1. B2a Tp2 Divide and Develop Revision

2. Understand the meaning of growth in terms of increase in size, length, dry/wet weight. Understand how cell division, elongation and differentiation contribute to the growth and development of an organism.

3. What is growth? Growth is an irreversible increase in the size or mass of an organism as it develops. Different organisms grow at different rates, and these growth rates vary at different stages of development. Mammalian development begins in the womb. This is called the gestation period and is different for each species. The rate of growth in the womb is fixed but changes during development.

4. Growing fast

5. A slow start For the first week, humans don’t actually grow – the fertilized egg cell (zygote) splits in two every day to make a bundle of smaller cells. cell division After about 1 week, the zygote is called an embryo.

6. Exponential growth

7. What are stem cells? The first cells are stem cells. These are unspecialized cells capable of developing into many different types of cell. If stem cells continued to divide as they were, humans would end up as a large jelly-like blob! Stem cells found in embryos are called embryonic stem cells and develop into all the different types of cell in the body.

8. Changing cells When the embryo contains about 500 cells, the cells stop being the same and they stop getting smaller with each division. They start to differentiate into different types of cell. At this point, stem cells no longer form two new stem cells when they divide. Instead, one of the two daughter cells becomes a progeny or tissue cell. stem cell tissue cellstem cell

9. Becoming specialized Tissue cells continue to divide and differentiate, each time becoming more and more specialized. Some will become nerve cells, others will become blood cells, muscle cells, bone cells, etc. nerve cells red blood cells stem cell tissue cells cardiac muscle cells

10. Describe mitosis as the division of a cell to produce two nuclei with identical sets of chromosomes

11. Divide and grow Most animals and plants start off life as just a single cell, but grow to become adults containing billions and billions of cells. How does one cell become billions and billions of cells? The type of cell division that makes animals and plants grow is called mitosis. In mitosis, a parent cell divides into two identical daughter cells. These daughter cells divide in two, and so on. Mitosis is also the way in old and damaged cells are replaced. mitosis parent cell daughter cells

12. One of a kind? The two daughter cells produced by mitosis are genetically identical to the parent cell. What does this mean? All the genes and chromosomes from the parent cell must be copied and passed on to the daughter cells. Normally, a cell only contains one copy of each chromosome, but before dividing a cell must duplicate all its chromosomes. This means that all the genes will also be duplicated.

13. condensed chromosome Duplicating chromosomes A cell’s chromosomes are usually long, thin strands. Just before the cell divides, however, the chromosomes become shorter, thicker and more visible. They are said to condense. Each chromosome duplicates and becomes two strands, each one called a chromatid. The two chromatids are joined at the centromere. centromere chromatid

14. What are the stages of mitosis? Once the chromosomes have duplicated, mitosis takes place. This is a continuous process but can be divided into several parts: The chromosomes align in the middle of the parent cell. The two chromatids in each chromosome are pulled apart into separate halves of the cell. The cell splits in two to produce two daughter cells, each containing the same chromosomes. Mitosis involves copying a cell and its chromosomes exactly, so it is sometimes called copying division. Each chromosome replicates so it contains two identical chromatids.

15. What happens during mitosis?

16. The stages of mitosis

17. Chromosomes during mitosis

18. Human beings have been breeding plants and animals for thousands of years. Farmers picked the best milk cows to produce calves, so that they would inherit their milk-producing genes. Other farmers collected seeds from the best wheat plants, so that the next generation would also be good plants. But what do we mean by ‘best’ and ‘good’?

19. Explore the evidence that selective breeding can be used to improve the quality and yield of products and offspring

20. Early genetic engineering People have been doing a simple form of genetic engineering for thousands of years. This is called selective breeding. Selective breeding, or artificial selection, is a process where people try and improve plants and animals by selecting and breeding only those that have desirable characteristics. For example, a farmer might choose the two largest cattle in his herd and breed them together so that the offspring will be even bigger and produce more meat.

21. Choose a cow!

22. Examples of selective breeding Many plants and animals are selectively bred to improve their characteristics. What are some examples? Breeding sheep to produce more wool. Breeding wheat to produce more grain. Other examples include breeding racing horses to become faster, and breeding dogs to obtain unique characteristics (e.g. bulldog, greyhound, Chihuahua). Breeding tomatoes to have more flavour.

23. Discuss the potential benefits and ethical dilemmas posed by advances in genetic modification

24. Crops can be given extra genes for new and useful characteristics. They are genetically modified (GM). What characteristics might be useful in crops? pest resistance frost resistance herbicide resistance drought resistance longer shelf life disease resistance What is Genetic Modification?

25. Genetic engineering is about changing the DNA of a living thing to change its characteristics. Living things naturally create useful products. Genetic engineering can be used to make living things produce other, more valuable, products. For example, yeast naturally converts sugar into carbon dioxide and alcohol, and is used in baking and brewing. Yeast can also be genetically engineered to produce vaccines for human diseases.

27. Interpret data

28. Thinking skills Look at the table. What does it tell us?

29. Tables present data and help us to answer questions and see patterns in results. What questions could you ask about this table that other people in your class could answer?

30. a) Describe what has happened to the temperature of the world since 1860.  The temperature of the world has increased by 0.7 0 C.

31. …discuss the risks associated with later embryonic developments

32. ADVANTAGES Hundreds of ideal offspring produced every year from the best animals.Hundreds of ideal offspring produced every year from the best animals. The sperm and egg donors can produce eggs and sperm year round.The sperm and egg donors can produce eggs and sperm year round. Economically worth while.Economically worth while.DISADVANTAGES Reduced gene pool.Reduced gene pool. Animals could be vulnerable to disease. Animals could be vulnerable to disease. What is a clone?

33. Cloning in the media