LAB: OSMOSIS IN POTATO CELLS - ultimate cool things



BIOLOGY LAB: OSMOSIS IN POTATO CELLS

Pre-Lab: Write the following instructions for the preparation of sucrose solutions on the Pre-Lab page.

To prepare dilutions: (“M” = molar concentration)

1. Put “x” mL 1M sucrose solution in a 10mL graduated cylinder.

2. Add distilled water to 10mL mark.

Example: 0.8M sucrose solution = 8 mL 1 M sucrose + 2 mL distilled water

Background Information: Explain how plant cells maintain homeostasis. Describe the relationship between diffusion and osmosis and how they are affected by the concentration gradient (difference).

Objective: To observe the effects of different concentrations of sucrose solutions on the mass of a potato cell.

Hypothesis: (Predict how molar concentration of sucrose will influence the mass of a potato cell.)

Materials:

potato balance scalpel 10 mL graduated cylinder

six test tubes cork borer ruler Sucrose solutions:

test tube rack test tube brush distilled water (0.2, 0.4, 0.6, 0.8, 1Molar)

Procedure:

1. Pour 10 mL of each of the following solutions into six labeled test tubes:

0.2M, 0.4M, 0.6M, 0.8M, 1M sucrose and distilled water.

2. Use the cork borer to obtain a complete, undamaged potato cylinder.

Use the scalpel to cut the cylinder to two centimeters in length.

(Be sure to remove the peel!) You will need six potato cylinders cut

in the same manner and of the same length.

3. Use the balance to measure the mass of each potato cylinder.

Record the mass in your data table.

4. Place one cylinder in each of the solutions. Let stand overnight.

5. Remove the potato cylinders from the solutions and carefully drain

on a paper towel. (Don’t forget which cylinder came out of which

concentration of sucrose solution!!!)

6. Use the balance to measure the mass of each potato cylinder.

Record the mass in your data table.

Results:

1. Record at least three written observations.

2. Record your data in a table that shows: sucrose solution concentration, initial mass of the potato

cylinder, final mass of the potato cylinder, change in mass, and percent change in mass.

3. Graph the sucrose concentration (independent variable) vs. the percent change in mass of the

potato cylinders (dependent variable). (Be sure to include a brief description of your line graph.)

Calculations: Use the following formula to calculate the percent change in mass of the potato cylinders. Show all calculations.

% change = final mass – initial mass X 100

initial mass

Source of Error: Identify and explain any unexpected results.

Analysis Questions:

1. Identify the independent variable in this lab.

2. Identify the dependent variable in this lab.

3. Use your graph to determine the concentration of a solution where there would be no net change in the mass

of the potato.

4. At what concentration is there the least percent change in mass?

5. If there had been no net change in the mass of the potato sections, what term would describe the

sucrose solution the potatoes were placed in?

6. What happens to the mass of the potatoes in the 0.8M sucrose? What term would describe this sucrose

solution?

7. What happens to the mass of the potatoes in water or very dilute sucrose solutions? What term

would describe these solutions in comparison to the cellular components of the potato?

8. Describe the feeling of the potatoes in the water and compare it to how the potatoes in the 0.8M

sucrose feel. What term reflects the change you are feeling in the potatoes?

9. Considering the potato at the cellular level, explain the similarity of what happened to the potato cells in a

concentrated sucrose solution with what happened to the Elodea cells when salt water was added.

10. Explain why a person who drinks salt water at sea goes crazy. Include the brain cell membrane and the term

“osmosis” and at least one of the following: “hypertonic”, “hypotonic”, or “isotonic” in your explanation.

Conclusion: Briefly summarize the procedure and explain the effects of different concentrations of sucrose solutions on the potato core. Explain whether or not your results support your hypothesis. Include an explanation

of how the cell membrane maintains homeostasis. It must be written in the third person.

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