Doc Brown's GCSE OCR Gateway Science-Biology Revision Notes

OCR GCSE Gateway Additional Science Biology Module B3 Living And Growing

Unit-Item B3d Cell division

1. Appreciate that as living things grow, the number of cells in them increases bringing significant advantages, and requires the development of complex organ systems.

2. In this unit you studied the two ways cells divide, mitosis and meiosis, and the differences between these types of cell division.

3. Possible practical and research activities you engaged in may have included

   • Viewed software simulations and video clips which show cell division

   • Examining prepared microscope slides to show cell division.

   • Preparing a stained microscope slide of a root tip squash to show mitosis (eg garlic or hyacinth).

   • Preparing a stained microscope slide of a root tip

   • Examining a bull’s sperm using a microscope.

   • Examining a hen’s egg to show the large amount of stored food.

   • Examining pollen using a microscope.

   • Using models to illustrate cell division, using wool or plasticine.

   • Using bacterial or yeast growing kits.

4. Be able to describe the difference between simple organisms which are unicellular and more complex organisms which are multicellular.

5. Know that most body cells contain chromosomes in matching pairs.

6. Be able to explain why the chromosomes have to be copied to produce new cells for growth.

7. Know that this type of cell division is also needed for:

   • a) replacement of worn out cells

   • b) repair to damaged tissue

   • c) asexual reproduction.

8. Know that in sexual reproduction gametes join in fertilisation.

9. Know that gametes have half the number of chromosomes of body cells.

10. Understand that in sexual reproduction to produce a unique individual half the genes come from each parent.

11. Be able to explain why sperm cells are produced in large numbers to increase the chance of fertilisation.

12. Be able to explain the advantages of being multicellular:

    • a) allows organism to be larger

    • b) allows for cell differentiation

    • c) allows organism to be more complex.

13. HT only: Be able to explain why becoming multicellular requires the development of specialised organ systems, limited to:

    • a) communication between cells

    • b) supplying the cells with nutrients

    • c) controlling exchanges with the environment.

14. Know that new cells for growth are produced by mitosis.

15. Be able to explain why these new cells are genetically identical.

16. Know that in mammals, body cells are diploid (two copies of each chromosome).

17. Be able to explain why DNA replication must take place before cells divide.

18. HT only: Be able to describe how, prior to mitosis, DNA replication occurs, to include:

    • a) ‘unzipping’ to form single strands

    • b) new double strands forming by complementary base pairing.

19. HT only: Be able to describe how in mitosis the chromosomes:

    • a) line up along the centre of the cell

    • b) they then divide

    • c) the copies move to opposite poles of the cell.

20. Know that gametes are produced by meiosis.

21. Be able to describe gametes as haploid (contain one chromosome from each pair).

22. Be able to explain why fertilisation results in genetic variation, limited to:

    • a) gametes combine to form a diploid zygote

    • b) genes on the chromosomes combine to control the characteristics of the zygote.

23. Be able to explain how the structure of a sperm cell is adapted to its function, to include:

    • a) many mitochondria to provide energy

    • b) an acrosome that releases enzymes to digest the egg membrane.

24. HT only: Be able to explain why, in meiosis, the chromosome number is halved and each cell is genetically different, to include

    • a) one chromosome from each pair separate to opposite poles of the cell in the first division

    • b) chromosomes divide and the copies move to opposite poles of the cell in the second division.