Lab 9 – Mitosis
Objectives
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Identify the stages of mitosis in whitefish blastula and onion root
Calculate which cell cycle stage cells spend most of their time
Introduction
A cell has a life cycle that is referred to as the cell cycle, which is divided into two major
phases: interphase and cell division phase. When the cell is not dividing, it is in G1 stage of
interphase, participating in its normal duties. When triggered to divide, the cell will replicate its
genetic material (DNA) in the S stage of interphase to guarantee that there’s enough DNA to
pass to newly forming daughter cells. After making more proteins in G2 stage of interphase, the
cell is ready to divide.
Cell division involves both nuclear division (dividing the DNA) and cytoplasmic division
(cytokinesis). There are two types of nuclear division: mitosis and meiosis. This lab will focus
on mitosis. During mitosis, DNA is very precisely divided to ensure that each daughter cell has
the same genetic material and capabilities of the parent cell from which it arose. For instance, if
an epithelial cell divides, the two newly formed epithelial cells are identical to each other and
identical to the original dividing parent cell in DNA information. Mitosis occurs in cells
throughout your body.
Cytoplasmic division (cytokinesis) occurs so that two new cells form from one original
dividing parent cell. In animals, the plasma membrane of the dividing parent cell pinches in and
separates the two newly formed daughter cells. The pinched membrane is called a cleavage
furrow. In plants, a collection of vesicles called a cell plate separates the two newly formed
daughter cells. Nuclear division can take place without cytoplasmic division. In a flowering
plant’s embryo sac, a central cell has two nuclei. This is possible because nuclear division
occurred but cytokinesis did not.
Some cells divide by mitosis and cytokinesis at an incredibly rapid pace (such as those on
your palms), while others (such as nerve cells) do not reproduce at all in the mature adult. In
some cases, mitosis and cytokinesis are ways to replace damaged or aging cells and to repair
damaged tissue. Cell division is also crucial to increase the number of cells as we grow from
baby to adult.
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Lab 9 – Mitosis
9.1 Plant mitosis
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7.
Obtain a microscope, one hand on base and one hand on arm.
Select an Allium (onion) root mitosis slide.
Using proper microscope procedures, observe the cells under scanning power objective,
then under low power objective (fine focus only), and then under high power objective
(fine focus only).
Choose the area of the root near the tip. This area contains many cells that are dividing.
Choose one representative cell in interphase. Draw this cell and answer questions on
QUESTIONS page.
Choose one representative cell in each stage of mitosis (prophase, metaphase, anaphase,
telophase). Draw each stage in the appropriate places and answer questions. If you are
not able to find a cell in a particular stage, move to a different root.
After you have identified all the stages, focus in on one root, at an area near the tip with
lots of cells dividing.
a. Count the total number of cells.
b. Count the number of cells in interphase.
c. Count the number of cells in prophase.
d. Count the number of cells in metaphase.
e. Count the number of cells in anaphase.
f. Count the number of cells in telophase.
9.2 Animal mitosis
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Select a whitefish blastula mitosis slide.
Using proper microscope procedures, observe the cells under scanning power objective,
then under low power objective (fine focus only), and then under high power objective
(fine focus only).
Choose one representative cell in interphase. Draw this cell.
Choose one representative cell in each stage of mitosis (prophase, metaphase, anaphase,
telophase). Draw each stage in the appropriate places.
9.3 Completing Microscope Checklist
1.
Before leaving, complete the Microscope Checklist to prepare the scope for the next lab.
Also, ask the instructor to initial your checklist and look at your scope before you put the
scope away.
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Lab 9 – Mitosis
9.1 QUESTIONS
Draw one cell per phase for Allium:
Interphase
Prophase
1.
Look at the cell in interphase. Is there a nuclear membrane present? Therefore, is an Allium
cell a eukaryotic cell or a prokaryotic cell?
2.
Look at the cell in prophase. Describe what is happening to the nuclear membrane in
prophase.
3.
Describe the difference you see between chromatin in interphase and the chromosomes in
prophase.
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Lab 9 – Mitosis
Metaphase
Anaphase
4.
Look at the cell in metaphase. Where are the chromosomes in the cell?
5.
Look at the cell in anaphase. What is happening to the sister chromatids?
Telophase
6.
Look at the cell in telophase. Compare the length of a cell in telophase with the length of a
cell in prophase or metaphase.
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Lab 9 – Mitosis
7.
Select one field of view. Fill in the following table with the number of cells in each phase:
Phase
# cells
Interphase
Prophase
Metaphase
Anaphase
Telophase
Total
Based on the above table, cells spend the majority of their time in which phase?
8.
Mitosis and cytokinesis occur so that one cell divides to form two identical cells with
identical genetic information. Give one example of a situation why mitosis and cytokinesis
would be important for you.
9.
Mitosis means to divide the DNA equally. Cytokinesis means to divide the cytoplasm (the
rest of the cell).
a. In plant cells, what structure is visible between newly forming cells to indicate that
cytokinesis is occurring?
b. In animal cells, what structure is visible between newly forming cells to indicate that
cytokinesis is occurring?
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Lab 9 – Mitosis
9.2 QUESTIONS
Draw one cell per phase for the whitefish blastula:
Interphase
Prophase
Metaphase
Anaphase
Telophase
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