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Identify The Various Stages Of The Cell Cycle In Onion Root Tip Cells

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In-lab protocol

Prepare the slides as directed by your instructor and view the cells with a microscope. Refer to the Microscope Handling and Storage page for directions on using the microscope. Draw one large cell viewed through the microscope for each slide preparation below.

Answer the questions posed in the beginning of the At Home portion of the lab by categorizing cells in an onion root tip slide according to the phase of the cell cycle they are in and running a chi-square test to analyze the results.

Use the hypotheses found at the beginning of the At Home portion for this lab. It is recommended that you spend some time familiarizing yourself with the root tip slides on the microscope. Here are a few things to consider about while making these decisions:

  1. In order to test your hypotheses, you need to come up with a plan that allows you to collect data (empirical observations) in a controlled setting and leads to a conclusion. This is the basic structure of an experimental design. Create, in detail, an experimental design to test both of your hypotheses. Remember that hypothesis testing relies on random samples, which means no bias and each observation is independent of the other.
  2. Visit the page http://www.biology.arizona.edu/cell_bio/activities/cell_cycle/cell_cycle.html to again become familiar with the appearance of cells in each stage of the cell cycle.
  3. Based on your hypotheses, what are your expected numbers for each category (use your alternative hypotheses to create these numbers? Create a data table to record your results. (*remember your total of all expected values must equal the total of all observed values)
  4. How will you choose which cells to count/categorize? Will you choose a random selection and how? Will you count some of them or all of them, and how? What about the cells along the edges or in the very middle? What about cells for which you can’t determine the cell cycle stage?
  5. How many cells must you observe to ensure that your lowest expected value in any category is at least 5? (Note- this is a requirement for a valid chi-square test)

Record everything in your lab notebook. Share your plan with the instructor before you begin to collect data. Then, use the prepared onion root tip slides to collect your data. You can start by viewing the slides through the microscope, but then take a picture with your cell phone so you have a still image to collect your actual data from. Record everything you do in your lab notebooks. This will be the data for your research paper!

It is expected that you include a graph depicting the relative numbers of cells counted in each stage of the cell cycle (Interphase, Prophase, Metaphase, Anaphase, Telophase/Cytokinesis) as well as a table depicting the Chi-Squared calculations you performed.

5. Microscope drawings:

  1. Using your in-lab microscope pictures of the onion root tip slide, fill in the data table below and record the number of cells in each stage.


Number of cells






  1. Using the data from the table and the steps listed in the reading, calculate a Chi-Squared value and determine if your calculated result is significantly different from the expected result.

Null Hypothesis: Equal numbers of cells in each of the 5 categories

Alternative Hypothesis (expected): Unequal numbers of cells in each of the 5 categories.

  1. Degrees of freedom:
  1. Calculated Chi-Square (do not need to show work):
  1. Critical Chi-Square (from table):

8. Write a sentence reporting these results.

9. Write a conclusion statement interpreting these results.