1. KEY CONCEPT Cells have distinct phases of growth, reproduction, and normal functions.

2. Objectives
Describe the stages of the cell cycle.
Compare rates of division in different cell types.
Identify factors that limit cell size.

3. Vocabulary
Cell Cycle
Pattern growth, DNA replication, and cell division that occurs in a eukaryotic cell.
Mitosis
Process by which a cell divides it nucleus and contents.
Cytokinesis
Process by which the cell cytoplasm divides.

4. The cell cycle has four main stages.
The cell cycle is a regular pattern of growth, DNA replication, and cell division.

5. The main stages of the cell cycle are gap 1, synthesis, gap 2, and mitosis.
Gap 1 (G1): cell growth and normal functions
DNA synthesis (S): copies DNA
Gap 2 (G2): additional growth
Mitosis (M): includes division of the cell nucleus (mitosis) and division of the cell cytoplasm (cytokinesis)
Mitosis occurs only if the cell is large enough and the DNA undamaged.

6. Cells divide at different rates.
The rate of cell division varies with the need for those types of cells.
Some cells are unlikely to divide (G0).

7. Cell size is limited.
Volume increases faster than surface area.

8. Surface area must allow for adequate exchange of materials.
Cell growth is coordinated with division.
Cells that must be large have unique shapes.

9. Question/Answer
What are the four main stages of the cell cycle?
Gap 1, synthesis, Gap 2, mitosis
What can you infer about the relative amount of time a cell spends in each stage?
An actively dividing cell spends the least amount of time in the mitosis stage. The length of Gap 1 varies the most and is usually the longest.
Do you think a skin cell would have a long or short G1 stage? Explain why.
A skin cell would probably have a short G1. Skin cells undergo a lot of wear and tear because they are exposed on the outside of the body. Therefore, they are probably replaced quickly.

10. Question/Answer
Which has the larger ratio of surface area to volume, a tennis ball or a soccer ball? Explain your reasoning.
A tennis ball, because volume increases more rapidly than does surface area as a ball gets larger.