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Biology--Mr. Nelson
Phases of the Cell Cycle
Introduction:
Scientists assume that when they examine a population of cells, the number of
cells in each phase of the cell cycle will be proportional to the length of time cells spend
in each phase. ( For example, if there were only two phases, and if cells spent 75% of
their time in Phase 1, then a sample of 100 cells would contain about 75 cells in Phase 1,
and about 25 cells in Phase 2).
Following are the results of an examination of 750 yeast cells taken for a culture.
The number of yeast cells in each phase were both counted and recorded.
Procedure:
1. Mr. Nelson will give you a pie chart for the data above.
2. Use the percentages from your graph to complete the “Percent of cycle” portion of
the data chart above.
Analysis Questions:
1. What phase is the longest in this population of yeast cells?
1a. What are some of the events that happen in this phase?
2. Which phase is longer G1 or G2?
2a. What events happen in the G1 phase?
2b. What events happen in the G2 phase?
3. What percentage of the cell cycle is mitosis?
4. Cells have “trigger proteins” which cause the cell to move from the G phases into
mitosis. If a persons skin cells were deficient in trigger proteins, how might that affect
the person’s recovery time after a cut in the skin?
5. What is the G0 phase? (Use your notes).
6. What advantage might staying at the G0 phase have for a cell?