Mitosis
Lab
Objectives
1.
Prepare a slide of stained chromosomes using the squash technique.
2.
Identify the stages of mitosis from prepared stained slides of onion root tips
seen under the compound microscope.
3.
Identify the structures visible under the compound microscope of cells in
various stages of cell division.
PROCEDURE
Each
human originates with the fertilization of an egg. At this stage of development
the individual consists of a single cell about the size of the period at the end
of this sentence. Division of this cell and many divisions of sequential cells
over a period of several years, may result in the formation of an adult human,
consisting of about 1018 cells. Among these are cells of many kinds,
each having a different structure, function, and life span. This process of
mitosis, cell division, continues as long as the human or parts of his body are
alive.
In
this investigation you will see the cell in the various stages of mitosis. I.
Staining Chromosomes
Procedures:
1.
With forceps, place an onion root tip in the center of a clean slide. Using a
scalpel or razor blade, cut off the terminal cm of the tip of the root. Dispose
of the rest of the root.
2. Cover immediately
with 3 or 4 drops of the 1N HC1. The acid is to act on the root tip for 5
minutes. During this period the slide is to be heated gently. This is done by
placing the slide on the diffused light source for 5 to 7 minutes. The onion
root tip must be covered with the HCl solution during this warming period.
3.
Blot off the acid without touching the root tip and cover the root tip with 2 or
3 drops of the toluidine blue solution. The stain is to set for about 5 minutes
and is to be warmed in the same manner as with the acid solution
4.
Blot off the stain solution carefully. Add 2 drops of fresh stain solution
carefully and add a cover glass.
5.
With the slide flat on the table, place your thumb on the cover glass exactly
above the specimen. Press straight down hard.
6.
Blot the back of the slide and examine on low power. Look for embryonic cells.
They appear square. When you find mitotic figures, switch to high power.
III.
Draw and label cells in interphase ,prophase, metaphase, anaphase, and telophase
stages of mitosis from slides you prepared.
STAGES OF MITOSIS By
definition:
Prophase
begins when chromosomes are visible with the light microscope and continues
until the nuclear membrane is no longer visible.
Metaphase
begins when nuclear membrane is no longer visible. Chromosomes are in mass in
the center of the cell.
Anaphase
begins when the identical chromosomes start moving toward opposite ends
of the cell.
Telophase
begins with the invagination of cell membrane in animal tissue and with
the first visible evidence of a forming cell plate in plant cells.
Interphase
chromosomes not visible with light microscope (not a stage of mitosis).
1.
Describe the prominent cell morphology as seen through the compound microscope
of animal tissue in each of the following phases:
Interphase |
anaphase |
Prophase |
telophase |
Metaphase |
|
2.
Normal cell functions such as protein synthesis and respiration occur during
which phase?
3.
The duplication of DNA and chromatids occurs during which phase?
4.
If a parent cell has 32 chromosomes, then after mitosis daughter cells each have
how many chromosomes?
5.
Contrast the telophase in animal and plant cells.