Biology
CELL BIOLOGY
1
IDEAS YOU HAVE MET BEFORE:
IN THIS CHAPTER YOU WILL FIND OUT ABOUT:
ALL LIVING ORGANISMS ARE MADE OF CELLS. • • • •
HOW HAVE SCIENTISTS DEVELOPED THEIR UNDERSTANDING OF CELL STRUCTURE AND FUNCTION?
Cells are the building blocks of life. Cells contain specialised structures. Organisms such as bacteria are unicellular. All plants and animals are multicellular.
IN MULTICELLULAR ORGANISMS CELLS BECOME SPECIALISED. • Specialised cells have a particular job to do. • Specialised cells are organised into tissues, tissues into organs, and organs into body systems.
• The structures inside cells do different jobs within the cell. • Cells can be studied using different types of microscopes. • The cells of bacteria are different from the cells of plants and animals.
brain thyroid trachea lung heart liver stomach large intestine small intestine bladder
ORGANISMS OBTAIN ENERGY BY THE PROCESS OF RESPIRATION. • The energy that is released drives all the processes necessary for life. • Most organisms respire by aerobic respiration, using oxygen. • Some cells or organisms can survive without oxygen. They respire anaerobically.
HOW DO WE DEVELOP INTO A COMPLEX ORGANISM FROM JUST A FERTILISED EGG CELL? • The body’s cells divide and the newly formed cells are identical to the existing cells. • Cells differentiate to become specialised, and specialised cells are organised. • When cell division accelerates out of control, cancer develops. • Cells that are unspecialised in the embryo, and cells that remain unspecialised in us as adults, are called stem cells. • Stem cells could be used to treat certain conditions and diseases that are currently untreatable.
HOW DO ORGANISMS OBTAIN THEIR ENERGY FROM FOOD? • Anaerobic respiration: when some organisms run out of oxygen, they can respire without it. • Many microorganisms can respire anaerobically, as can the muscles of mammals for short periods.
WHY IS IT IMPORTANT TO STUDY MICROORGANISMS, AND HOW DO WE GROW THEM IN THE LAB AND COMMERCIALLY? MICROORGANISMS CAN HELP TO KEEP US HEALTHY AND PROVIDE US WITH FOOD. • Microorganisms produce important food products by fermentation. • Bacteria in the gut are important in keeping us healthy.
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• The biochemistry of fermentation is involved in the production of alcoholic drinks and bread. • Lab techniques are used to grow, or culture, microorganisms. • Microorganisms reproduce, and the number of bacteria produced can be estimated. • Tests can show how effective antibiotics, antiseptics and disinfectants are at inhibiting the growth of bacteria.
Cell Biology
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Biology
Increasing food production Learning objectives: • explain how factors that increase food production can be controlled • evaluate the benefits of manipulating the environment to increase food production • understand and use the inverse square law in the context of light intensity and photosynthesis.
Key words hydroponics yield inverse square law
Higher tier only
Greenhouses Growing crops in greenhouses gives a large yield for a given area. This is intensive farming. Conditions in the greenhouse can be controlled to optimise the rate of photosynthesis. Greenhouses protect plants from weather conditions and from being damaged or eaten by animals. shades removed from ceiling to allow maximum light
Farmers need to grow large fruits and vegetables without excessive leaf or root production. By optimising photosynthesis, and reducing effects of limiting factors, farmers can increase yields of crops. Using technology, commercial greenhouses increase yields by over twenty times, compared with traditional farming. Glucose produced by photosynthesis that is not used for respiration, or stored, in the form of starch, is converted to other essential molecules such as cellulose, and amino acids and proteins. Mineral ions are required for these conversions. The mineral ions provided to plants can be optimised using a technique called hydroponics. Plants are grown in nutrient-rich liquid medium, which can be formulated for the type of plant, supported on a material such as rock wool.
Farmers use their knowledge of the limiting factors of photosynthesis to increase crop yields. How can this be done? How do they change the factors?
ventilation
What are the benefits and drawbacks of changing conditions inside a greenhouse?
Inverse square law Figure 2.17 Why are dull cold days in winter not good for growing plants?
Figure 2.18 A greenhouse system
• Sunlight heats up the inside of greenhouses, causing the temperature to rise. • A carbon dioxide source can be used to increase the concentration of the gas. • Paraffin heaters are used in greenhouses. As the fuel inside them burns, they produce carbon dioxide. They can also be used to increase the temperature on cooler days and nights. • Watering systems deliver a regular supply of water. • Blinds can be used to control the amount of light. • Humidifiers are used to add moisture to the air. 1
Why do many greenhouses have vents in the roof?
2
Explain why paraffin heaters are used in greenhouses.
3
How do greenhouses increase yield?
AQA GCSE Biology: Student Book
Key information
• Nutrients are monitored and concentrations adjusted as needed. Remember that • Temperature is controlled by sensors to within 0.1°C. greenhouses optimise • Weather detection systems monitor external conditions and carbon dioxide adjust vents and blinds to suit. concentrations, light levels, • Floors are covered in white plastic to reflect light. water levels, temperature • The glass used has a low iron content to ensure maximum and nutrient availability. light levels and even the metal supports are as thin as possible. • Special lights are used to increase the hours of light. These are switched off for about 7 hours, allowing plants to transport the glucose that has been made.
heater
watering system
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Figure 2.19 Hydroponics is growing plants in mineral nutrient solutions, without soil
Computer systems control conditions.
4 carbon dioxide source
2.6
Optimising conditions
As the distance between the light source and a photosynthesising plant increases, the light intensity will decrease. This is described as being an inverse relationship. Light intensity obeys the inverse square law. The inverse square law states that if the light distance is doubled, the light intensity decreases by the square of the distance. For example, if the distance between the light source and the plant is doubled, the light intensity is quartered (see Figure 2.20). 5
I 9
I LIGHT INTENSITY 4
A
I A
light source
AREA
A A
The energy twice as far away is spread over four times the area, etc.
A
A AREA A
1d
A
2d DISTANCE
A
A A A
A A
3d
Figure 2.20 Light intensity obeys the inverse square law: if the distance between the light source and the plant is doubled, the light intensity is quartered.
Look back at Amy and Laura’s data on page 63. Draw a graph of rate of photosynthesis against 1/d2.
Google search: 'conditions in greenhouses'
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Biology
Exploring the heart
• The pulmonary artery transports deoxygenated blood from the right ventricle to the lungs.
Key words
Learning objectives: • describe the structure and function of the heart • identify the functions and adaptations of the parts of the heart • explain the movement of blood around the heart.
aorta atrium (plural: atria) coronary artery pacemaker vena cava ventricle
Ventricles have thicker walls than atria because they pump blood further. The left ventricle pumps blood around the body. It has a thicker wall than the right ventricle, which only pumps blood to the lungs. Valves between the atria and the ventricles prevent the backflow of blood. They open to let blood through and then shut.
pulmonary artery
to lungs
3.14
to body aorta
from body
from lungs
vena cava pulmonary vein right atrium left atrium right ventricle
3
Active or larger animals need a transport system with a pump. This is to maintain a constant supply of materials to meet the demand of all cells throughout the body, and to remove waste.
4
Describe how the atria and ventricles move blood through the heart.
coronary arteries
The heart has two pumps (a double circulation) that beat together about 70 times every minute of every day.
In the second century, Galen thought blood was made in the liver. He said it flowed round the body, but was used as fuel for the muscles. Galen also thought there were holes in the septum, which allowed blood to flow from one side of the heart to the other. In the seventeenth century, Galen’s ideas were disproved by William Harvey, who explained heart structure and described the blood vessels. valve closed
right atrium
Figure 3.34 Why does the heart need an oxygen supply?
Blood from the body contains very little oxygen and enters the heart at the right atrium, passes into the right ventricle and is pumped to the lungs to be oxygenated.
2
Describe how blood flows through the heart.
The parts of the heart The heart has four main blood vessels: • The pulmonary vein transports oxygenated blood from the lungs to the left atrium. • The aorta (main artery) transports oxygenated blood from the left ventricle to the body. • The vena cava (main vein) transports blood from the body to the right atrium.
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oxygenated blood
deoxygenated blood
left atrium
valve open
Blood from the lungs contains oxygen and enters the heart at the left atrium. It passes into the left ventricle and is pumped out to the body.
What is the function of the heart?
oxygenated blood
valve left ventricle
Explaining blood flow
The heart is made of muscle. Heart muscle continually contracts and relaxes. It uses a lot of energy. Heart muscle receives oxygen and glucose for respiration from the blood brought by the coronary artery.
1
deoxygenated blood
Figure 3.36 Why does the heart need two pumps?
The heart
Each pump has an upper chamber (atrium) that receives blood and a lower chamber (ventricle) that pumps blood out. Both atria fill and pump blood out at the same time, as do both ventricles. The natural resting heart rate is controlled by a group of cells located in the right atrium that act as a pacemaker.
Describe the functions of the different chambers of the heart.
Left atrium
C Ventricles contract from the bottom upwards which forces blood into the pulmonary artery or aorta.
B
left ventricle
Atria contract at the same time which forces blood into both ventricles.
Figure 3.37 The cardiac cycle 5
Explain the sequence of contractions and valve openings as blood passes through the heart.
6
If a coronary artery supplying the left ventricle becomes blocked, what effect does this have on the functioning of the heart? Explain your answer.
The body
Figure 3.35 Blood flow through the heart
The complete cardiac cycle normally takes 0.8 seconds.
right ventricle
valve shut
Left ventricle
Did you know?
Heart relaxes and blood enters both atria.
The lungs
Right ventricle
Atria receive blood, ventricles pump it out.
valve open
A
Right atrium
Key information
Google search: 'heart structure'
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Biology
Check your progress
Worked example
You should be able to:
Viruses are pathogens that cause many diseases. Babies and children are vaccinated to protect them from many viruses.
■■describe the major causes of ill health
explain how diseases and ➞ ■■lifestyle factors affect health
■■recall a number of interacting factors which cause different diseases
■■describe different types of tumours
■■explain how risk factors are
➞
linked to an increased rate of some non-communicable diseases
➞
■■describe lifestyle changes to reduce cancer risk
■■describe the symptoms of
some viral, bacterial, fungal and protist diseases
■■describe how the body protects itself from pathogens
■■recall why vaccinations are used
➞ ➞
➞
immune system
explain how vaccinations ➞ ■■trigger an immune response
■■recall some plant diseases and
➞
➞
factors and increased rates of disease
■■evaluate evidence linking smoking and cancer
antibiotic-resistant bacteria
2
They produce poisons.
a One type of tumour is known as benign. Name the other type of tumour and explain how it is different from a benign tumour.
Cancer tumour spreads through the body. b Name a risk factor for lung cancer.
Smoking
■■explain the use of
➞
It makes antibodies.
d Why do pathogens make us feel ill?
explain the limitations of ➞ ■■antibiotics monoclonal antibodies in identifying plant pathogens
A weak form of the virus.
c What does the vaccine do in the child’s body?
bacterial and viral diseases ■■evaluate control measures for malaria ■■explain the specificity of antibodies
■■explain the impact of
They cannot kill them.
b What is in a vaccine?
evaluate the global use of ➞ ■■vaccinations
■■explain the identification
and symptoms of some plant diseases ■■explain some plant defences
■■compare and contrast
➞ ■■explain the role of the
a Why are antibiotics not used to kill viruses in the body?
control of different diseases
➞
1
■■evaluate evidence linking risk
■■describe the transmission and
■■describe the use of antibiotics ➞ ■■explain how antibiotics and and painkillers painkillers treat disease plant defences
evaluate graphical data ➞ ■■about lifestyle and health
3
The correct answer is that viruses live inside cells, where they are protected from the action of antibiotics. Correct answer identified, although ‘weak form’ could be improved by replacing it with ‘inactive or dead form’. This is inaccurate. White blood cells/lymphocytes make antibodies. This is partially correct, but the answer should also include the fact that pathogens damage cells. Incorrect tumour type identified. Correct answer is malignant tumour, but the difference is correct. Correct answer identified
a Describe how malaria is spread by mosquitoes.
Mosquitoes suck the blood of an infected person. b Explain how malaria is controlled by insecticide.
Answer should also include how the mosquito then passes the protist pathogen/Plasmodium to an uninfected person.
Insecticide kills eggs. Answer should mention mosquito eggs, and also include that mosquitoes lay their eggs in water.
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Worked example
167
Biology HIGHER TIER ONLY
KEY WORDS
pituitary gland pituitary gland
FSH LH oestrogen progesterone
Learning objectives: • describe the roles of hormones in sexual reproduction • explain how hormones interact in the menstrual cycle.
secondary sex characteristics testosterone follicle
The menstrual cycle is concerned with the maturation of an egg every month and preparing follicle stimulating luteinising follicle stimulating luteinising hormone (FSH) hormone (LH) the uterus to receive that egg if it is fertilised. This could result in(FSH) pregnancy. hormone hormone (LH) ovary
These hormones interact with each other during the menstrual cycle. ovary ovulation ovulation oestrogen progesterone oestrogen progesterone
Thickness of uterus FSH and LH in ng/cm3
Four hormones control the menstrual cycle: • follicle stimulating hormone (FSH) causes eggs to mature in the ovaries • luteinising hormone (LH) stimulates the release of an egg from an ovary • oestrogen and progesterone maintain the lining of the uterus. 3 4
208
Which four hormones control the menstrual cycle? Which hormones maintain the lining of the uterus?
AQA GCSE Biology: Student Book
24th
Oestrogen in ng/cm3
2nd
menstruation
3rd 4th
egg dies if not fertilised
uterus lining is shed
23rd
5th 6th
22nd 21st
ovulation
uterus lining starts to repair and grow again
20th continues to thicken
8th
10th
egg is released from ovary
18th 17th
11th
12th 16th
15th
14th
200
en str og
400
pituitary gland
1
6 4
stimulation
2
LH FSH 0 5 inhibition inhibition ovary 0 2 4 6 8 10 12 148 16 18 20 22 24 26 28 6 8 4 2 leads to eggs ovary ovulation maturing in tissues follicle 3
0
repair of wall of uterus
13th
Figure 5.52 The menstrual cycle lasts approximately 28 days, but this is highly variable
progesterone progesterone
8 8 6 6 4 4 2 2 0 18 20 22 24 26 280 18 20 22 24 26 28
COMMON MISCONCEPTION
ovary empty follicle 7 progesterone
Don’t confuse the pituitary hormones FSH and LH, which are regulatory, with the reproductive hormones produced by the ovaries (oestrogen and progesterone) and testes (testosterone).
9 development and maintenance of lining of uterus in preparation for pregnancy
Figure 5.54 The roles of the hormones as the cycle progresses are: 1 FSH is secreted by the pituitary gland.
9th
19th
600
oestrogen
7th
uterus lining
FSH
oe
1st day
25th
The menstrual cycle The menstrual cycle is the reproductive cycle in women, which – by convention – starts with a period (menstruation), if the woman is not pregnant.
28th
26th
What happens in males and females under the influence of these hormones?
200
menstruation
800 800 600 600 400 400 200 200 0 0 0 2 4 6 8 10 12 14 16 0 2 4 6 8 10 12 14 16
Figure 5.53 The menstrual cycle is controlled by four main hormones Last day
27th
menstruation 400
Progesterone in ng/cm3
2
Give the main reproductive hormones in males and females.
LH
0 0 2 04 26 48 610 81210 1412 16 14 18 16 2018 2220 2422 26 24 28 262 284 6 Time (days) progesterone 800 8
In the male, testosterone is the main reproductive hormone. It is produced by the testes. It stimulates sperm production. 1
600
Ovulation
Oestrogen is the main female reproductive hormone that is produced at this time. It is produced by the ovaries. Eggs start to mature in the ovaries and are released, at approximately one every 28 days. This process is called ovulation.
800
3 3 Progesterone inin ng/cm Progesterone ng/cm
Oestrogen, progesterone and testosterone are steroid hormones. Steroid hormones also help to control glucose and protein metabolism, and water balance.
Secondary sex characteristics develop as our bodies produce reproductive hormones at puberty.
Ovulation
ovulation oestrogen progesterone
Did you know?
Ovulation Ovulation
ovary
800 800 600 LH 600 LH 400 400 FSH 200 FSH 200 0 0 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28
oeoe strst ogrog enen
follicle stimulating luteinising hormone (FSH) hormone (LH)
3 3 FSH and LHLH inin ng/cm FSH and ng/cm
Our first exposure to sex hormones is not at puberty, but as a foetus. In the presence of male sex hormones (which needs a Y chromosome), male characteristics develop; in their absence, the foetus becomes female.
3 3 Oestrogen inin ng/cm Oestrogen ng/cm
pituitary gland
Reproductive hormones
5.19
Menstrual cycle hormones
Ovulation Ovulation
Human reproduction
7 … leads to the secretion of progesterone by the empty follicle that contained the egg.
2 FSH causes the eggs to mature in the ovaries.
8 Progesterone inhibits the release of LH and FSH.
3 FSH stimulates the ovaries to produce oestrogen.
9 Progesterone maintains the lining of the uterus during the second half of the menstrual cycle, in readiness for receiving a fertilised egg.
4 & 5 Oestrogen inhibits further release of FSH and stimulates release of LH. 6 LH triggers ovulation – the release of the mature egg from the ovary – and … 5
Which two hormones repair the uterus after menstruation and encourage its growth?
6
Suggest which hormones are involved in negative feedback.
Google search: 'FSH, LH and ICSH, oestrogen, progesterone'
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Biology
End of chapter questions
b What is the median result?
Getting started 1
1 Mark
i 6 ii 5 iii 4 iv 8
The following diagram shows the location of the major endocrine glands. 6
A
Look at the photograph of the plant. Explain why it is growing in this way.
2 Marks
B
C
ovaries – in female D testes – in male
Going further 7
a Which letter labels the thyroid gland?
1 Mark
2
What is the ruler-drop test used to measure?
1 Mark
3
Describe the recommendations a doctor would make to a patient diagnosed with Type 2 diabetes.
4 5
How should the person being tested hold the ruler at the beginning of the test?
8
2
4
3
3
4
6
5
5
6
7
7
4
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8
Which hormone leads to oestrogen production by the ovaries?
1 Mark
9
Short-sightedness is a condition when people struggle to see objects at a distance. Give a cause of short-sightedness.
1 Mark
Scientists investigating the effect of gravity on a plant placed it on an instrument called a clinostat. A clinostat rotates, so the plant is exposed to gravity equally from all directions. The effects of gravity are neutralised. direction of turn
clinostat
Mean
a Calculate the mean distance dropped by the ruler.
2 Marks
10 1 Mark
Distance ruler dropped in cm
1
• speed of response.
2 Marks
The table below shows some results from the ruler-drop test: Test number
• type of message
1 Mark
b W hich letter represents the gland where, if it produces insufficient hormone, diabetes results?
Compare the nervous and endocrine systems according to their:
1 Mark
Describe and explain what would happen to the plant after several days on the clinostat.
3 Marks
End of Chapter Questions
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