1. February 23, 2012 What do you know about the cell cycle?
Is there a limit to how big a cell can grow?
What’s one reason why a cell might need to replicate?

2. Chapter 9 Cellular Reproduction

3. Cell Size Limitations Why are cells so small?
Key factor is surface area to volume ratio
Surface area in the cell is the area covered by the plasma membrane.
The volume refers to the space taken by the inner contents.

4. Cell Size Limitations
The smaller the cell, the higher ratio of surface area to volume
This allows cells to sustain themselves more efficiently.

5. Cell size limitations
As a cell grows, the volume increases while the surface area decreases.
Why could this be bad for the cell?
Makes diffusion of substances slow and difficult
Makes it difficult for cells to communicate instructions.

6. So, what happens when the cell reaches its size limit?

7. The Cell Cycle
When a cell reaches its size limit it will either stop growing or divide—most will divide.
Red and white blood cells, nerve cells, heart muscle, and skeletal muscle cells do not divide.
Eukaryotic cells reproduce by a cycle of growing and dividing called the cell cycle.
Prokaryotic cells reproduce by binary fission.

8. The Cell Cycle Interphase Mitosis Cytokinesis
Longest part of the cell cycle
Occurs in three stages: G1, S, G2
Mitosis
Division of cell nucleus
Occurs in four stages: Prophase, Metaphase, Anaphase, Telophase
Cytokinesis
Division of the cytoplasm which results in two new cells

10. Interphase G1 phase (Gap 1) S phase (Synthesis) G2 phase (Gap 2)
The cell is growing and carrying out normal cell functions
S phase (Synthesis)
DNA replication
G2 phase (Gap 2)
Replication of organelles
Cell prepares for mitosis

12. How long does the entire cell cycle take to complete?

13. Duration of cell cycle Varies depending on the type of cell
Some divide in as little as eight minutes while others might take up to one year.
For most normal animal cells, the cycle takes hours to complete
Some cells do not divide at all—they stay in G1 phase

14. February 24, 2012 What is the longest part of the cell cycle?
What are the three stages of interphase?
How long does the cell cycle take to complete in a normal, actively dividing animal cell?

15. What’s the difference?
Chromatin: relaxed form of DNA in the cell’s nucleus
Chromosome: Looks like an “X” in mitosis; condensed chromatin
Chromatid: half of the “X” shaped chromosome

17. Prophase Longest phase of mitosis
Chromatin condenses into visible chromosomes
Nuclear membrane dissolves/nucleolus disappears
Spindle apparatus begins to form

18. Metaphase
Chromosomes attach to spindle apparatus and align in the middle of the cell.

19. Anaphase
Chromosomes separate and move to opposite poles of the cell.

20. Telophase Chromosomes decondense into chromatin.
Nuclear envelope/nucleolus reforms

21. Cytokinesis
Animal cells: cleavage furrow forms and pinches inward until the cell divides in two
Plant cells: Cell plate forms dividing daughter cells

23. February 27, 2012 What is the longest phase of mitosis?
Explain the difference between a chromosome and a chromatid.
Compare and contrast cytokinesis in plant and animal cells.