Download Observing Cell Division

Name: ___________________________
Date: ___________________________
Observing Cell Division
INTRODUCTION
A single fertilized human egg cell will divide to form two cells. These two cells will each divide into two
cells. In time, millions of cells are produced. The division of nuclear material in which each new nucleus
obtains the same number of chromosomes and the same nuclear code as the original nucleus is called
mitosis. Mitosis occurs in four phases. Following mitosis, the cytoplasm divides through a process called
cytokinesis
In this investigation, you will
(a) locate cells in prepared onion root slides that are in the process of dividing by mitosis.
(b) identify cells in interphase and in each of the four stages of mitosis in the onion root tips by
comparing them with diagrams.
(c) study the changes which occur in a cell as it undergoes mitosis.
MATERIALS
• Microscope
• Prepared slides of onion root tip (Allium), longitudinal section
PROCEDURE
• Locate with a microscope the region of rapidly dividing cells on the
prepared slide of onion root tip as shown in Figure 1. After locating
the cells under low power (40×), switch to high power (400×).
• Using the brief descriptions provided below, locate the cells that
appear to be in the various stages of mitosis. Use Figure 2 as a guide.
•
•
•
Using the high power objective, examine individual cells to study the phases of plant mitosis.
Use the camera to take micrographs of at least one cell representing each stage.
Label the micrographs and paste them into a Word document, indicating that they are of mitosis in a
plant cell. Print out the Word document and attach it to the back of your lab.
(a) Interphase – cell contains easily seen nucleus and nucleolus—chromosomes appear as fine dots within the
nucleus
(b) Prophase – cell nucleus enlarged—no longer visible—chromosomes appear as short strands within the
nucleus
(c) Metaphase – chromosomes long and thin strands—chromosomes lined up along cell center and look like a
“spider on a mirror”
(d) Anaphase – two sets of separate chromosomes can be seen—look as if they are being pulled apart from
one another
(e) Telophase/Cytokinesis – chromosomes appear at opposite ends of the cell—middle of cell has line across
center (cell plate) that divides in almost into two new cells
Answer the following questions about each of the phases of the cell cycle and mitosis:
Interphase
•
Locate cells resembling Figure 3. Create an image Answer questions 1-3 while observing these cells.
1. Describe the contents of a nucleus during interphase.
2. Are a nucleolus and nuclear membrane present in the cell?
3. Are the chromosomes easily observed in the nucleus at this time?
Use your textbook for reference while answering questions 4 & 5.
4. Are chromosomes present in cells during interphase?
5. What important event occurs to chromosomes during interphase?
Prophase
•
Locate cells resembling Figure 4. Answer questions 6 & 7 while observing these cells.
6. Are chromosomes now visible during prophase?
7. Describe the changes that have occurred to the nucleolus and nuclear membrane from interphase to
prophase.
Use your textbook for reference while answering question 8.
8. Explain why chromosomes can be observed during prophase but were not observable during interphase.
Metaphase
•
Locate cells resembling Figure 5. Answer questions 9 and 10 while observing these cells.
9. Describe where the chromosomes are now located in relation to the cell.
10. Can evidence of chromosome duplication (replication) now be observed?
11. What is that evidence?
Use your textbook for reference while answering questions 12 & 13.
12. What are the fibers called that become visible during this phase?
Anaphase
•
Locate cells resembling Figure 6. Answer questions 13 & 14 while observing these cells.
13. In metaphase, chromosome pairs were lined up along the cell’s center. Describe what is occurring to
each chromosome pair during anaphase.
14. Toward what area(s) of the cell are the chromosomes being directed during anaphase?
Use your textbook for reference while answering question 15.
15. What structure is responsible for the movement of chromosomes during this phase?
Telophase
•
Locate cells resembling Figure 7. Answer questions 16 & 17 while observing these cells.
16. What cell parts begin to reappear during this phase? (see question 7)
17. Describe the location of the chromosomes now compared to where they were during metaphase.
Daughter Cells
•
Locate cells resembling Figure 8. Answer questions 18 & 19 while observing these cells.
18. What is the name of the process through which the cytoplasm of a cell divides to produce two daughter
cells? How does this process differ in plants and animals?
19. Explain how the number of chromosomes found in each daughter cell compares to the number found in
the original cell before mitosis.
Analysis
20. Explain how the process of cell division helps an organism to grow in size.