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Transcript
Name: __________________________________________________ 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 ______________ _____________ ____________ ___________ OSERVATIONS 1. Describe what is happening in each stage of the cell cycle. __________________________________________________________________________________________________ __________________________________________________________________________________________________ __________________________________________________________________________________________________ __________________________________________________________________________________________________ __________________________________________________________________________________________________ 2. What stage is observed most frequently? __________________________________________________________________________________________________ __________________________________________________________________________________________________ __________________________________________________________________________________________________ 3. How is interphase different from the other stages? __________________________________________________________________________________________________ __________________________________________________________________________________________________ __________________________________________________________________________________________________ 4.What is the color of the chromosomes? Of other cell structures? __________________________________________________________________________________________________ __________________________________________________________________________________________________ __________________________________________________________________________________________________ ANALYSIS AND CONCLUSIONS 1. In which area of the onion root tip do most of the cells appear to be undergoing mitosis? ______________________________________________________________________________ ______________________________________________________________________________ ______________________________________________________________________________ 2. How can you tell that mitosis is a continuous process? ______________________________________________________________________________ ______________________________________________________________________________ ______________________________________________________________________________ 3. Do some stages of the cell cycle occur more frequently than others? Identify the stage(s) and explain why. ______________________________________________________________________________ ______________________________________________________________________________ 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? ____________________________________________________________________________ ____________________________________________________________________________ ____________________________________________________________________________ 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? ____________________________________________________________________________ ____________________________________________________________________________ ____________________________________________________________________________ ____________________________________________________________________________ ____________________________________________________________________________ ____________________________________________________________________________ 3. Why is mitosis more readily observed in an onion root tip than in other parts of the root? ____________________________________________________________________________ ____________________________________________________________________________ ____________________________________________________________________________ 4. How does the heredity of a cell formed by mitosis compare to the heredity of the parent cell? Explain. ____________________________________________________________________________ ____________________________________________________________________________ ____________________________________________________________________________ ____________________________________________________________________________ 5. Your muscle cells, nerve cells, and skin cells, look and function differently. Do they contain the same genetic material? How do you know? ____________________________________________________________________________ ____________________________________________________________________________ ____________________________________________________________________________ ____________________________________________________________________________