Biology 100 CellLaboratory

Cell Cycle Stage Duration Comparisons

Cell Cycle and Mitosis

For cells that divide by mitosis there are three major parts of the cell cycle:  interphase, mitosis, and cytokinesis.  Review these major parts and answer the following questions so you are familiar with the major stages before beginning the laboratory.

1. DNA is replicated during ______________________________.
2. A normal cell spends most of its time in ____________________________.
3. During ________________________ a muscle cell would be producing the proteins required to function as a muscle cell, such as proteins involved in muscle contraction.

4. Duplicate chromosomes move to opposite poles of a cell during _______________.
5. __________________ is complete when the genetically identical daughter cells are two distinct cells

Background

Multicellular organisms grow by making more cells.  A cell undergoing its cell cycle and mitosis results in two identical daughter cells.  In plants special growth areas called meristems are typically found at the tips of roots and stems.  In animals, growth is usually not relegated to a specific area of the organism.

For this lab we will be using prepared onion root tip slides to study plant mitosis and calculate the relative duration of the stages of mitosis.  The cell cycle for actively dividing onion root tips is approximately 24 hours.  Since these cells are not living, we will estimate the time each cell spends in each stage based on what percentage of the cells are in each phase.

Mitosis is divided into the following stages: prophase, metaphase, anaphase, and telophase.  Match each stage with the major action taking place in the cell and then review the photos of onion root cells in Interphase and different stages of mitosis.

Match by drawing a line from the stage to the correct description of the cell activity:

Credit: © Carolina Biological/Visuals Unlimited

Onion root tip mitosis – Interphase stage.

Credit: © Carolina Biological/Visuals Unlimited Onion root tip mitosis – Metaphase stage.

Credit: © Carolina Biological/Visuals Unlimited Onion root tip mitosis – Early anaphase stage.

Credit: © Carolina Biological/Visuals Unlimited Onion root tip mitosis – Late anaphase stage.

Credit: © Carolina Biological/Visuals Unlimited Onion root tip mitosis – Telophase stage.

Major Question

Does a cell spend equal amounts of time in each of the stages of the cell cycle?

Develop Hypotheses

Remember, a hypothesis is a tentative and testable explanation for an observation or answer to a question.  In the space below describe your hypothesis or hypotheses and the reasoning behind why you expect that cells will or will not spend equal amounts of time in each of the major stages of the cell cycle (interphase, prophase, metaphase, anaphase, and telophase).

Setting up your experiment and lab report

Your lab report for the Cell Cycle Lab should include the following headings:

1. Introduction-Compose a short introduction describing the typical cell cycle. Then include the answers to the fill-in and matching questions above.
2. Question-copy and paste the “Major Question” given above.
3. Hypothesis-complete the section above entitled “Developing Hypotheses”.
4. Procedure-copy and paste the “Procedure”given below.
5. Results and Discussion-For convenience the results and discussion are combined in this lab. Be sure to enter the data in the data table below and include the table in this lab report section.Then answer the five questions given below in the section entitled “Results and Discussion”.
6. Submit the completed Cell Cycle Laboratory Report in the Cell Cycle Lab Drop Box in the Cell Cycle Lab module.

Materials List

Images from prepared mitosis microscope slides

Procedure

1. Use the images posted in the cell cycle module in Canvas to study individual cells. There are three images to represent three different fields of view.
2. For each cell in each field of view, determine which stage of mitosis the cell is in.
3. Count all cells in each stage of the cell cycle in all three fields of view.
4. All data should be recorded in the data table below.
5. Use the formulas below to calculate percent of total cells counted in each phase as well as time in minutes for each stage.

Data Table

To determine the percent of total cells counted for each stage use the following formula:

(Total cells counted in each stage / Total cell counted) X 100

For example: if a total of 5 cells were counted in telophase and the total of all cells counted was 322, then the percent of total cells counted in telophase would be 5/322 = 0.015 X 100 = 1.5% To determine the minutes of the cell cycle spent in each stage use the following formula:

Percentage of cells in stage X 1,440 minutes For example: 1.5% X 1440 = 21.6 minutes

Results and Discussion

1. What is most common stage of the cell cycle (other than interphase)?

2. What is the next most common stage?            

3. Which stages do you not often see?

4. What does this tell us about the time for different stages of mitosis versus the rest of the cell cycle?

5. Relate these results to your hypothesis/hypotheses. Were your ideas supported by the data?  How confident are you in your conclusions?