Onion Root Tip: Phases of the Cell Cycle

Objective: To determine the percent of time a cell spends in the different cell cycle phases.

Procedure:

  1. Go to “biology.arizona.edu”
  2. Click on the Biology Project
  3. Click on Cell Biology
  4. Click on Activities
  5. Click on Online Onion Root Tip: phases of the cell cycle
  6. Follow the directions

Pre-lab Questions:

  1. How do you recognize a cell in interphase?
  1. How do you recognize a cell in prophase? What is the function of the kinetochores?
  1. How do you recognize a cell in telophase? What is cytokinesis?
  1. Why are we examining cells from the root tip of the onion?
  1. How are the cells that you are using in this experiment prepared?
  1. Study the mitosis animation. What do the authors mean when they say the cell cycle is a continuous process?

Data Table 1: Cells in Each Cell Cycle Phase

Interphase / Prophase / Metaphase / Anaphase / Telophase / Total
# of Cells / 36
Percent / 100%
Time required (minutes) / 720

Analysis:

Determine the total time required for each phase of mitosis by using your data and the formula below.

Time for phase = # of cells in phase x 720 minutes

total # of cells counted

Using the data from the table you just made, prepare a circle graph which shows the number of minutes that onion cells spend in each phase of mitosis. The following suggestions may aid you in preparing your graph.

  1. The entire circle is 720 minutes. So, if a phase takes 360 minutes

it would take up exactly half of the graph.

  1. You can approximate the time.
  2. Shade each phase on the graph with a different colored pencil.
  3. Make a key to match your graph.

Figure 1: Circle Graph of Time Spent in Each Phase

Analysis Questions:

  1. What is the first stage of mitosis when the chromosomes become visible?
  2. During metaphase where are the chromosomes located? Where are they during anaphase?
  3. During what stage does the nucleus reappear?
  4. During what stage can you begin to see the cell plate forming?
  5. Which phase requires the longest time for completion?
  6. Which phase requires the shortest time for completion?

Results:

State each phase of the cell cycle and the percent of time spent in each phase.

Conclusion:

( Do not use the first person in your conclusion. Use the third person.)

Discuss what happens in interphase and each phase of mitosis.

Discuss why a cell would spend the most amount of time in the phase you determined to be the longest.