Homework 3

# Homework 3 - mass)/initial mass 3.02 3.78 0.2 3.11 3.25 0.4...

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BIOL116B SPRING 2008 Homework Due 3/12/08 You are performing an experiment to determine the osmolarity inside a plant cell (specifically potato). Osmolarity refers to the number of dissociated particles that are present in water. For sucrose, that cannot ionize in water 1 mole of sucrose has an osmolarity of 1 osmoles. For NaCl, that can ionize in to Na+ and Cl-, 1 mole of NaCl has an osmolarity of 2 osmoles. Suppose that you take core samples of potato and measure the mass of each potato core. You then place them into beakers that contain sucrose solutions of different concentrations. You cover the beakers and let them sit overnight. The next day you remove each core sample, dry the outside, and measure its mass again. Below are the data you obtain. Sucrose concentration (Mole/L) Initial potato core mass (g) Final potato core mass (g) % mass change = (initial mass – final
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Unformatted text preview: mass)/initial mass 3.02 3.78 0.2 3.11 3.25 0.4 2.86 2.51 0.6 2.89 2.27 0.8 2.95 2.16 1.0 3.07 2.20 1. (2 pt) Fill in the table above. Then, construct a graph (with axes correctly labeled) showing the % mass change versus sucrose concentration. Attach the graph to this page. 2. (2 pt) In terms of osmosis, explain why some potato cores gained weight and others lost weight. 3. The osmolarity of the potato would be the sucrose concentration that is isotonic relative to cytoplasm of the potato cells. A. (1.5 pt) What mass change would be equivalent to an isotonic solution? Why? B. (0.5 pt) Based on your graph, what is the osmolarity of potato cells? 4. (2 pt) In lab, you learned that the animal cells have an osmolarity equivalent to 0.9% NaCl. What is the osmolarity of 0.9% NaCl? (Hint: Be sure to read the paragraph at the top of this homework). Show your work....
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