Cell Division: Mitosis and Meiosis

Georgia Perimeter College

Objectives

  1. At the conclusion of this exercise, students will know understand mitosis.
  2. Students will understand what happens to the DNA and chromosomes in a cell during each of the 4 phases of mitosis.
  3. At the conclusion of this exercise, students will understand the difference between mitosis and meiosis.
  4. Students will understand the term homologous chromosomes.
  5. Students will understand the significance of the ďcrossing-overĒ process in the prophase 1 of meiosis.
  6. Students will understand why meiosis can occur only in sex cells.
  7. Students will understand why the chromosome numbers always remain the same even after fertilization.

Chromosomes / Cell Mitosis

In order for growth to occur, the cells must divide. One cell divides into two, the two divides into four and the four divides into 8 and so on.

Q. How do cells divide?

Activity: Cell division

Introduction

In preparation for cell division, the thread-like DNA coils and thickens to form what is called a chromosome.

Each living thing has a precise number of chromosomes in the cell.

Just prior to cell division, the chromosomes line up in the center of the cell. Other cell organelles, the two centrioles, produce spindles (thread-like in appearance). Some of these spindles attach themselves to the central part on each chromosome. These spindles later start to retract in opposite directions, causing the chromosomes to split into two equal halves.

Each chromosome now becomes two half chromosomes called chromatids. These chromatids migrate to opposite poles of the cell with the help of the spindles. The cell fluid and all the other things inside each cell separate along with these chromatids as they pool to opposite poles (or ends) of the cell.

The cell ultimately divides into two, each cell carrying a half sister chromosome of the other, a process called mitosis.

Materials

  • An online video of mitosis
  • Paper and Pencils for drawing of chromosomes inside a cell
  • Drawings of cells to illustrate the formation of spindles and the separation of chromatids to opposite poles of the cell, using a mitosis model and a diagram as a guide.
  • Mitosis models to show the 4 phases of mitosis
  • Magnetic models of chromatids and chromosomes to illustrate the separation of chromatids during anaphase and during the division of the cells.
  • Slides of onion root tips showing mitosis
  • Slides of animal cells showing mitosis

Procedure

  • Students will watch a video of mitosis.

  • Students will observe demos of slides set-up to show cell division in animals and in plants.

  • Students will use models to study the 4 phases of cell division.

  • Students will draw cells to show the phases of cell division.

  • Studentsí drawings will show how one cell can ultimately become a multicellular tissue.

 

Activity: Onion Root Tip Experiment - part 1

Background information

  1. Learn about cell division by working through the interactive tutorial on mitosis.
  2. Learn about cell division in onion root tips.
    Online onion root tips - p. 1
    Online onion root tips - p. 2 description
    Online onion root tips - p. 3 determining time spent in different phases of the cell cycle.
  3. Watch a YouTube video of mitosis.

Materials

  • Onion

  • Container of water

  • Microscope slides

  • Toluidine blue

  • Compound microscope

  • Paper towel

Procedure

1. Set the bottom part of an onion in water.  Leave it there for about 4-5 days, until the roots begin to grow.
2.  When the roots are about 2 cm long, with active growth, cut several millimeters of some of the the roots off.
3.  Place the roots on a microscope slide, cut them lengthwise.
4.  Press another slide down on the roots to mash them, and then remove the top slide.
5.  Add some nuclear stain such as toluidine blue.
6.  To stop the cell division and to quicken the stain, warm the slide over a flame for a few seconds, without allowing the liquid to boil.
7.  Add a few more drops of stain and let the sample sit for a few minutes.
8.  After a few minutes, blot the stain with a paper towel.
9.  Add a few drops of water, and put a coverslip on it.
10.  Observe with a microscope.  Look for the various stages of cell division.

 

 

Activity:  Onion Root Tip Experiment - part 2 - Flashcards

Materials

Ward's Mitotic Stage Flashcards

Procedure

Each student is given several flash cards.  Identify the stage of mitosis of each cell, and make a count of the number of cells in each stage.  Compile your data in the table below.

From this, determine the percentage of cells in each stage of cell division.  The more cells in any particular stage of cell division, the longer the relative duration of that particular stage. 

List the stages in order of their relative duration, ranging from the longest duration to the shortest duration.

  Interphase Prophase Metaphase Anaphase Telophase Total
number of cells  
percent of cells 100%

 

Longest duration

 

 

Shortest duration


 

Meiosis

Why do children resemble their parents?

This is explained in a process known as inheritance. It explains how we can obtain traits from our parents and pass them on to our children.

This process involves a cell division called meiosis, which is slightly different from mitosis. When meiosis is ready to start; similar chromosomes (called homologous) that were inherited from each of the two parents line up in pairs inside the cell. (Remember that chromosomes are made up of coiled DNA; each unit of DNA is a gene / trait). These chromosome pairs exchange some of their genes through a process called crossing-over. At the end of crossing-over the chromosomes pairs are now different from the original chromosomes that were there at the beginning of meiosis. These pairs of chromosomes are later separated from each other with the help of the spindles (as in mitosis) and migrate to opposite poles of the cell. Immediately division of the cell into two daughter cells occurs. Each daughter cell now carries half the number of the chromosomes of the original the cell. This is how the sperm and egg cells are produced. Each manís sperm carries the chromosomes with traits of both manís parents similarly each womanís egg carries chromosomes of the womanís parents.  Sperm and egg cells always have half the number of chromosomes when compared to other cells.  When these two cells (egg and sperm) unite again during fertilization, the full number of chromosomes of a cell is restored in the cell. The children who are the product of this union have cells that carry traits of parents and grand parents from both sides of the families.

Activity

Materials

  • Video to show animation of meiosis

  • Magnetic models of chromosomes to illustrate crossing over.

  • Models to show illustrations of meiosis

  • Paper and colored pencils

  • Drawing of cells using different colors to show similar (or homologous) chromosomes.

Procedure

  • Students will watch a video of meiosis.
  • Use the meiosis model to study the different phases of meiosis.
  • Use the magnetic chromosome models to illustrate formation of tetrads / synapsis and crossing-over in the cell; students can also use the magnetic chromosomes to illustrate the appearance and arrangements of chromosomes at the 4 phases of the meiosis.
  • Draw diagrams of homologous chromosomes in the cell using coloring pencils to show fatherís chromosomes and motherís chromosomes in each cell.
  • Use coloring pencils to draw diagrams that illustrate the crossing over stage, metaphase, anaphase and telophase in cycle one of meiosis.

 

 

 

 

 

Activity suitable for elementary students

A. DNA structure

Objectives

At the conclusion of this exercise activity, students will be able to describe the alpha helical structure of a eukaryotic cell DNA found in the nucleus of a cell.

Materials
Paper
Colored Pencils
Petri dish covers (6 inches and 3 inches in diameter) to be used to draw circles
DNA models to show the 4 nucleotides and the alpha helical structure.

Procedure

  • Students will draw circles to represent cells using the 6 inches diameter Petri dishes; using the 3 inches diameter Petri dishes they draw a second circle inside the first one.
  • Students will draw a double spiral thread-like structure inside the second circle to represent DNA strands inside a nucleus.
  • Students will study a plastic model of the DNA structure and the nucleotides pairing.

 

 


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Content provided by Patricia Ahanotu, Catherine Carter, Essie Smith, and Pamela Gore, Georgia Perimeter College

Page created by Pamela J.W. Gore
Georgia Perimeter College,
Clarkston, GA

Page created August 9, 2007