Pre-lab Questions:

1. How did you develop from a single-celled zygote to an organism with trillions of cells? How many mitotic cell divisions would it take for one zygote to grow into an organism with 100 trillion cells?

2. How is cell division important to a single-celled organism?

3. How does the genetic information in one of your body cells compare to that found in other body cells?

4. Why is it important for DNA to be replicated prior to cell division?

5. How do chromosomes move inside a cell during cell division?

6. How is the cell-cycle controlled? What would happen if the control were defective?

Lab Part 1:Figure 6 is a picture of a slide of an onion root tip, or meristem. Practice identifying cells in the various stages of the cell cycle by counting the cells in Figure 6. Complete the table below.

Transfer the information from Table 1 to Table 2 so that we can examine mitosis, excluding the cells in interphase.

Table 2: Count of cells in the various stages of mitosis.

The percentage of cells found in each phase is a measure of how long each phase lasts. For example, if 25% of the cells in mitosis are in prophase, prophase takes 25% of the total time it takes for a cell to undergo mitosis. Mitosis in onion cells takes about 80 minutes. Calculate the actual time for each phase using the percentages you have just determine.

Duration of phase = percentage/100 x 80 minutes

Table 3: Amount of time spent in each phase of mitosis

Lab Part 2:

You will be comparing the number of cells undergoing mitosis in root tips treated with lectin to the number of cells undergoing mitosis in root tips that are not treated with lectin.

Table 1: Onion root tip data: Non-treated root tips

Table 2: Onion root tip data: Lectin-treated root tips

Table 3: Calculation of Chi-Square Values

Table 4: Chi-Square Distribution Table