETEMPARRU) 2. Attraction of water molecules to a surface. (HADSEOIN) 3. Fusion of male and female gametes. (REFTIILASIONT) 4. Taiga or snow forests. (RBOELA) 5. The cells that assist the sieve tubes to function. (OPCMAINNO)
IV. Answer the following questions. 1. What are the differences between sexual and asexual reproduction? 2. How do plants carry water? 3. How does soil affect plant growth? 4. State different ways in which plant loses water. 5. Briefly explain the uses of stomata to a plant.
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Chapter
4
Human Body
Chapter Objectives In this chapter, we will learn about: ♦♦ Nervous system ♦♦ Endocrine system ♦♦ Adolescence
♦♦ Circulatory system ♦♦ Lymphatic system
Neerav is 12-year old. His mother says, ‘Neerav, your heavy voice is a part of growing up’. What does she mean by this?
INTRODUCTION The various processes of the human body include respiration, digestion, excretion, growth, circulation, etc. These processes are being carried out by specialised organs that are interrelated and interdependent. There is usually coordination between these organ systems because of which they can function smoothly. Coordination is def ined as the interaction and interrelation between the various activities in the body of a living being that takes place internally and externally. Coordination can be of two types—nervous coordination and chemical coordination.
THE NERVOUS SYSTEM The coordination of the nerves and the brain is part of the nervous coordination. This is highly specialised and involves reactions from simple to complex actions and also to internal and external stimuli. The actions of the body could be voluntary or ref lex. Voluntary actions are those that are under our control or we are conscious of such 60
actions. Ref lex or involuntary actions are those that are in response to external or internal stimuli. Structural and Functional Unit: The Neuron
Neurons or nerve cells are the smallest structural and functional units of the nervous system. Each neuron consists of a main cell as the body which is known as a cyton, and a number of processes or f inger-like extensions known as dendrites that arise from the cell body (F ig. 4.1). Each process could be long wire-like and is known as axon or nerve f ibre. The cyton or cell body consists of a nucleus. When messages are transmitted from the organs, they are received by the dendrites and passed on to the cell body and the axon. The axon is covered by a protective fatty covering called the myelin sheath. The axon then transmits the message either to the glands, which then secrete the hormones, or to the muscles which then contract to deliver the necessary response. The neurons can make contact by being in proximity with their processes.
The axon of one neuron lies close to the dendrites of another neuron. Each branch of a neuron ends into a bulb-like structure, called synapse or synaptic bulb. This bulb contains neurochemicals or neurotransmitters. The messages are transmitted from the axon of one neuron to the dendrite of another neuron via the synapse. Nucleus Vesicles
Reuptake pump Neurotransmitter Receptor
Synaptic cleft
INFO HUB Axon
The synaptic cleft separates the axon terminal from the dendrites of the next cell.
Myelin sheath Dendrites
Fig. 4.1 Nerve cells
A bundle of axons or nerve f ibres which are enclosed in an elongated sheath or casing form the nerve. The sheath or casing over the axon carries out the function of insulation, since it prevents the mixing of impulses that may be transmitted in adjacent f ibres. Nerves are of three kinds as discussed here. 1. Sensory nerves: These contain sensory f ibres that carry impulses from the sense organs to the brain or the spinal cord. 2. Motor nerves: These contain motor f ibres that carry impulses from the muscles or glands from the brain to the spinal cord.
3. Mixed nerves: These contain both sensory as well as motor f ibres.
The human nervous system is the centre of communication and control in the human body. It comprises the following three parts: the central nervous system (CNS), the peripheral nervous system (PNS) and the autonomic nervous system (ANS). Central Nervous System
The central nervous system consists of the brain and the spinal cord. The brain is enclosed within the skull and the spinal cord lies within the vertebral column. The major decisions and control functions are carried out by the brain and hence, it becomes the most critical part of the body organ system. The brain is made up of three main parts: cerebrum, cerebellum and medulla oblongata. 61
Cerebrum
Cerebellum
Medulla oblongata Fig. 4.2 The human brain
The cerebrum is the largest and most complex part of the brain. The cerebrum is the main control centre and is the seat of intelligence, willpower and consciousness. It controls the various voluntary activities and functions such as memory, thought, language, speech and perception. The cerebellum is positioned behind and below the cerebrum. It is much smaller in size. It is responsible for maintaining a balance in the body and in coordinating muscles and their activities. Medulla oblongata or brain stem is the lowest part and continues till the spinal cord. It controls the activities of the internal organs such as beating of the heart and breathing. These are also known as involuntary actions. The spinal cord begins at the medulla oblongata of the brain and extends inside the vertebral column or backbone almost till the end. The main function of the spinal cord is to assist in transfer of information between the brain and the various parts of the body and control ref lexes below the neck. It is the focus for ref lex actions. 62
Fig. 4.3 Spinal cord
Peripheral Nervous System
Peripheral nervous system consists of nerves that arise from the brain and the spinal cord. Depending on where they arise, the nerves that arise from the brain are known as cranial nerves and those that arise from the spinal cord are known as spinal nerves. The peripheral nervous system consists of 12 pairs of cranial nerves and 31 pairs of spinal nerves. These nerves connect the central nervous system to all other parts of the body. The impulses that are carried through the nerves can be passed only in one direction. Some Important Terms Related to Nervous System
There are some important terms related to the functioning of nervous system: Stimulus: This means the change that happens outside the body in the environment and which in turn causes a change in the body. For example, touching a heated cooker. Receptor: It is that sensory organ in the body that receives the stimulus. For example, on touching the heated cooker, the nerve cell in the skin will receive the stimulus and hence, skin is called the receptor.
Perception: A way of conceiving (thinking about) something
Impulse: It is the sudden electrical disturbance which runs through the nerves. For example, on touching the heated cooker, the sensation that runs through the nerves is impulse.
to a reflex action to take place is known as reflex arc. The following three neurons or nerve cells are involved in the ref lex arc: sensory neuron, interneuron or association neuron and motor Effector: It is the muscle, gland or the body neuron. part that receives the response from the brain. Sensory neurons are nerve cells within the For example, the hand muscle which is the nervous system responsible for converting ef fector will receive a command from the brain external stimuli from the organism’s environment to withdraw the hand. into internal electrical impulses. Response: The response is the change in body due to the stimulus. For example, the jerking away of the hand from the hot cooker is the response. Ref lex Action and Ref lex Arc
Ref lex actions are the reactions that take place in a split second and do not involve any major effort. They are instantaneous and do not require much thinking. For example, when your hand touches something hot, you instantly move your hand away. The path taken by an impulse that leads
Association neurons conduct impulses between neurons. The structure of motor neurons is multipolar, meaning each cell contains a single axon and multiple dendrites. This is the most common type of neuron. The cell body of the motor neuron lies inside the CNS, while the long axon goes out of the CNS. Motor neurons carry impulses from the spinal cord to the ef fectors, which in turn carry out the response. They convert the incoming sensory nerve impulse into an outgoing nerve impulse. 3
Response: The spinal cord instructs you to withdraw your hand immediately.
Receptor Sharp object Effector
Spinal cord
2
The nerve carries message to the spinal cord.
Direction of impulse 1
Stimulus: The thorn is touched.
Muscle contracts and withdraws
Fig. 4.4 Reflex action
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The hand receives the stimulus (sharp) by special receptors (F ig. 4.4) and an impulse travels through sensory neuron to the spinal cord. Here, the impulse passes through the association neuron to the motor neuron and f inally to the muscle of the arm (ef fector). The muscles of the arm get the message to contract and thus, the hand moves away from the sharp object. These actions are controlled by the peripheral nervous system and the spinal cord without the involvement of the brain. Quick Check 1 Name the following: 1. A sudden electrical disturbance that runs through the nerves. ………………………. 2. The body of a neuron: ………………………. 3. Actions that are under our control: ………………………. 4. This part of the brain consists of nerves that arise from the brain and the spinal cord: ………………………. 5. The path taken by an impulse that leads to a reflex action to take place: ………………………. 6. The cell body of the motor neuron lies inside this: ………………………. 7. This separates the axon terminal from the dendrites of the next cell: …………………….
THE ENDOCRINE SYSTEM
adolescent to an adult, and so on. The changes that take place when a person is growing up become evident after the age of 10 or 11 years. Growing up is a part of life. Children also gain emotional maturity at this stage. All these changes that occur in an adolescent are controlled by the endocrine system. Just like the circulatory system and respiratory system function, endocrine system is a complex system of organs that work together to release tiny chemical messengers located inside our body called hormones. They are so tiny that they cannot be seen with the naked eye. The endocrine system works in coordination with the nervous system to regulate dif ferent body functions such as metabolism, growth and reproduction. Hormones are secreted by endocrine glands that together make up the endocrine system. There are two types of glands present in human body which are endocrine and exocrine glands. The exocrine glands directly send the ied secretions to the organs through specif ducts. The endocrine glands are also called ductless glands because they do not have any duct and they pour their secretions (called hormones) in the bloodstream vessels through which they reach the organs. Hence, the hormones f low inside the bloodstream. Blood takes the hormones to the target sites where they must act.
A human being goes through various stages in his or her life. From a new born to an infant, The study of nervous system is called neurology. from an infant to a toddler, from a toddler to What is the study of endocrine system called? a child, from a child to an adolescent, from an ……………………………………………
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ENDOCRINE SYSTEM Pineal gland
Pineal gland Pituitary gland and Hypothalamus
Pituitary gland and Hypothalamus Thyroid and Parathyroid glands
Thyroid and Parathyroid glands
Thymus
Thymus Pancreas
Pancreas
Adrenal gland Adrenal gland
Ovary Placenta (during pregnancy)
Testicle
a. Male
b. Female Fig. 4.5 The endocrine system
Some of the important endocrine glands are: contains iodine and performs the function of thyroid gland, adrenal, pancreas and pituitary speeding up the rate of human activities. glands. icient In case the gland produces insuff thyroxine, this may lead to diseases like goitre, cretinism and myxoedema. In INFO HUB goitre, the thyroid glands enlarge and • Not all hormones come from the lead to swelling of the neck. In cretinism, endocrine system. the child may suffer from physical and • The term ‘hormone’ was coined in the early 1990s. Prior to that, they were mental retardation due to lack of iodine. In referred to as chemicals only. myxoedema, due to insuff icient iodine, there • Metamorphosis in frogs is initiated by thyroid hormone. may be a sluggishness in body along with swelling on hands and face. In case of over secretion of thyroxine, Thyroid Glands enlargement of glands, increased metabolism On either side of the windpipe, there are bilobed and heart rate along with restlessness will be glands called thyroid which is placed just below observed in the body. the larynx. This gland secretes thyroxine that 65
Adrenal glands
The adrenal glands are placed over the kidneys in a human body. They consist of two parts— central medulla and peripheral cortex. The medulla part of the adrenal glands produces the hormone called adrenaline. This is also called the f ight-or-f light hormone or emergency hormone as it prepares the human body to face any emergency. For example, in case of threat or danger, the adrenal glands secrete adrenaline that provides more energy to the body. It increases the heart beat and the respiration rate in the human body along with increase in the blood pressure and the glucose in the blood. This prepares the body to face any situation by increasing the body energy. The cortex part of adrenal gland produces many hormones but with the major one being cortisone. This hormone balances and inf luences the carbohydrates, fats, salt and water in the human body and helps it to adapt to the changing surrounding environment. Pancreas
Langerhans. The major hormones secreted by pancreas are insulin and glucagon. Insulin performs the function of reducing the extra glucose produced by pancreas. It converts glucose into glycogen (stored in liver and muscles) and also induces the cells to either burn the extra glucose to produce energy or to convert the glucose into fat. The glucose is broken down by glucagon which increases the sugar level in the body. If there is lack of insulin in the body, then it leads to diabetes. In this condition, the person feels the need for urinating again and again to wash away the extra glucose and becomes weaker and loses a lot of weight. Pituitary gland
Pituitary gland is a small peanut-sized gland which is located below the brain and secretes various hormones, some of which regulate the other endocrine glands. It is also known as the master gland as it produces some of the major hormones in the human body.
Pancreas is the digestive gland which is situated Some of the important endocrine glands in behind the stomach and contains a number human body are explained in Table 4.1. of hormone-secreting cells called Islets of Table 4.1 Endocrine glands in human body
Gland Pineal
Location
Hormone Secreted Melatonin
Deep centre of the brain Hypothalamus Base of the brain, Hormones that above pituitary stimulate the gland secretion of other hormones from pituitary gland Pituitary Middle of the Growth hormone base of the brain Thyroid-stimulating Hormone (TSH)
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Function Regulates reproductive hormones Responsible for maintaining body temperature, hunger, moods and the release of hormones from other glands. Also controls thirst and sleep.
Also called somatotropin or human growth hormone. Stimulates growth of all body tissues. Stimulates thyroid gland to secrete thyroxine
Table 4.1 (continued)
Gland
Location
Pituitary
Hormone Secreted Follicle-stimulating Hormone (FSH) Luteinizing Hormone (LH) Prolactin-Releasing Hormone (PRH) Anti Diuretic Hormone (ADH) Oxytocin
Thyroid
Parathyroid
Thymus Pancreas Adrenal glands
On either side of trachea, in front of the neck At the back of thyroid; four small-sized glands Between the lungs Below the stomach Above the kidneys
Thyroxine
Parathyroid hormone (PTH) or Parathormone Thymosin Insulin Adrenaline Cortisone
Ovaries Testes
On the both sides Oestrogen and of uterus Progesterone Beside the penis, Testosterone in scrotal sacs
Function Essential to pubertal development and for the function of women’s ovaries and men’s testes Stimulates ovulation in females; and in males, stimulates the production of testosterone Stimulates milk production in mammary glands Increases the water absorption in body by controlling the amount of water reabsorbed by the kidneys Controls social behaviour, helps in wound healing, prepares the foetus for delivery Proper development and differentiation of all cells in the body Controls calcium levels in blood
Stimulates the development of disease-fighting cells Regulates blood sugar levels Prepares the body for emergency and stress response Regulates various functions of the body, and regulates salt and water balance in the body. Responsible for female sexual characters Responsible for male sexual characters
ADOLESCENCE Now that we have studied the dif ferent types of glands, we can better understand what causes changes in our body when we reach adolescence. The onset of sexual maturity in humans is referred to as puberty. It is after this stage that an adolescent’s body becomes capable of reproduction. Girls attain puberty at the age of 10–15 years, whereas boys attain puberty slightly later than girls, that is, at the age of 12–14 years. The period of transition from a child to an adult is known as adolescence. The growing period or the spurt stops after the age of 18 years.
Baby
Pre-adolescence
Adolescence
Adult
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Physical Changes During Adolescence
The body undergoes several changes at puberty. In girls, the ovary starts producing female hormones, oestrogen and progesterone. The ovary enlarges and starts releasing eggs. Girls start getting periodic cycles during this period. In boys, the testes start releasing male hormone testosterone. This leads to complete development of testes and penis. Testes also start to produce sperms. The sex hormones lead to the secondary sexual characters: Physical appearance:
• In boys, the chest widens and shoulders broaden. Certain body parts such as arms and legs grow faster than other parts. While the genes control height, the hormones control how the height increases. • In girls, hips broaden and the breasts start developing. They also attain height during puberty. ACTION TIME
1
Data Collection and Deduction Measure your height and weight every month for about six months. Ask your friends too to do the same. Tabulate your readings. Compare it with your friend after six months. What do you conclude? Now, make a graph of Age vs Height and Age vs Weight of your friends, including yours. What do you conclude? Do you have an ideal body weight, or are you overweight or underweight?
Voice:
Changes in behaviour and pattern: Apart • In boys, the Adam’s apple situated in the neck from the physical changes, young girls and boys area starts to develop. The Adam’s apple is a change emotionally and psychologically during the adolescent stage. large voice box which starts protruding. • In girls, this is not as much developed as in All these changes occur due to hormones. boys. Hence, the boys have a guttural voice Dif ferent hormones act at specif ic sites in the human body. and girls have a high-pitched voice. Hair pattern:
Emotional Changes During Adolescence • Boys start to grow beard and moustache, and Due to hormonal changes, various emotional also pubic hair and hair in the armpits. and social changes can be observed in • Pubic hair and armpit hair start developing in adolescents. Some of them are: girls as well. Feeling oversensitive and uncertain: Sexual characters: Both males and females are • Adolescents are overly sensitive about their more aware of their own sexual appearances. appearance. Sebaceous glands: The sebaceous glands, also called the sweat glands, start secreting more • During this transition phase, they think sweat, hence increased body odour. In some about uncertain aspects of life like career and cases, the skin becomes oilier, leading to pimples. marriage. 68
Guttural: Like the sounds of frogs and crows (a heavy voice)
• They try and f igure out, how they can be unique as a person. This search can be inf luenced by gender, peer group, cultural background and family expectations.
Conf licting thoughts and mood swings:
much, taking out your stress on others, etc., are some of the unhealthy ways of coping with stress. Some of the healthy ways to tackle stress are:
• Adolescents have conf licting thoughts. They are stuck in between how they were as children and how they wish to be as they grow up. • There can be changes in the way the child interacts with family, friends and peers.
Share Your Feelings Music
Time Management
• They think more about ‘right’ and ‘wrong’. They start developing a stronger individual set of values and morals.
Laugh
Stress Management
Sleep
Nature
Change in feelings:
• Adolescents get conscious about the way they and their body is growing up. They get more conscious in the presence of peers of the same age group. Yoga
Exercise
Yoga
Meditation
Fig. 4.6 Ways to manage stress
• They start to develop and explore a sexual When we are in a constant state of stress, our identity. minds and bodies are tense and our nervous As adolescents grow older, they will develop system is heightened. Specif ic yoga poses or the skills to manage stress, but for now, they asanas can help to stimulate the relaxation must remember that they should not hesitate to response in the body. Calming and revitalising reach out (communicate) to adults and friends. poses along with controlled breathing can bring They should be explicit and open about their the mind and body to a calm and relaxed state. feelings.
Stress Management
Meditation
Meditation is a simple and fast way to reduce Stress management is all about taking charge stress. It can restore your calmness and peace of your lifestyle, thoughts, emotions, and the quickly. way you deal with problems. No matter how stressful your life seems, there are steps you can take to relieve the pressure and regain control. Stress management can make you happier, healthier and more productive. Smoking, using pills, drinking too much alcohol, withdrawing from relatives and friends, bingeing on junk food, sleeping too
Explicit: Precise and clear in communication | Bingeing: Eating immodestly
Fig. 4.7 A girl meditating
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How to meditate: simple meditation for beginners
Sit or lie comfortably. Close your eyes. Do not control the breath; simply breathe naturally. Focus your attention on the breath and on how the body moves with each inhalation and exhalation. Time management
Time management, that is, being careful about how we use our time, how we portion our time, can enhance our sense of control. The most important thing you can schedule in your day is 10 minutes to do nothing but to plan about the rest of your day or the coming day. You should also set aside some time for recreation and for rest. Sports
Participating in a sport can be a helpful way of reducing stress levels and increasing feelings of physical and mental well-being. Regular exercise should be a part of everyone’s routine. Hobbies
A hobby is a great stress reliever. Focusing on a hobby diverts your attention from all that you have been dealing with in your day. It is a fun way to take a break from life’s daily demands. When searching for a hobby, consider your interests, your lifestyle, and your budget. F ind something that interests you and that you want to continue learning about, become more prof icient in, and maintain a passion for. What is your favourite pastime or hobby?
Rational thinking Rational thinking is an important tool for stress management. Most of the stress is caused
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Recreation: An activity that refreshes and recreates
due to impractical decisions taken by us. But if we take our decisions based on facts, think through situations practically, we will arrive at sound decision. A sound decision is a stress-free decision. Personal Hygiene
Balanced diet: A growing child needs a good diet for the proper and better growth. The diet of a growing child should include all the basic food components in correct amounts. A diet that gives your body the nutrients it needs to function properly and correctly is called balanced diet. A balanced diet contains proteins, fats, carbohydrates, vitamins and minerals. This is essential both for the physical and for the mental growth of the child. Small amounts of all the essential minerals are necessary for the body. Consuming excess of junk food can lead to various disorders such as obesity, diabetes, etc. Always watch what you eat. If the energy intake is more than energy liberated, weight is gained. However, if energy intake is less than energy liberated, weight is lost. Physical exercise: Physical activities, such as playing outdoor games, jogging and cycling are also necessary for the child’s growth.
Personal hygiene: One must also keep himself/ herself neat and clean. Bathe regularly, wash hair regularly, and also clean the pubic area and the armpits. If care is not taken, it can result in bacterial infection. Females, however, should take extra care of hygiene during the menstrual cycle.
Quick Check 2
Functions of Blood
The blood performs a number of important functions for the body. They are as follows: The hormone secreted by: 1. Blood helps in carrying oxygen and carbon 1. Pineal gland: …………………………… dioxide between the respiratory organs and 2. Pituitary gland: ……………………….. tissues. 3. Ovaries: ……………………………….. 2. It helps in transporting the nutrients and 4. Testes: ……………………………………… water to all parts of the body from the alimentary canal. 3. The blood helps in carrying the stored food CIRCULATORY SYSTEM and vitamins to the tissues or organs where The circulatory system in humans consists of they are generally needed. blood, blood vessels and heart. 4. It helps in transporting the waste products from the tissues to the excretory organs and regulates the water balance. 5. It helps in regulating the temperature of an organism and distribution of heat equally Heart in all parts of the body. 6. It contains antibodies to f ight against the infections in the body. Veins 7. It prevents excessive bleeding in case of accidents by forming blood clots. 8. It carries hormones from the glands to the parts where they are needed for action. Name the following:
Arteries
Fig. 4.8 Circulatory system
Blood
Blood is a f luid connective tissue which contains specialised cells. It is a red-coloured f luid that f lows inside the blood vessels and carries the food throughout the human body. An average adult normally has about 5 litres of blood.
INFO HUB The flow of blood and its force against the wall of the blood vessel is called blood pressure. It is the pressure exerted by the blood on the artery walls. The blood pressure is supposed to be at its maximum when the heart contracts and when the heart relaxes, it is supposed to be less. The instrument used to measure blood pressure is known as sphygmomanometer. Anxiety or eating food with fats is responsible for affecting the blood pressure. The normal blood pressure is 120/80 mm of Hg. If the pressure is higher than 140/90 mm of Hg, then it is called hypertension or high blood pressure. If the pressure is lower than the normal, then it is called hypotension or low blood pressure.
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Blood Vessels
Between the heart and the pericardium, there is The blood circulates in our body through a a f luid which protects the heart from external network of blood vessels. There are three kinds jerks and is a shock absorber. This f luid is called the pericardial f luid. of blood vessels: arteries, veins and capillaries.
Arteries: These blood vessels carry the blood from INFO HUB the heart to the different parts of the body. They The heart of human beings weighs only have thick and strong walls which can take about 225–340 grams. It can pump about the force of the blood pumped from the heart. 16,360 litres of blood in 24 hours. The arteries carry oxygenated blood from the heart to the various organs of the body, except the pulmonary artery which carries the Lymphatic System deoxygenated blood from the heart to the lungs. The lymphatic system protects us from Aorta is the largest artery in the body. infection and disease. It consists of lymphatic Veins: The veins carry blood from the dif ferent vessels, lymph nodes and f luid lymph nodes. parts of the body to the heart. The veins have much The lymphatic system is a part of the human thinner walls as compared to the arteries. The immune system. blood does not f low with pressure in the veins because by the time the blood reaches the veins, the pressure from the heart becomes lesser. The veins contain valves which prevent the blood from f lowing backwards. All the veins carry deoxygenated blood except the pulmonary vein which carries oxygenated blood from the lungs Lymphatic vessels to the heart. The coronary arteries branch of f into smaller arteries which supply oxygen-rich blood to the entire heart muscle. Capillaries: These are very thin blood vessels which are connected to the veins and the arteries. The capillaries are present in all the tissues of the body but found more in the metabolically active parts of the body like the brain and the lungs.
Lymph nodes
Heart
The heart is a f ist-shaped muscular organ which is located in the chest. It is protected by a sac of membrane in a ribcage called the pericardium. 72
Fig. 4.9 Lymphatic system
INFO HUB Lymphatic system forms a parallel circulatory system in the human body.
ventricle and prevents backf low of blood between the same.
The two auricles are separated by inter-auricular septum and the two ventricles are separated by inter-ventricular septum. This results in the The lymph is a clear, straw-coloured watery f luid blood not being able to mix, with the right side which f ilters from the blood capillary walls into being totally separated from the left side of the the intercellular spaces or the tissue spaces. The heart. function of the lymph is to transfer the water, salts and other waste substances from the cell Right Auricle to the blood. The cells take in food which is The deoxygenated blood is received by the collected in the lymph capillaries. The lymph right auricle through two veins—superior vena vessels are found wherever the blood vessels cava and inferior vena cava. The functions of are a part of the circulatory system. The lymph these two veins is that the superior vena cava f luid passes through the lymph nodes which are collects and brings in the deoxygenated blood connected by a network of lymph vessels. The from the parts of the body above the heart and nodes are found throughout the human body. the inferior vena cava collects and brings the deoxygenated blood from the parts of the body The Human Heart below the heart. The heart is divided into four chambers or cavities. The two upper chambers are the left In the upper part of the right atrium of the heart, and right auricles or atria. The two lower ones there is a bundle of specialised cells. These cells are called the left and right ventricles. The create rhythmic impulses and set the pace for ventricles have much thicker walls than the auricles. pumping of blood. These cells are referred to as They have a special kind of muscles called the pacemaker cells. They directly control the heart cardiac muscles. The normal human heart beats rate. They make up the cardiac pacemaker or the natural pacemaker of the heart. In most human 72 times per minute. beings, the group of pacemaker cells in the The blood f lows in one direction, that is, from sinoatrial (SA) node is the natural pacemaker. the auricle to the ventricle. It cannot f low backwards from the ventricle to the auricle. Right Ventricle There are two types of valves that regulate It receives the deoxygenated blood from right the f low of the blood from the auricle to the auricle. Right ventricle then sends deoxygenated ventricle: blood to the lungs for oxygenation through the 1. The tricuspid valve allows the blood to pulmonary artery. f low between the right auricle and right The pulmonary trunk is a major blood vessel of ventricle and prevents backf low of blood the human heart that originates from the right between the same. ventricle. It then branches into the right and 2. The bicuspid valve allows the f low of left pulmonary arteries, which lead to the lungs. blood between the left auricle and left 73
Left Auricle
The oxygenated blood is received by the left auricle from the lungs through pulmonary veins. Left Ventricle
The left ventricle receives the blood from left auricle and sends oxygenated blood through aorta to the dif ferent parts of the body.
The f low of blood to the pulmonary artery and the aorta from the ventricles is also regulated by valves. The pulmonary semilunar valve guards the opening of right ventricle into the pulmonary artery and the aortic semilunar valve guards the opening of left ventricle into the aorta.
Aorta Superior vena cava
Right pulmonary arteries
Left pulmonary arteries
Left pulmonary veins
Right pulmonary veins
Left atrium
Right atrium
Mitral valve Aortic valve
Pulmonary valve
Triscupid valve Left ventricle Inferior vena cava Right ventricle Fig. 4.10 The human heart
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Septum
INFO HUB The beating of the heart can be felt in the arteries of the wrist as a regular beat or jerk called the pulse. It is the throbbing of the arteries because of the flow of blood in them. The pulse is actually a wave against the walls of the blood vessels. The wall of the aorta expands and contracts with contents of the ventricle. Each beat of the heart causes a pulse within the arteries that can be felt when one keeps a finger lightly on the radial artery on the wrist. In a human body, higher pulse rate indicates hypertension or fever in the human body whereas low pulse rate indicates poor functioning of the heart.
Blood Circulation The blood circulates in our body by the pumping action performed by the heart. In the human beings, the circulation cycle works in two ways: pulmonary (lung) circulation and systemic (body) circulation.
Pulmonary (Lung) Circulation: In this process, the right ventricle sends deoxygenated blood to the lungs for oxygenation through pulmonary artery and the left auricle receives oxygenated blood from the lungs through pulmonary vein.
Systemic (Body) Circulation: In this process, the right auricle receives deoxygenated blood from the dif ferent parts of the body and the left ventricle sends oxygenated blood through aorta to dif ferent parts of the body. Double circulation
The majority of mammals (including humans) utilise a double circulatory system. This means that we have two loops in our body in which blood circulates. One is oxygenated, meaning oxygen-rich, and the other is deoxygenated,
which means it has little to no oxygen, but a lot of carbon dioxide. This whole process of blood circulation can be explained as follows: In blood circulation, the deoxygenated blood is collected from the dif ferent parts of our body through two major veins called the vena cava and is brought to the right auricle. After the contraction of the right auricle, the blood is pushed into the right ventricle. When the right ventricle contracts, then the tricuspid valve prevents the blood from f lowing back into the right auricle. Upper part of the body Vena cava
Aorta
Vena cava
Heart
Capillaries
Lower part of the body Fig. 4.11 Path of blood circulation
From the right ventricle, the blood gets pumped into the pulmonary artery which carries the blood into the lungs. There is an exchange of gases, that is, oxygen and carbon dioxide in the lungs. Once the deoxygenated blood goes into the lungs, the carbon dioxide from the deoxygenated blood is carried out by the lungs and the oxygen from the lungs gets mixed with the blood. This oxygenated blood is then carried into the left auricle by the help of the pulmonary vein. When the left auricle 75
contracts, the blood enters the left ventricle. However, when the left ventricle contracts, then the bicuspid valve prevents the blood from f lowing back into the left auricle. The left ventricle opens into the large artery called the aorta. The blood is pumped into the aorta and it is thereby carried out to dif ferent parts of the body. Once the oxygen gets consumed by the human body, the deoxygenated blood again comes back into the right auricle. This is then carried into the right ventricle for being transported back into the lungs again and likewise, the process continues.
Conditions related to the functioning of the heart Palpitations
A heart palpitation is the sensation by a person of having hard, rapid or irregular heartbeats or a combination of these sensations. The patient may show the following symptoms: • Shortness of breath
an emergency condition. The person collapses suddenly, does not breathe properly and is unresponsive. Smoking, obesity, sedentary lifestyle, high blood pressure or drinking too much alcohol can cause cardiac arrest. Hypertension
Hypertension, also known as high blood pressure, is when the pressure of the blood being pumped through your arteries is higher than it should be. Hypertension is often called the ‘silent killer’. INFO HUB The systolic reading of 120 mm of Hg refers to the pressure as the heart pumps blood around the body. The diastolic reading of 80 mm of Hg refers to the pressure as the heart relaxes and refills with blood. During hypertension, both the systolic and diastolic readings are constantly high.
Blood Groups
The kind of blood type can vary from person to person. The red blood cells in the blood contain a • Chest pain number of protein molecules called the antigens. • Fainting The antigens are foreign substances in the body Palpitation can be caused due to: of humans which initiate the production of antibodies by the human immune system. The • Vigorous physical activity antibodies are chemical substances which are • Taking cold, cough and asthma medications • Hormonal changes due to menstruation, made by the human body in response to the foreign substances or antigens. Thus, based on the pregnancy and menopause antigens and antibodies, blood groups also dif fer. • Fever The ABO blood grouping system was • Strong emotions like stress and anxiety, etc. originally introduced by Karl Landsteiner in Cardiac Arrest 1900. According to this system, there are four A cardiac arrest happens when a person’s heart major kinds of blood groups which depend stops pumping blood around the body. It is on the presence of antigens and antibodies • Dizziness
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within them. There are basically two kinds of antigens: antigen A and antigen B and two kinds of antibodies: A and B. The blood groups can have either antigen or antibodies or can have both. Based on these, the table below shows the dif ferent types of blood groups. Table 4.2 Combination of blood groups
Blood group
Antigen and antibody combinations
A
Antigen A; Antibody B
B
Antigen B; Antibody A
AB
Antigen A and B; No Antibodies
O
No Antigens; Antibodies A and B
The person having blood group ‘O’ can give blood to a person with any blood group and is called the universal donor. A person with blood group ‘AB’ can receive any type of blood and is called the universal recipient. A person with blood group ‘A’ can receive blood from persons with blood group ‘A’ and ‘O’. A person with blood group ‘B’ can receive blood from persons with blood group ‘B’ and ‘O’.
ACTION TIME
INFO HUB • The positive and negative conditions of blood groups are based on the presence or the absence of another factor called Rh-factor. If the Rh factor is present, then the blood group is positive (Rh+ve) and if it is not present, then it becomes negative (Rh-ve). • The pus flowing from an infected wound is a collection of dead white blood cells. It is a colourless fluid that flows from a wound. It gets build up due to an infection from the body’s immune system. One needs a course of antibiotics to destroy the germs or bacteria that help in formation of the pus.
Quick Check 3 Name the following: 1. The two upper chambers of the heart: ………………………. 2. This system protects us from infections and diseases: ………………………. 3. Lung circulation is also called: ………………………. 4. This valve allows the blood to flow between the right auricle and right ventricle. ………………………. 5. A fist-shaped muscular organ: ……………………….
2
Visit a nearby hospital. Go into the pathological laboratory. Observe how the blood is taken and the methods used for determining the blood group of the patient. One can also observe how blood transfusion takes place. You can also ask questions to the doctors regarding different blood tests that reveal different infections like aids, typhoid, diabetes and more. Make a report.
k e y T e rm s Coordination: The interaction and interrelation between the various activities in the body of a living being that take place internally and externally. It can be of two types—nervous coordination and chemical coordination. Neurons: Also called nerve cells. They are the smallest structural and functional units of the nervous system. Nerve: A bundle of axons or nerve fibres which are enclosed in an elongated sheath or casing
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Stimulus: The change that happens outside the body in the environment and which causes a change in the body Receptor: The sensory organ in the body that receives the stimulus Impulse: The sudden electrical disturbance which runs through the nerves Effector: The muscle, gland or the body part that receives the response from the brain Response: The change in body due to the stimulus Reflex actions: The reactions that take place in a split second and do not involve any major effort Reflex arc: The path taken by an impulse that leads to a reflex action to take place Sensory neurons: Nerve cells that are responsible for converting external stimuli from the organism’s environment into internal electrical impulses Association neurons: Nerve cells that conduct impulses between neurons Motor neurons: Convert the incoming sensory nerve impulse into an outgoing nerve impulse Puberty: The onset of sexual maturity in humans Adolescence: The period of transition from a child to an adult Auricles: The two upper chambers of the human heart Ventricles: The two lower chambers of the human heart
q u i c k not e s ✶✶ The coordination of the nerves and the brain is part of the nervous coordination. ✶✶ Nerves are of three kinds—sensory, motor and mixed. ✶✶ The central nervous system consists of the brain and spinal cord. ✶✶ Peripheral nervous system consists of nerves that arise from the brain and the spinal cord. Depending
on where they arise, the nerves that arise from the brain are known as cranial nerves and spinal nerves. ✶✶ Motor neurons are multipolar, meaning each cell contains a single axon and multiple dendrites. This is
the most common type of neuron. ✶✶ Endocrine system is a complex system of organs that work together to release tiny chemical
messengers located inside our body called hormones. Hormones are secreted by endocrine glands. ✶✶ Stress management is all about taking charge of your lifestyle, thoughts, emotions, and the way you
deal with problems. ✶✶ It is important to maintain personal hygiene during adolescence. ✶✶ The circulatory system in humans consists of blood, blood vessels and heart. ✶✶ There are three kinds of blood vessels—arteries, veins and capillaries. ✶✶ The lymphatic system helps us protect from infection and disease. ✶✶ The tricuspid valve allows the blood to flow between the right auricle and right ventricle and prevents
backflow of blood between the same. ✶✶ The bicuspid valve allows the flow of blood between the left auricle and left ventricle and prevents
backflow of blood between the same. ✶✶ A heart palpitation is the sensation by a person of having hard, rapid or irregular heartbeats or a
combination of these sensations. ✶✶ There are four major kinds of blood groups in humans.
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run-through I. Very Short Answer Questions. A. Tick (✓) the correct option. 1. Reflex actions are in response to……………….. stimuli. a. external
b. internal
c. both a and b
d. none of these
2. Finger-like extensions in a neuron: a. Cytons
b. Dendrites
c. Cell bodies d. Axons
3. The spinal cord lies within the: a. Vertebral column
b. Skull
c. Neuron d. Nerve
4. This is the largest part of the brain: a. Medulla oblongata
b. Spinal cord
c. Cerebrum
d. Cerebellum
5. The muscle, gland or body that receives response from the brain: a. Receptor
b. Stimulus
c. Impulse
d. Effector
6. How many pairs of spinal nerves are there in the peripheral nervous system? a. 30
b. 31
c. 32
d. 33
7. Which of the following is a growth hormone? a. Somatotropin
b. Gonadotropin
c. Melatonin d. Thyroxine
8. TSH stands for: a. Thyroid Sensory Hormone
c. Thyroxine Stimulating Hormone
b. Thyroid Stimulating Hormone d. Thyroxine Sensory Hormone
9. The onset of sexual maturity in humans is called …………………… . a. Adolescence
b. Deduction
c. Spurt d. Puberty
10. This is not a way to manage stress:
b. Bingeing on junk food
c. Managing time
d. Playing outdoor games
a. Meditating
11. The flow of blood and its force against the wall of the blood vessel is called blood …………………… . a. pressure
b. volume
c. vessel d. circulation
B. State whether the following statements are True or False. 1. The myelin sheath is enveloped by axon in a neuron.
………………………….
2. Mixed nerves contain both sensory and motor fibres.
………………………….
3. The cerebellum is positioned behind the cerebrum.
………………………….
4. Exocrine glands are also called ductless glands.
………………………….
5. Pancreas regulates blood sugar levels in the human body.
………………………….
6. A hobby is a stress giver.
………………………….
7. Veins carry blood from the heart to different parts of the body.
………………………….
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8. The lymph is a clear, straw-coloured watery fluid.
………………………….
9. Myxodema is caused due to insufficient sodium in the body.
………………………….
C. Fill in the blanks. 1. The …………………………. (tricuspid/biscuspid) valve allows the flow of blood between the left auricle and left ventricle. 2. The ………………… (ABO/ABZ) blood grouping system was introduced by Karl Landsteiner. 3. The person having blood group ………………………. (AB/O) is called the universal donor. 4. …………………….. (Blood/Gland) help(s) in carrying oxygen and carbon dioxide between the respiratory organs and tissues. 5. Sebaceous glands are also referred to as …………………….. (sweet/sweat) glands. 6. Thymus gland is present in between the ………………….. (kidneys/lungs). 7. The secretions of ……………………………. (endocrine/exocrine) glands are called hormones. 8. Medulla oblongata is also referred to as the …………………………… (brain stem/brain pipe).
D. Complete the concept map. Glands
Exocrine glands
They pour their secretions (hormones) in the bloodstream vessels through which they reach the organs.
Pineal
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Melatonin
II. Short Answer Questions. A. Distinguish between: 1. Central nervous system and Peripheral nervous system 2. Effector and Receptor 3. Brain and Spinal cord 4. Exocrine and Endocrine glands 5. Thyroid and Parathyroid glands 6. Arteries and Veins 7. Right auricle and Left auricle 8. Pulmonary and Systemic circulation
B. Give reasons. 1. How can we feel the beating of the heart in the arteries? 2. The brain is covered by the skull. 3. Pituitary gland is called the master gland. 4. The body starts to change at the onset of puberty. 5. It is important to manage stress.
C. Answer the following questions. 1. What are the two types of coordination in the human body? 2. Name the three types of nerves. 3. What is a neuron? 4. What is reflex arc? How is it useful for our body? 5. Why are endocrine glands called ductless glands? 6. Write a short note on adolescence. 7. What is blood? What are its functions? 8. Name the types of blood vessels. 9. Draw and explain about motor neuron.
III. Long Answer Questions. 1. Explain reflex action with the help of a suitable diagram. 2. List the functions of various hormones in our body. 3. State the physical changes that are observed during adolescence. 4. What emotional changes are observed during adolescence? 5. How can we manage stress? Explain. 6. What is double circulation? Explain with the help of a diagram. 7. List and explain about the different blood groups.
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8. List the conditions related to the functioning of the heart. 9. What is the importance of thyroid glands in our body?
IV. Challenge 1. What will happen if there are no valves in the heart? 2. What will happen if we have no reflex action? 3. List any three reflexes you feel in day-to-day life. 4. What will happen in the absence of semilunar valves?
V. Enrichment A. The 4 As of Stress Management
Avoid
Alter
Unnecessary stress
The situation
Adapt
To the situation
Accept
The things you can’t change
Take help from your teacher and do a role play to explain the 4 As. Present it in the school assembly.
B. Model Making: Make a model of the following using waste materials. 1. Neuron
2. Human heart
(This can be done as a group activity.)
C. Research and Report. Who is a pathologist? Search the library books and the Internet. Make a onepage report in your notebook.
ScientificQue s t Conditioned Reflex Some action or feeling that you learn to do in response to a specific situation or stimulus is called a conditioned reflex. Explain this using an example. You may take help from your teacher, library and the Internet.
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10
Across
p u
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Down
83
P I C T UR E S UR V E Y Label the different glands in the following diagram.
Which hormone is released in response to stress in our body?
84