Chapter 1: Cells – the Building Blocks of Life
1.1 Introduction When and how to use these pages The Introduction in the Student Book indicates some of the ideas and skills in this topic area that students will already have met from KS2 or from previous KS3 work, and provides an indication of what they will be studying in this chapter. Ideas you have met before is not intended to be a comprehensive summary of all the prior ideas, but rather to point out a few of the key ones and to support the view that scientific understanding is progressive. Even though students might be meeting contexts that are new to them, they can often use existing ideas to start to make sense of them. In this chapter you will find out indicates some of the new ideas that the chapter will introduce. Again, it isn’t a detailed summary of content or even an index page; its purpose is more to act as a ‘trailer’ and a way of generating interest among students. The outcomes, then, will be recognition of prior learning that can be built on and stimulation of students’ interest in finding out more. There are a number of ways these two pages can be used. You might, for example:
• Use the Ideas you have met before as the basis for a revision lesson as you start the first new topic. • Use Ideas you have met before as the centre of spider diagrams, to which students can add examples, experiments they might have done previously or things they found interesting.
• Make a note of any unfamiliar/difficult terms and return to these in the relevant lessons. • Use ideas from In this chapter you will find out to ask students questions such as: • Why is this important? • How could it be used? • What might we be doing in this topic?
Overview of the chapter In this chapter, students will learn about the structure and function of specialised plant and animal cells, organisation in multicellular organisms, different types and adaptations of unicellular organisms and how plants and humans are adapted to reproduce. They will explore linked processes, including diffusion, pollination, seed dispersal, menstruation and fertilisation. They will consider environmental factors in discussing the role of insects and reasons for their demise. This chapter offers opportunities for students to become familiar with the use of microscopes. They are encouraged to use 3-D models to explain the structures of different cell types. They will plan to collect evidence and present data on pollen-tube growth and evaluate the effectiveness of seed-dispersal mechanisms.They will explore validity and reliability of evidence in several contexts, including how different substances affect the developing foetus. They will discuss advantages and disadvantages of adapations in plants, encouraging reasoning, analysis and evaluation.
Obstacles to learning Students may need extra guidance with the following terms and common misconceptions:
• Nucleus A common misconception is that the nucleus in a cell is the same as the nucleus of an atom. • Pollination and fertilisation These may be used interchangeably by students to mean the same process. • Seed dispersal Students may think that this only occurs by wind. They may also get confused between seeds and pollen.
• Puberty Students may think this consists of set changes at particular times. • Growth A common misconception is that cells get bigger and bigger.
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Chapter 1: Cells – the Building Blocks of Life
Topic title
Overarching objectives
2
Historical ideas about living things
Cells as the fundamental unit of living organisms, including how to observe and record cell structure using a light microscope
3
Comparing plant and animal cells
Cells as the fundamental unit of living organisms, including how to observe and record cell structure using a light microscope The functions of the cell wall, cell membrane, cytoplasm, nucleus, vacuole, mitochondria and chloroplasts The similarities and differences between animal and plant cells
4
Describing cells
The functions of the cell wall, cell membrane, cytoplasm, nucleus, vacuole, mitochondria and chloroplasts The similarities and differences between animal and plant cells
5
Understanding unicellular organisms
The structural adaptations of some unicellular organisms
6
Understanding diffusion
The role of diffusion in the movement of materials in and between cells Diffusion in liquids and gases driven by differences in concentration
7
Understanding organisation in multicellular organisms
Hierarchical organisation of multicellular organisms: from cells to tissues to organs to systems to organisms
9
Comparing flowering plants
Reproduction in plants, including flower structure, wind and insect pollination
10
Knowing how pollination leads to fertilisation
Reproduction in plants, including flower structure, wind and insect pollination, fertilisation
11
Understanding the challenges facing pollinators
The importance of plant reproduction through insect pollination in human food security
12
Understanding how seeds are dispersed by the wind
Reproduction in plants, including seed and fruit formation and dispersal
13
Understanding how fruits disperse seeds
Reproduction in plants, including seed and fruit formation and dispersal, including quantitative investigation of some dispersal mechanisms
14
Understanding the male reproductive system
Reproduction in humans (as an example of a mammal), including the structure and function of the male and female reproductive systems
15
Understanding the female reproductive system and fertility
Reproduction in humans (as an example of a mammal), including the structure and function of the male and female reproductive systems, menstrual cycle (without details of hormones), gametes, fertilisation, gestation and birth
16
Learning about changes in puberty
Reproduction in humans (as an example of a mammal), including the menstrual cycle (without details of hormones)
17
Learning how a foetus develops
Reproduction in humans (as an example of a mammal), fertilisation, gestation and birth
18
Understanding factors affecting a developing foetus
Reproduction in humans (as an example of a mammal), to include the effect of maternal lifestyle on the foetus through the placenta
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Chapter 1: Cells – the Building Blocks of Life
1.2 Historical ideas about living things Lesson overview Learning objectives • Summarise some historical ideas about living things. • Explain how evidence can change ideas. • Select evidence to support or disprove ideas. Learning outcomes • Describe what people used to think about living things and how their ideas changed. [O1] • Describe how early experiments were carried out and how new evidence changed people's ideas. [O2] • Consider the quality of the evidence in different investigations and how good evidence can be used to refute or support ideas. [O3]
Skills development • Thinking scientifically: understand how theories develop • Working scientifically: interpret evidence • Learner development: ask questions Resources Worksheet 1.1.2 (the final page copied onto card) Common misconceptions Not all living things are made from cells. Key vocabulary organism, conclusion, microscope, cell, evidence
Teaching and learning Engage • Introduce the students to the theory of ‘spontaneous generation’, first proposed by Aristotle (see the Student Book), and ask them to discuss what investigation(s) they could carry out to prove or disprove this theory. Ask them to consider what evidence they would find from their investigations. How would they make this evidence reliable? Collect feedback and discuss their ideas. Is it harder to prove or disprove the theory through their investigations? [O1&3]
Challenge and develop • Show the experimental set-up carried out by Redi (Figure 1.1.2b in the Student Book). Ask the students to discuss what Redi set out to do and what he found out using the questions in the Student Book, and to identify different aspects of his investigation. [O2]
• Ask them to suggest why people still believed in the spontaneous generation theory for 200 years afterwards, despite the evidence from Redi’s investigation. Establish that evidence needs to be reliable in order to support or refute a theory, and discuss why the evidence from Redi’s investigation was not reliable. [O2&3]
• Tell the students about the Pasteur investigation 200 years after Redi. Ask them to compare and contrast the two investigations. A range of questions about the nature of the investigations could be asked, such as 'What scientific question was being investigated?', 'What was the independent variable in the investigations?', ‘Which variables were being controlled to make the test fair?' [O2&3]
• Show the students a timeline of the development of the microscope (Figure 1.1.2c in the Student Book). Discuss the impact of the microscope on ideas about living things. [O1&2]
Explain • Ask the students to complete their own timeline of ideas, with annotations to explain the evidence that changed people's ideas using the Student Book to help. [O1&2] Key Stage 3 Science Teacher Pack 1
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Chapter 1: Cells – the Building Blocks of Life
Consolidate and apply • Pair talk Ask the students to use the evidence cards from Worksheet 1.1.2 to decide which evidence can be used to support the theory of spontaneous generation, and which evidence refutes the theory. [O2&3] Higher-attaining students could rank the evidence in order of strength and justify their ideas.
Extend • Ask students able to progress further which of the scientific studies they have learned about today had the most impact on ideas about living things and why. [O1, 2&3]
Plenary suggestions Summarise learning Ask the students to work in pairs. Providing at least one example, one person tells their partner how they have met all the learning outcomes.
Answers to Student Book questions 1. 2. 3. 4. 5. 6. 7.
a) support b) support c) disprove For example swallows emerging from rafters; baby owls flying out of barns; woodlice coming out of wood Does dead meat produce flies? He used the same amount of dead meat; jars of the same size; left them for the same amount of time. The sealed jars did not produce flies; if the theory had been correct, all the jars would have produced flies. Life was only found in the bottles that had been left open to the air; life had come in from the air, not from the broth. Pasteur's; because he used many bottles and kept them for over a year; this makes his investigation more reliable. He also had bottles especially made, so there was no chance of any air getting in. 8. People had believed in spontaneous generation for a long time; ideas are hard to change. Also Redi had carried out only one investigation, so the evidence was not very reliable. 9. We have discovered that living things are very complex; we have begun to understand how organisms work and how cells work. (This has been used to make discoveries about how to cure different cancers.)
Answers to Worksheet 1.1.2 1. a) cards 1, 5 and 6 b) cards 2, 3, 4 and 7 2. 1 Y People would think the corn stacks produced the mice. 2 N If spontaneous generation were true, the broth would have produced bacteria. 3 N When lambs are born, people would see them as coming from the mothers. 4 N Cells are very complicated and couldn’t just come from inanimate objects. 5 Y People thought the eels could have come from the pools. 6 Y People thought the dead meat produced the flies. 7 N The dead meat should have produced the flies if the theory is true. 3. a) Accurate – the evidence is close to the truth. Valid – the evidence has been produced by a fair test and answers the scientific question being asked. Reliable – you can trust the evidence because the same results are given by many repeats. b) Accurate?
Valid?
Reliable?
1
Y
N
N
2
Y
Y
N
3
Y
Y
Y
4
Y
Y
Y
5
Y
N
N
6
Y
N
N
7
Y
N
N
c) Card 1 describes the least reliable and valid evidence. To improve the quality of the evidence, several corn stacks should be tested, making sure they are all the same and there is nothing else but corn in them to start with. To prove the corn has made the mice, the stacks should be sealed so nothing can get in or out.
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Chapter 1: Cells – the Building Blocks of Life
1.3 Comparing plant and animal cells Lesson overview Learning objectives • Develop models to explain the differences between animal cells and plant cells. • Record evidence using a microscope. • Communicate ideas about cells effectively using scientific terminology. Learning outcomes • Label an animal cell and a plant cell. [O1] • Compare and contrast the similarities and differences between plant cells and animal cells, and use a microscope independently to make observations. [O2]
• Describe the functions of the nucleus, cell membrane, mitochondria, cytoplasm, cell wall, vacuole and chloroplast. [O3]
Skills development • Thinking scientifically: use models • Working scientifically: record evidence • Learner development: communicate effectively Resources materials and equipment as detailed in the Technician’s notes; overhead projector; Worksheet 1.1.3a; Worksheet 1.1.3b; Practical sheet 1.1.3a; Practical sheet 1.1.3b; Technician’s notes 1.1.3 Common misconceptions Cells are two-dimensional, inert objects. The nucleus of a cell and the nucleus of an atom are the same. Key vocabulary nucleus, cytoplasm, cell membrane, mitochondria, cell wall, vacuole, chloroplast
Teaching and learning Engage • Show the students the images of plant and animal cells in Figures 1.1.3a and b in the Student Book. Ask them to identify three facts about each image. [O1]
• Demonstrate how to use a microscope. Ask the students to make observations of a variety of different objects using the microscope – for example newspaper print, hair, a coin, a paper towel (see Technician’s notes 1.1.3). Ask them to discuss their observations and the importance of the microscope in scientific discoveries. [O2]
Challenge and develop • Ask half the students to follow the instructions on Practical sheet 1.1.3a and make up a slide of a cheek cell; ask the other half to follow instructions on Practical sheet 1.1.3b to make up a slide of an onion cell. Ask them to draw accurate diagrams of both types of cells on their sheets. [O1&2]
• Refer the students back to the different parts of the animal cell and the plant cell from the Student Book. Ask them to relate these to the corresponding parts of the diagrams of their slides, and to label them. If possible, link up a microscope to the overhead projector and point out the different parts from the prepared slides. [O1&2]
• Provide half of the students with the descriptions of different parts of an animal cell, and the other half with the descriptions of plant cells, found on Worksheet 1.1.3a. Ensure that they are clear about what the descriptions say. Provide the students with a range of different materials to select from. Ask them, in pairs, to make a model of their cells from the descriptions. [O1&2]
• Pair swap Ask one from each pair to join with someone who made the other model. Each should explain their model to the other. [O1&2] Key Stage 3 Science Teacher Pack 1
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Chapter 1: Cells – the Building Blocks of Life
Explain • Select different students to show their cell models and to explain each part to the class. They should be able to justify why they chose certain materials to represent particular parts. Ask them to identify the features in a plant cell that are not in an animal cell. [O1&2]
Consolidate and apply • Provide the students with Worksheet 1.1.3b. Ask lower-attaining students to complete task 1, naming each structure of the cell. Middle-attaining students should complete tasks 1 and 2. [O1]
• Higher-attaining students need to complete all three tasks explaining how the three cell parts are adapted to carry out their particular jobs. [O2&3]
Extend • Ask the students to research how cells evolved in the first place. They should prepare a one-minute talk to deliver to the class. [O3]
Plenary suggestions What am I? Play ‘What am I?’ Think of a part of a cell, and select students to provide a question to guess the part of the cell. Only ‘yes’ or ‘no’ answers can be given.
Answers to Student Book questions 1. 2. 3. 4. 5. 6. 7.
under a microscope yes nucleus; mitichondria oxygen; glucose; water, carbon dioxide; urea cell wall; vacuole plant cell; it has more structures in it To provide them with extra strength and protection – many animals eat plants; to help with photosynthesis – chloroplasts absorb light.
Answers to Worksheet 1.1.3b 1. Refer to Figures 1.1.3b and 1.1.3c in the Student Book. 2. N = nucleus; C = chlorophyll; V = vacuole; C = cytoplasm; C = cell wall; C = cell membrane three structures in both: cell membrane; cytoplasm; nucleus 3. a) Very thin to help small substances transfer in and out quickly. b) Made of cellulose to give it strength. c) Packed with chlorophyll, which absorbs sunlight.
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Chapter 1: Cells – the Building Blocks of Life
To make good progress in understanding science students need to focus on these ideas and skills: Students who are making modest progress will be able to:
Students who are making good progress will be able to:
Students who are making excellent progress will be able to:
Recognise and label normal and specialised animal and plant cells; use a microscope to make observations.
Describe the functions of the nucleus, cell membrane, mitochondria, cytoplasm, cell wall, vacuole and chloroplast.
Compare and contrast the similarities and differences between normal and specialised animal and plant cells.
Describe unicellular organisms – including yeast, bacteria, euglena, paramecium and amoeba – as being either prokaryotes or eukaryotes.
Describe the function of specialised parts of different unicellular organisms.
Explain how different structures help organisms to survive.
Recognise the role of diffusion in living organisms.
Describe the process of diffusion, and name the materials needed by and those removed from the cell.
Explain the factors that affect diffusion.
Put the terms cell, tissue, organ and organ system in order of hierarchy, naming some common tissues, organs and organ systems in humans.
Explain the terms cell, tissue, organ and organ system and the function of all the main organ systems in the body.
Describe some benefits and disadvantages of multicellular organisms, compared to single-celled organisms.
Describe the role of different parts of the flowering plant in reproduction.
Explain the differences in insectpollinated and insect-pollinated plants.
Discuss the strengths and weaknesses of wind-pollinated and insect-pollinated plants.
Recognise different seed-dispersal methods by the structures of the seeds.
Identify key variables that need to be controlled when investigating the effect of seed design on seed dispersal.
Explain the advantages and disadvantages of different seeddispersal mechanisms.
Name the main parts of the male and female human reproductive systems.
Describe the structures and functions of the main parts of the male and female human reproductive systems; describe how fertility problems may arise.
Explain how the male and female reproductive structures are designed for fertilisation; describe methods to combat infertility.
Recognise changes that occur during adolescence.
Describe how the menstruation cycle works.
Explain how and why some problems occur with menstruation.
Identify substances passed on from a mother that will either help or harm her developing foetus.
Describe the structures and functions of different parts of a pregnant uterus, describing how substances pass into and from a developing foetus.
Explain how a pregnant uterus is different from a normal uterus, including the impact of different substances on the health and development of a foetus.
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