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Biology Lab: AP Investigation #7 - Cell Division

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Lab Exercise

Biology Lab: Examining Cells for Mitosis

Concept: Eukaryotic cells divide during mitosis in multiple steps that can be recognized by the organization of nuclear materials.

Goal: To isolate and observe chromosomes during cell division.

AP Exam preparation -- Doing the AP version of this lab:

Please read through the AP Labortory Manual, Laboratory #7, Cell Division: Mitosis and Meiosis. If you have access to the equipment and materials used in the lab, please perform the lab as indicated in the Manual. Complete the Lab Manual worksheets and submit your data to the Moodle Biology Website for comparison with the work of your fellow students.
If you are unable to obtain all the equipment and materials required by Investigation #7, you may perform the following alternate lab that uses more readily accessible materials to accomplish the same goal. However, since you should be familiar with the AP Lab as designed, please review that investigation in your lab book.

Alternative Experiment Option #1 to AP Investigation #7

Perform Illustrated Guide to Home Biology Experiments, Lab IV-3, Procedure 1. This lab assumes that you have a professionally prepared mitosis slide. If you do not, use the instructions below to make your own mitosis slide.

Alternative Experiment Option #2 to AP Investigation #7

NOTE: A more detailed version of this experiment is described at Caroline Biological Supply's site on Mitosis.


Procedure (slide preparation):

  1. Clean the onion, especially the roots, carefully.
  2. Put the onion in a wet paper towel in a warm, dark place for 24-48 hours.
  3. Choose a short root (2 mm long); the shorter the root, the faster the growth rate and the greater the likelihood of finding a mitotic cell.
  4. Put the tip on a clean glass slide, and stain it with diluted blue stain (one drop stain to 20 drops water).
  5. Blot excess stain, then stain again.
  6. Place a cover slip or second slide over the root tip, and using a pencil eraser (your finger tip will leave oil deposits), push down and squash the root.

Using your self-made slides, perform the following observations. If possible, obtain commercially prepared slides for onion root tips and whitefish blastual, and repeat the same observations.

  1. Using magnifications near 400X, examine the root slide. You should (if you are lucky) be able to find cells in different stages of mitosis, and even identify chromosomes lined up on the equatorial plane or moving toward the poles of the cell.
  2. Make drawings of the cells in division.
  3. Estimate the size of the cell and the chromosomes you observe, based on your calculations of the field of view size.
  4. Count all the cells in prophase, metaphase, anaphase, and telophase in your field of view. Repeat this measurement for at least three fields:
    StateField 1Field 2Field 3Field 4Total

    Based on the proportions of cells in each stage, what can you infer about the relative length of time an onion root tip spends in each state of mitosis?


Your report should contain a description of your procedure and a verbal description of your observations, as well as your data tables, any analysis you performed, and conclusions you draw.