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LAB: Observing Mitosis
Background:
A single fertilized human egg cell will divide to form 2 cells. These 2 cells will each divide into 2 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. The result of mitosis is 2 diploid cells. Mitosis occurs in 4 phases. There is an interphase between each mitosis phase.
Procedure: .
1. Identify and label AT LEAST ONE of EACH of the following stages of cells in figure 2 by using the brief description provided below. Draw an arrow from the cell and write the correct stage name beside figure 2 below. a. interphase: cell contains easily seen nucleus and nucleolus – chromosomes appear as fine dots within the nucleus b. prophase: cell nucleus enlarged – nucleolus no longer visible – chromosomes appear as short strands within nucleus c. metaphase: chromosomes long and thin strands – chromosomes lined up along cell center and look like
“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: chromosomes appear at opposite ends of the cell – middle of cell has line across center that divides it almost into 2 new cells f. cytokinesis (daughter cells) – appear as cells in interphase but smaller and side by side – actually start of new interphase
FIGURE 1 region of rapidly dividing cells in onion root tip
Microscopic view of onion root tip cells undergoing cell division
FIGURE 2

Analysis:
Answer the following questions about each phase of mitosis ( HINT – You may want to use your textbook and your class notes to help answer these questions):
 INTERPHASE: Refer to Figure 3 while answering the following questions:
1. Are chromosomes present in cells during interphase? _______________
2. What term is used to describe nuclear contents during interphase?
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3. What important event occurs to chromosomes during interphase?
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4. What other important events occur during interphase?
 PROPHASE: Refer to Figure 4 while answering the following questions:
1. Are chromosomes visible during prophase?
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2. Describe the changes that have occurred to the nucleolus and nuclear membrane from interphase to prophase?
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 METAPHASE: Refer to Figure 5 while answering the following questions:
1. Describe where the chromosomes are now located in relation to the cell. _____________________________
2. Can evidence of chromosome duplication (replication) now be observed? ____________________________
3. What are the fibers called that become visible during this phase? ___________________________________
4. What term is used to describe the structure at which each fiber attaches to a chromosome? ____________________
 ANAPHASE: Refer to Figure 6 while answering the following questions:
1. In metaphase, chromosome pairs were lined up along the cell’s center. Describe what is occurring to each chromosome pair during anaphase?
______________________________________________
2. Toward what area of the cell are the chromosomes being directed? ______________________________________
3. What structure is responsible for the movement of chromosomes during this phase? ____________________

 TELOPHASE: Refer to Figure 7 While answering the following questions:
1. What cell parts begin to reappear during this phase (HINT – refer to question #2 under prophase)? ________________________________________________
2. Describe the location of the chromosomes now compared to where they were during metaphase?
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 CYTOKINESIS (DAUGHTER CELLS): Refer to Figure 8 while answering the following questions:
1. How many cells have now formed from an original cell? __________________
2. Explain how the number of chromosomes found in each daughter cell compared to the number found in the original cell before mitosis (HINT – read the introduction)?
_______________________________________________________________
3. Referring to question # 2 above, what is this type of cell called (the term used to refer to a cell that contains both sets of chromosomes after division – exactly the same as the parent cell)? _______________________________________
Mitosis Review:
1. Explain how the process of mitosis helps an organism to grow in size:
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2. Complete Figure 9 to show the structures visible during each stage of mitosis. Draw in AND label the structures listed below on the appropriate diagram. Be sure to label each animal cell with the correct mitosis stage name!
a. Interphase: draw and label nuclear membrane, nucleolus, chromatin, centriole b. Prophase: draw in and label disappearing nuclear membrane, disappearing nucleolus, original chromosomes , chromosome copies c. Metaphase: draw in the 2 chromosome pairs as they would appear during metaphase. Label chromosomes, spindle fibers d. Anaphase: draw in the 2 chromosome pairs as they separate in anaphase. Label centromeres e. Telophase: draw in and label reforming nuclear membrane, reforming nucleolus, pinching in of cell membrane f. Cytokinesis/New Interphase: draw in and label nucleus, nucleolus, nuclear membrane, and chromatin in both cells

FIGURE 9: