Download OBSERVING ONION ROOT TIPS

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OBSERVING ONION ROOT TIPS
BACKGROUND INFORMATION
When a cell divides, its cytoplasm is split and shared between two new cells. The nucleus, however,
cannot be split and shared. Because the nucleus contains vital information on chromosomes that enables a cell
to carry out its life functions, each new cell needs a complete set of chromosomes. When a cell begins to divide,
the chromosomes are duplicated. Two complete sets of chromosomes are produced. Then, the chromosomes are
distributed between the two cells so that each new cell gets a complete set. Division of the nucleus, including
duplication and sorting of chromosomes, is called mitosis. The process of mitosis occurs in a sequence of steps
or phases. These phases are visible under the microscope in the rapidly growing cells found in an onion root tip.
In this laboratory exercise, you will examine the phases of mitosis in an onion root tip.
PROBLEM
What are the stages of the cell cycle in a plant cell?
MATERIALS
- Microscope
- Prepared slide of onion root tip
PROCEDURE
1. Obtain prepared slide of onion root tip.
2. With the microscope, examine the onion root tip under low power to find cells in various stages of the
cell cycle. After you have located the various stages of the cell cycle under low power, switch to
medium power and refocus microscope. Draw and label a cell from each stage of the cell cycle. Be sure
to identify each stage
Interphase
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OSERVATIONS
1. Describe what is happening in each stage of the cell cycle.
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2. What stage is observed most frequently?
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3. How is interphase different from the other stages?
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4.What is the color of the chromosomes? Of other cell structures?
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ANALYSIS AND CONCLUSIONS
1. In which area of the onion root tip do most of the cells appear to be undergoing mitosis?
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2. How can you tell that mitosis is a continuous process?
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3. Do some stages of the cell cycle occur more frequently than others? Identify the stage(s) and explain
why.
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CRITICAL THINKING AND APPLICATION
1. In one experiment, a substance was applied to an onion root tip that prevented separation of chromatids
during mitosis. What effect would this have on the growing root?
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2. Explain how the chromosomes are sorted during mitosis. How is the sorting process related to the
changes you observed during the phases of mitosis?
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3. Why is mitosis more readily observed in an onion root tip than in other parts of the root?
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4. How does the heredity of a cell formed by mitosis compare to the heredity of the parent cell? Explain.
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5. Your muscle cells, nerve cells, and skin cells, look and function differently. Do they contain the same
genetic material? How do you know?
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