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NAME ________________________________ LAB CYCLOSIS (Cytoplasmic Streaming) IN ELODEA INTRODUCTION Green plant cells contain special structures called chloroplasts (p. 65). Chloroplasts are cytoplasmic organelles that function in manufacturing/synthesizing plant food (i.e., glucose). Chloroplasts are green because they contain the green pigment chlorophyll. This pigment has an important job of absorbing sunlight energy during a complex chemical process called photosynthesis. Photosynthesis entails capturing and transforming the energy of sunlight into chemical energy. This chemical energy is found in the chemical bonds of glucose. Elodea is a leafy flowering plant commonly found in aquariums. Its leaves are thin and transparent; most of them are only 2 cell layers thick. New leaves are produced at the tip of the plant. You will examine one or more of these thin leaves in this laboratory investigation. MATERIALS Compound light microscope, slides, coverslips, methylene blue, Elodea leaf METHODS 1. 2. 3. 4. 5. 6. 7. 8. 9. Tear an Elodea leaf in half. Prepare a slide of one of the leaf portions. DO NOT ADD WATER (i.e., no wet mount). Examine the cells under both LOW & HIGH power. Observations: Note the shape of the cells, the presence of cell walls, and the shape & location of the chloroplasts. Sketch the cells under LOW & HIGH power. Label the cell wall & chloroplasts. Determine the size of an individual cell. Assume HIGH power FOV is 300 µm. Observations: Examine the cells carefully for any occurrence of cyclosis (or cytoplasmic streaming). Cyclosis is the movement of the cytoplasm. Try to find cells where the chloroplasts are moving. This is an indication that the cytoplasm is moving. Remove the wet mount slide from the stage. Stain the Elodea cells by placing ONE drop of methylene blue at one edge of the coverslip. Draw it under the coverslip by placing a piece of paper towel to the opposite edge. Observe the cells again under LOW & HIGH power to see if any additional structures are visible. Sketch the stained cells under HIGH power. Label the cell wall, chloroplasts, cell membrane (if visible), nucleus, nucleolus, and the large vacuole (if visible). RESULTS Observations Estimated cell size (in µm) 3 sketches – 1 under LOW & 2 under HIGH power. LABEL the stained HIGH power sketch. Shape of Elodea cells? __________________________ Cell wall present…Yes or No? _______ Shape of chloroplasts? _________________ Location of chloroplasts? __________________ Did you observe cyclosis…Yes or No? _______ If yes, where were the chloroplasts moving? _________________________________ Estimated size of a single Elodea cell? ________ µm ELODEA CELLS LOW (unstained) HIGH (unstained) HIGH (stained) DISCUSSION 1. What is cyclosis AND why is it important to cells? ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------2. If you were to focus up and down on one particular cell (using the fine adjustment knob), why would some chloroplasts come into view while others would go out of view? --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------3. What role do chloroplasts play during photosynthesis? ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------4. Why would it be advantageous to have Elodea in a balanced aquarium? --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------5. What additional structure could be seen after the cells were stained with methylene blue? ----------------------------------------------------------------------------------------------------------------------6. Why do you think the chloroplasts moved only around the edges of the cells? --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------7. Most plants store their excess glucose as one of two possible polysaccharides. One is cellulose, a key component of their cells walls. What is the other & where is it located? ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------