1. The Cell Cycle

2. Why do cells divide?
For growth, repair, and reproduction

3. When do cells divide?
Most limiting factor in size is the size of the cell membrane.
A cell has to stay small so that all the things that need to go in and out don’t have too far to travel. The surface area to volume ratio must be small so cells stay tiny and divide instead of growing too big.

4. How Do Cells Divide?
Cell cycle - sequence of phases in the life cycle of the cell

7. Interphase 3 parts: G1, S and G2 G1 - cell growth; make new organelles
S – DNA replication
G2 – short; organelles for cell division are produced

8. Mitosis

9. What is Mitosis?
The process whereby body cells (somatic) are made by cell division
Asexual

10. How does it work?
4 Stages

11. 1st - Prophase Chromosomes become visible
Centrioles go to opposite sides
Spindle fibers form
Nuclear membrane breaks down

12. -2- Metaphase- Chromosomes line up along the equator in pairs
-3- Anaphase- Chromosomes move to opposite ends of the cell
-4- Telophase- a cleavage furrow forms and…
each cell now has exactly the same number of chromosomes!

13. Cytokinesis
Cytoplasm pinches in half

14. Mitosis
Results in an exact duplicate of the same cell. There is no change.

17. Interphase

18. Prophase

19. Metaphase

20. Anaphase

21. Telophase

25. MEIOSIS
Chapter 11

26. So, What is Meiosis?
The process whereby gametes or, sex cells are made by cell division
Examples are sperm & eggs only!

27. How does it work? Prophase II Metaphase II Anaphase II Telophase II
8 Stages
Prophase I (includes chromosomes crossing over and exchange)
Metaphase I
Anaphase I
Telophase I
Prophase II
Metaphase II
Anaphase II
Telophase II

28. The same things occur with chromosomes except the number of chromosomes is halved

29. Meiosis results in cells that have only 23 chromosomes in humans
Men make 4 sperm cells
Women make 1 egg and 3 polar bodies (which are excreted as waste products

30. Why is meiosis so important?
It provides for genetic variation
crossing over occurs in prophase I and II
shuffling of chromosomes (or genetic information)

32. Mitosis Meiosis Body cells/ somatic cells 4 Stages 1 division
Results in 2 daughter cells
Asexual
Growth
2n - diploid
Sex cells / gametes
8 stages
2 divisions
Results in 4 sperm or 1 egg & 3 polar bodies
Sexual reproduction
Crossing over – prophase I
1n - haploid