Mitosis / Meiosis Web Assignment NAME:

ONION ROOT TIPS AND THE CELL CYCLE

Actively dividing cells pass through a predictable series of stages called the cell cycle. A cell cycle starts with interphase, just after a new cell is formed by mitosis. During interphase, the cell duplicates its DNA and increases its mass and number of cytoplasmic components. This prepares the cell for the next round of mitosis. The cell cycle ends when the cell divides. If you look under a microscope at cells from actively dividing tissue, you will find that their cell cycles are not synchronized. Some cells are in interphase, while others are in the various stages of mitosis. By noting the number of cells in each stage, it is possible to calculate the relative lengths of each phase of the cell cycle.

Activity

In this activity, you will calculate the lengths of the various phases of the cell cycle in an onion root tip. First you will view some slides and graphics of onion root tips provided by the Molecular Expressions Photo Gallery. Then you will complete the online activity provided by the Biology Project at the University of Arizona.

Part 1.

Use your browser to go to Molecular Expressions Photo Gallery: Mitosis

http://www.microscopy.fsu.edu/micro/gallery/mitosis/mitosis.html

Notice in the micrograph at the top of the page that there are cells in a variety of stages. View the onion slides in this section, then click on "mitosis" in the sentence "Learn the steps in mitosis ... " This will take you to a Java tutorial. Keep in mind what you have learned here as you proceed to the second part of the activity.

Part 2.

Use your browser to go to Online Onion Root Tips at

http://www.biology.arizona.edu/cell_bio/activities/cell_cycle/assignment.html.

Begin by reading the description of the five major cell phases. You will need to keep this information in mind during the activity.

Make a copy of the data sheet that appears on the second page. You will need it to answer the questions.

Proceed through the activity, identifying the phase for each cell you are shown. Pay attention to the hints if you misidentify a cell at first.

When you have completed the activity, answer the following questions:

1. What percent of cells were in interphase?

2. What percent were in mitosis?

3. Which phase of mitosis takes the longest?

4. During which stage is the nucleolus visible as a dark spot?

5. How can you recognize a cell in metaphase?

Part 3.

Visit the Interactive Mitosis Meiosis diagram

Go to:

http://w3.dwm.ks.edu.tw/bio/activelearner/09/ch9intro.html

Use the Next button at the top right corner to read the tutorial screens. Then go back and click Tutorial Activity. Complete the Tutorial Activity.