Module 5 Lesson 2 - 4 (Lab)

Lab: Cell Division Exploration 

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Introduction

All cells follow a cycle. The major divisions are interphase, mitosis, and cytokinesis. Interphase is characterized by growth and protein production. About the mid-point of this phase, DNA is duplicated. Mitosis is the organized sequence of events that divides the genetic information of the cell into two identical sets of chromosomes. Cytokinesis is the physical division of the cell.

How many cells in any given population will be in each stage of the cycle at any time?

Purpose

Manipulate the total length of a cell cycle and observe how many cells in a population will be in any given stage of that cycle.

Materials

For this simulation, you need access to the Internet and a word processing program to record your results.

Procedure

1. Open the following link: Cell Division simulation.
   


2. Follow the instructions listed in the Exploration Guide for
• phases of the cell cycle
• the relative duration of the phases


3. As you read and follow the instructions, be sure you can answer the questions listed.

Assessment Questions

Complete the assessment questions, and check your answers in the simulation.

Calculating the Time Spent in Various Stages of Mitosis

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You can estimate the time a certain type of cell spends in various stages of its life cycle by looking at specimens of the tissue, noting the total number of cells in the images, and then counting the cells you see in each stage at that particular moment.  By using the number of cells in each stage as a fraction of the total cells in the specimen and then multiplying this by the total length of the cell's life cycle, you can determine roughly how long that type of cell spends in each stage of mitosis.  For example, consider the three specimens of onion skin cells from the growing area of an onion root.



Example

Onion meristem cells complete a cell cycle in 720 minutes. Calculate the portion of the cycle spent in interphase.



Solution

1. Calculate the total number of cells.
   

   Specimen 1 = 117 cells

   Specimen 2 = 93 cells

   Specimen 3 = 116 cells

   Total = 117 + 93 + 116 = 326 cells




2. Calculate the total number of cells in interphase.

   Interphase = 95 + 75 + 84 = 254 cells




3. Identify the time to complete a cell cycle.

   A cell cycle is from one interphase to the next interphase.

   Cell Cycle = 720 minutes



4. Calculate the time spent in interphase.



«math xmlns=¨http://www.w3.org/1998/Math/MathML¨»«mtext»Time§#160;in§#160;Interphase«/mtext»«mo mathvariant=¨bold¨»§#160;«/mo»«mo»=«/mo»«mfrac»«mrow»«mn»254«/mn»«mo»§#160;«/mo»«mi»cells«/mi»«mo»§#160;«/mo»«mi»in«/mi»«mo»§#160;«/mo»«mi»interphase«/mi»«/mrow»«mrow»«mn»326«/mn»«mo»§#160;«/mo»«mi»cells«/mi»«/mrow»«/mfrac»«mo»§#215;«/mo»«mn»720«/mn»«mo»§#160;«/mo»«mi»minutes«/mi»«mo»§#160;«/mo»«mo»=«/mo»«mo»§#160;«/mo»«mn»560.98«/mn»«mo»§#160;«/mo»«mi»minutes«/mi»«/math»

The portion of the 720 minutes a cell spends in interphase is 561 minutes. This is why so many cells in the specimen are seen to be in this stage.

Practice Questions

1. Calculate the portion of the cell cycle spent in each of the other stages of mitosis in the onion meristem cell.


Answer
prophase = 102
metaphase = 31
anaphase = 7 (6.6)
telophase = 20
2. Why is looking at three samples rather than just one a good idea?


Answer
It provides validity in case of an error in sampling only one.