1. 1 CELL CONTINUITY

2. 2 Contents Cell continuity Chromosome Sexual reproduction Mitosis Meiosis Cell division – Mitosis Cancer

3. 3 Cell Continuity Is the ability of cells to divide and survive from one generation to the next. It involves growth, synthesis and reproduction. It can be summarised in the “cell cycle”.

4. 4 Cell Cycle – flow chart

5. 5 Chromosome rod like structure composed of DNA and proteins, contains the genetic information (genes) which is passed from one generation of cells or organisms to the next – occur in pairs in most plant and animal cell nucleii.

6. 6 Chromosome Structure

7. 7 How many chromosomes? Each species has a characteristic number of chromosomes. In humans this is 46 i.e. two sets of 23, you get one set from each parent. As a result you have two of each type of chromosome. This is called the diploid number (2n).

8. 8 Sexual reproduction (1/2) Two sex cells fuse to form a new organism. If two diploid cells were to fuse, what would happen to the number of chromosomes in the next generation? It would double. And in the next generation what would happen? Double again.

9. 9 Sexual reproduction (2/2) If this continued to happen eventually the cell would be filled by a nucleus. To prevent this happening, special cells are produced which contain only half of the diploid number of chromosomes. These cells are called gametes and are haploid (n) i.e. they contain only one set of chromosomes.

10. 10 Cell Division There are two types of cell division: - Mitosis Mitosis, and Meiosis

11. 11 Mitosis Is a type of cell division that produces cells which are identical to the original parent cell 1 n cell  mitosis  2 x n cells 1 2n cell  mitosis  2 x 2n cells

12. 12 The Products of Mitosis

13. 13 Function of Mitosis In single celled organisms, e.g. amoeba, bacteria, etc., mitosis allows the organism to multiply. In multicellular organisms, e.g. most plants and animals (including humans), mitosis is primarily for growth. Back to Types of Cell Division

14. 14 L.S. Root tip - Onion - mitosis.

15. 15 Meiosis (1/3) Is a type of cell division that produces cells which have only half of the genetic information of the parent cell i.e. 1 2n cell  meiosis  4 x n cells One diploid (2n) cell divides to produce four new dissimilar haploid (n) cells.

16. 16 Meiosis (2/3) Each haploid cell is given one chromosome from each chromosome pair of the original cell. See Products of Meiosis See Products of Meiosis Chromosomes are passed to the haploid cells (gametes or spores) independently of each other. Large numbers of different haploid cells can be produced.

17. 17 Meiosis (3/3) e.g. in the human there are 23 pairs of chromosomes  2 23 possible gametes – for both sperm and egg production  (2 23 ) 2 different fertilisation combinations = 8,388,608 = 70,368,744,177,664

18. 18 The Products of Meiosis Back to Slide 14

19. 19 Functions of Meiosis To produce haploid cells – all of which are different To produce a variety of gametes, as a result of independent assortment The variety of gametes leads to variation from generation to generation by re- arrangement of chromosomes and genes Variations are the functional units of evolution

20. 20 Products of Mitosis & Meiosis compared MitosisMeiosis

21. 21 Cell Division – Mitosis The process of mitosis occurs in four stages: - Prophase Metaphase Anaphase Telophase But between telophase and prophase there is a preparation stage: - Interphase Go here first

22. 22 Interphase Resting / preparatory stage between divisions. Cells build up a supply of energy to complete the division process. Chromosomes replicate (duplicate). Organelles duplicated Back to the Four Stages

23. 23 Mitosis Summary

24. 24 Prophase Chromosomes thicken and become apparent - chromosomes have duplicated. Each pair of sister chromosomes held by centromere. Nucleolus disappears. Centrioles separate and migrate to opposite ends of cell - form ‘poles’. Spindle fibres form from pole to pole. Nuclear membrane disappears.

25. 25 L.S. Root tip - Onion - mitosis. prophase & interphase.

26. 26 Diagram of Prophase Back to the Four Stages Sister Chromosomes Nuclear membrane

27. 27 Metaphase Spindle fully formed. Chromosome pairs attached to spindle by centromere - arrange along 'equator'.

28. 28 L.S. Root tip - Onion - mitosis. metaphase

29. 29 Diagram of Metaphase Back to the Four Stages Sister Chromosomes

30. 30 Anaphase Centromeres split. Chromosomes separated and pulled towards opposite 'poles'

31. 31 L.S. Root tip - Onion - mitosis. anaphase

32. 32 Diagram of Anaphase Back to the Four Stages

33. 33 Telophase Nuclear membrane forms around two new nuclei - chromosomes begin to disappear Cell membrane constricts between both nuclei – cleavage furrow forms in animal cells and cell plate forms in plant cells. Each new daughter cell now contains the same number of chromosomes as the parent cell.

34. 34 L.S. Root tip - Onion - mitosis. telophase

35. 35 Diag. of Telophase – Animal Sister Chromosomes

36. 36 Telophase – Plant Cell Cell wall formation

37. 37 Mitosis Vs Meiosis (1/2) Can take place in haploid or diploid cells. Daughter cells have same no. of chromosomes as parent. Produces two daughter cells identical genetically Can take place in diploid cells only. Daughter cells have half the no. of chromosomes as parent. Produces 4 daughter cells - may all be different genetically.

38. 38 Mitosis Vs Meiosis (2/2) Occurs in somatic cells. One division (anaphase) Occurs in gamete or spore producing cells only. Two divisions.

39. 39 Cancer Cancer is the uncontrolled growth of cells. In all cases the control of cell division is lost. Cells divide more rapidly than usual and produce a large mass of cells called a tumour. Some parts of this tumour may then spread to other parts of the body.

40. 40 The effects of a cancerous cell

41. 41 Cause of Cancer Cancer is caused by a change (mutation) in the parts of the DNA of a cell that controls cell division. These parts are called the oncogenes, and when sufficient of these are damaged control of cell division is lost. Environmental factors that cause DNA mutations are called carcinogens.

42. 42 Carcinogens Risk of cancer increases with age – mutations build up over time Chemicals e.g. smoking Radiation e.g. from the sun, x-rays Diet – moderate intake of all food types Some people may inherit an increased likelihood of getting a certain small number of cancers

43. 43 END