Mitosis In Onion Root Tip Cells Lab 271x5n

Name: _______________________ Class: __________________ Date: _________________

Mitosis in Onion Root Tip Cells Introduction Mitosis is the process by which the cell nucleus is divided into two nuclei. Mitosis takes place in four phases: prophase, metaphase, anaphase, and telophase. The period between one mitosis and the next is called interphase. Chromosome replication occurs during interphase. Organisms such as the common intestinal bacteria E. coli can complete mitosis in 30 minutes. Other cells require days. In some cells, such as human muscle cells, mitosis never occurs. In this investigation, you will determine the time required for plant cells to go through each phase of mitosis.

Problem How can the time needed for each phase of mitosis be determined in a plant cell?

Materials Textbook (or mitosis notes handout) Prepared slide of plant mitosis (onion root tip) Microscope Calculator

Safety Handle all glassware carefully. Always handle the microscope with extreme care. You are responsible for its proper care and use. Use caution when handling glass slides as they can break easily and cut you.

Practice 1. Take a prepared onion root-tip slide. 2. Focus the slide under high (40X) power. Find a cell in interphase and each of the stages of mitosis. Draw one cell to represent each stage below.

Interphase

Biology Teaching Resources

Prophase

http://www.aurumscience.com

Metaphase

Page 1

Anaphase

Telophase

Procedure 3. Review the phases of mitosis by studying that section of your notes. 4. Place the prepared onion root tip slide on the stage of the microscope. Using the low-power objective, focus on the cells just above the tip of the root. Switch to high power and count the total number of cells in the field of view. 5. Without changing the field of view, count the number of cells in each stage of mitosis: prophase, metaphase, anaphase, and telophase. Also record the number of cells in interphase. 6. To determine the approximate proportion of time a cell spends in each phase of mitosis, use the following formula: Hours spent in stage = 24 x Number of Cells in Stage Total Number of Cells Counted

Data Phase of Mitosis

Number of Cells in Phase

Class Total Number of Cells in Phase

Calculated Duration (hours) (24 x number of cells in stage / total cells in view)

Interphase Prophase Metaphase Anaphase Telophase

Page 2

Graph 1: Bar graph of the number of cells in each phase of mitosis (class data)

Graph 2: Pie chart of the hours of the day spent in each phase of mitosis (out of 24 hours)

Analysis 1. In which phase of mitosis is the most time spent? The least? 2. Based on your results, about what percent of a cell’s life is spent in interphase versus mitosis? 3. Interphase is sometimes called the “resting stage”. Explain why this is inaccurate.

4. What form does DNA take during interphase? What does it look like?

5. What form does DNA take during mitosis? What does it look like?

Page 3