Guided teaching hours: 4 hours

Transcription

1 Cell division Chapter overview Guided teaching hours: 4 hours In this chapter, students will learn about the process of cell division and after finishing the chapter should be able to describe the three overall stages of the cell cycle. Students will develop have an understanding of mitosis as a stage within the cell cycle, but do not need to know about the different phases of the mitosis stage. They should be able to state the genetic material in the nucleus is doubled before the cell divides into two. Along with cell division, students will study cell differentiation, and students should be able to make connections between cell differentiation and the specialised cells and adaptations they studied in Chapter B1 Cell structure and transport. Students will also learn that stem cells are undifferentiated cells that have the potential to become a specialised cell within an organism. Students should be able to describe some potential uses of stem cells, as well as the disadvantages and objections to the use of stem cells, particularly in relation to medical treatments. This resource sheet may have been changed from the original. 1

2 Lesson.1 Cell division WS: The nucleus of a cell contains chromosomes made of DNA molecules. Each chromosome carries a large number of genes. In body cells the chromosomes are normally found in pairs Cells divide in a series of stages called the cell cycle. Students should be able to describe the stages of the cell cycle, including mitosis. During the cell cycle the genetic material is doubled and then divided into two identical cells. Before a cell can divide it needs to grow and increase the number of sub-cellular structures such as ribosomes and mitochondria. The DNA replicates to form two copies of each chromosome. In mitosis one set of chromosomes is pulled to each end of the cell and the nucleus divides. Finally the cytoplasm and cell membranes divide to form two identical cells. Students need to understand the three overall stages of the cell cycle but do not need to know the different phases of the mitosis stage. Cell division by mitosis is important in the growth and development of multicellular organisms. Students should be able to recognise and describe situations in given contexts where mitosis is occurring. State that human body cells have 46 chromosomes and gametes have 23. State that mitosis is a stage in cell division. State the meaning of most of the key words mitosis, chromosomes, gene, gametes. Explain why chromosomes in body cells are normally found in pairs. Describe situations where mitosis is occurring. Use the key words to describe the process of mitosis. Explain why genetic material must be doubled during mitosis. Explain in detail what happens at each stage of the cell cycle. Use the key words to write detailed explanations of why mitosis is an important process in living things and how characteristics are inherited. Cell key words (10 min) Bump up your grade sheet where students review their understanding from KS3 of the key words nucleus, gene, DNA, and chromosome and develop their definitions. They are also introduced to the key word mitosis. Cell division (10 min) Draw an image representing a single zygote (fertilised egg) on the board. Ask students to use what they recall from KS3 to draw images to show the stages before and after the egg is fertilised. Discuss their ideas, drawing out the process of fertilisation before and cell division after. Introduce the key word mitosis as a stage of cell division. Mains Chromosomes (10 min) Refer students to student book section The information in the cells. Ask students questions about the numbers of chromosomes in body cells and gametes, and why they are found in pairs in body cells. Observing mitosis (20 min) Show students a diagram of the cell cycle. Ask them to estimate the percentage of time involved in each of the three stages, calculate how long the interphase stage would take if the whole cycle took 24 hours, and suggest why the interphase stage is the longest. Students then complete the practical where they use light microscopes to observe prepared slides showing mitosis. Ask them to spot cells at different stages and draw examples. They can use Figure 3 from the student book to help them. Mitosis (10 min) Students use the interactive to match the key words from this lesson to their meanings and then carry out a cloze exercise about mitosis. This resource sheet may have been changed from the original. 2 Bump up your grade: Cell key words Practical: Observing mitosis Interactive: Mitosis

3 Cell cycle length (5 min) Tell the class that, on average, human cells take 24 hours to divide. Ask them to calculate how long it takes for one cell to form a group of 64 cells. Lesson.2 Growth and division Practical: Cauliflower cloning Interactive: Cell differentiation Students should be able to explain the importance of cell differentiation. As an organism develops, cells differentiate to form different types of cells. Most types of animal cell differentiate at an early stage. Many types of plant cells retain the ability to differentiate throughout life. Define the terms growth and differentiation. State why plant clones are genetically identical to each other. Attempt to clone a plant by using apparatus correctly. Human life (10 min) Show students an image of an embryo containing a few cells and an image of a very old person. Ask them to design a flow chart to show what happens to the cells of a person as they grow older. Discuss their ideas and explain that in development from an embryo to an adult, cell division is used for growth (increase in size) as well as for repair and replacement. In adults, it is mainly just used for repair and replacement. Introduce the word growth to mean a permanent increase in size. In mature animals, cell division is mainly restricted to repair and replacement. As a cell differentiates it acquires different sub-cellular structures to enable it to carry out a certain function. It has become a specialised cell Stem cells from meristems in plants can be used to produce clones of plants quickly and economically: Rare species can be cloned to protect from extinction. Crop plants with special features such as Describe the importance of cell differentiation in multicellular organisms. Explain how using tissue culture creates a clone of a plant. Attempt to clone a plant by using apparatus correctly and following safety rules. Growth in plants and animals (5 min) Show the class an image of a tall tree and a human. Ask them to discuss in pairs how the growth of a plant and a human are the same and how they are different. Make sure students understand that in plants growth is due to cell elongation and division, whereas in humans it is just cell division. Main Cauliflower cloning (40 min) Tell the class that plant cells contain This resource sheet may have been changed from the original. 3

4 disease resistance can be cloned to produce large numbers of identical plants for farmers. Compare and contrast differentiation in plants and animals. Explain why it is easier to clone a plant than an animal. Explain and carry out a practical accurately and safely in order to successfully clone a plant. undifferentiated cells in tissues called meristems. They will follow a procedure to clone a new cauliflower plant using these cells. Students work in pairs and follow the practical sheet to carry out the task. They must pay careful attention to working accurately and safely in order to ensure cloning is successful. Students then answer questions about differentiation and cloning in plants. Differentiation (10 min) Ask students to return to the flow chart they designed in the starter Human life and add in information about where differentiation occurs and what it is used for. Cell differentiation (5 min) Interactive where students select the correct word for each gap in a paragraph about cell differentiation and then sort statements into plant and animal cell groups. Lesson.3 Stem cell A stem cell is an undifferentiated cell of an organism which is capable of giving rise to many more cells of the same type, and from which certain other cells can arise from differentiation. Students should be able to describe the function of stem cells in embryos, in adult animals and in the meristems in plants. Stem cells from human embryos can be cloned and made to differentiate into most different types of human cells. Stem cells from adult bone marrow can form many types of cells including blood cells. Meristem tissue in plants can differentiate into State that a stem cell is a cell that is not differentiated. State that plant stem cells can be used to create clones. State ways in which stem cells can be used to treat medical conditions. Describe differences between embryonic and adult stem cells. Explain why plant clones are produced in agriculture. Describe how stem cells can be used to treat medical conditions. Differentiation (5 min) Ask students to write down a definition of the term differentiation. Gather ideas to come to an agreed meaning and write this on the board. Discuss why cells differentiate and remind students that undifferentiated cells are known as stem cells. Plant copies (10 min) Remind students of the practical they did in Topic.2 where they cloned a cauliflower (this is an ideal opportunity to check on how the practical is doing). Ask students to discuss in pairs reasons why people might want to clone plants. Gather together the ideas as a class. Main Stem cells (15 min) Remind students about how embryonic stem cells have the potential to differentiate into any type of cell. Students then use information from the student book to help them Activity: Writing scientifically with stem cells Interactive: Stem cells WebQuest: Embryonic stem cell research This resource sheet may have been changed from the original. 4

5 any type of plant cell, throughout the life of the plant. Knowledge and understanding of stem cell techniques are not required. Treatment with stem cells may be able to help conditions such as diabetes and paralysis. In therapeutic cloning an embryo is produced with the same genes as the patient. Stem cells from the embryo are not rejected by the patient s body so they may be used for medical treatment. The use of stem cells has potential risks such as transfer of viral infection, and some people have ethical or religious objections. Stem cells from meristems in plants can be used to produce clones of plants quickly and economically. Rare species can be cloned to protect from extinction. Crop plants with special features such as disease resistance can be cloned to produce large numbers of identical plants for farmers. Explain why embryonic stem cells are particularly useful for treating medical conditions. Explain how stem cells can be used to treat medical conditions. answer questions about stem cells. Writing scientifically with stem cells (25 min) Provide students with example articles on stem cells. Alternatively, provide students with short examples of science articles printed from websites or cut out from magazines. Ask them to discuss in pairs what they think about the articles (Did they capture their attention and hold it? Did they explain the science well? Did they leave them wanting to know more?). Go through with the class the main points on how to write a science article. Students then research how stem cells are used to help medical conditions and use the information to write their own article on stem cells. This activity can be extended to a whole lesson. Peer assessment (10 min) Students use the checklist on the activity sheet to peer assess the articles written in Main 2 and give useful feedback. Stem cells (10 min) Interactive here students match the correct words to statements and then select words to fi ll in the gaps in a paragraph about stem cells. This resource sheet may have been changed from the original. 5

6 Lesson.4 Stem cell dilemmas A stem cell is an undifferentiated cell of an organism which is capable of giving rise to many more cells of the same type, and from which certain other cells can arise from differentiation. Students should be able to describe the function of stem cells in embryos, in adult animals and in the meristems in plants. Stem cells from human embryos can be cloned and made to differentiate into most different types of human cells. Stem cells from adult bone marrow can form many types of cells including blood cells. Meristem tissue in plants can differentiate into any type of plant cell, throughout the life of the plant. Knowledge and understanding of stem cell techniques are not required. Treatment with stem cells may be able to help conditions such as diabetes and paralysis. In therapeutic cloning an embryo is produced with the same genes as the patient. Stem cells from the embryo are not rejected by the patient s body so they may be used for medical treatment. The use of stem cells has potential risks such as transfer of viral infection, and some people have List some arguments for and against the use of stem cells. Verbally communicate simple ideas during a group discussion. Describe what therapeutic cloning can be used for. Explain the reasons for ethical and religious objections to use of stem cells in medicine. Verbally communicate wellconstructed arguments. Explain the process of therapeutic cloning. Evaluate the use of stem cells in medicine. Clearly communicate strong, wellresearched arguments in a persuasive manner. Stem cell decision (10 min) Tell students to imagine that a close friend or family member has been diagnosed with diabetes and has to inject themselves with insulin every day for the rest of their lives. There is a new treatment available using stem cells grown from embryos. Would they advise them to use the treatment? Ask the class to discuss in small groups what information they would need to find out before they could make a decision. Listen to ideas from the class and discuss that there are many possible risks to the treatment and these have to be weighed up alongside possible benefits. Also, some students may mention religious or ethical objections to using embryonic stem cells. Ethical dilemmas (5 min) Read out a series of statements: Organ transplants using donated organs from people who have died. Organ transplants from living donors. Taking the morning-after pill. Using contraception. Using unwanted embryos for medical research (they will be destroyed after use). Testing new medical treatments on healthy volunteers. Testing new medical treatments on animals. After each statement ask students to rate out of 5 how they feel about it, with 1 being very comfortable and 5 being totally against it. Discuss individual views and elicit that different people have different viewpoints for different reasons. Before a decision can be made these have to be taken into account. Main Viewpoints (40 min) Assign students to the different roles shown on the activity sheet and ask them to read through their character s This resource sheet may have been changed from the original. 6 Activity: Viewpoints Bump up your grade: The future of stem cell research Interactive: Stem cell dilemmas

7 ethical or religious objections. Stem cells from meristems in plants can be used to produce clones of plants quickly and economically. Rare species can be cloned to protect from extinction. Crop plants with special features such as disease resistance can be cloned to produce large numbers of identical plants for farmers. thoughts on the use of stem cells and prepare a 60-second speech arguing their character s viewpoint. Ask students to form groups containing all the roles and to each present their viewpoint. As a class, ask groups for the main points they found out during their discussion and record these on the board. As a class, discuss all of the points they have found, then have students individually write their own conclusions on the ethics of stem cell research. The future of stem cell research (10 min) Bump up your grade worksheet where students review the process of therapeutic cloning and the ethical difficulties involved, evaluating the potential benefits and possible drawbacks. Stem cell dilemmas (5 min) Interactive here students match the correct words to statements and then select words to fill in the gaps in a paragraph about stem cells. This resource sheet may have been changed from the original. 7