Tonicity of Potato Cells

Biology 12 Tonicity of Potato Cells Lab

Problem What is the approximate the sugar concentration of potato cells?

Introduction A cell maintains equilibrium with its surroundings primarily by taking in or expelling water through the process of osmosis. Osmosis is the movement of water across the cell membrane. The direction the water moves, either into or out of the cell, is determined by the difference in concentration between the inside of the cell and the outside of the cell.

Three situations are possible: - If the outside solution is equal in concentration to the inside of the cell, the solution is isotonic. - If the outside solution is lower in concentration to the inside of the cell, the solution is hypotonic. - If the outside solution is higher in concentration to the inside of the cell, the solution is hypertonic.

Potatoes cells contain a significant amount of dissolved sugar. The goal of this lab is to determine the internal sugar concentration of a potato cell.

Hypothesis Write a hypothesis for this lab. What do you predict will happen to the potato in each solution? ______

Variables Manipulated______Responding______Controlled variables______.

Materials - 6 potato pieces - 6 test tubes - 6 sugar solutions (0.0 M, 0.2 M, 0.4 M, 0.6 M, 0.8 M, 1.0 M) - Electronic balance - 1 marking pen - 1 weigh boat - 1 test tube rack

1 Procedure Day 1:

1. With a pencil, label each of six test tubes with the sugar solution concentration you will put in it. 0.0M, 0.2M, 0.4M, 0.6M, 0.8M, 1.0M. 2. Produce six tissue samples at least 3 cm in length from the potatoes provided. Be sure that each sample has a uniform shape and is not missing any tissue. 3. Trim each tissue sample to 3 cm and remove any potato skin.. Record the length measurement for each sample in Table 1. 4. Measure the diameter of each tissue sample and record this value in Table 1. Be sure to keep your samples separated. To avoid confusion, only have one sample out of the test tube at a time. 5. Use the electric scale to determine the mass of each sample. tare the scale before collecting your mass data. Record this value in Table 1. 6. With a graduated cylinder, measure out 7 ml of 0.0M sucrose and pour this solution into the 0.0M test tube. Repeat for each solution. 7. Cover the top of each test tube with a square of aluminum foil and store them in your test tube rack until tomorrow. 8. Calculate the volume of each tissue sample and record this value in Table 1.

Procedure Day 2:

1. Determine the length, mass and volume of each tissue sample. To avoid confusion, only have one sample out of the test tube at a time. Do not let the samples set on your lab towels or bench top for too long or they will begin to dry out and affect your results. 2. Once you are finished collecting your data, dispose of your tissue samples and wash your test tubes. 3. Calculate the length, mass, and volume differences between Day 2 and Day 1. Since you are subtracting Day 2 – Day 1, you may produce negative values. 4. Graph the differences of mass, and volume between Day 2 and Day 1 versus your solution concentrations. Be sure to include a title, labeled axes, and units on both of your graph.

2 Observations

Table 1.______

0.0M 0.2M 0.4M

Soln Soln Soln

Day 2 Day 1 Diff Day 2 Day 1 Diff Day 2 Day 1 Diff Measurements Length (cm) Mass (g) Diameter (cm) Radius (cm) Volume (cm3)

Description

0.6M 0.8M 1.0M

Soln Soln Soln

Day 2 Day 1 Diff Day 2 Day 1 Diff Day 2 Day 1 Diff Measurements Length (cm) Mass (g) Diameter (cm) Radius (cm) Volume (cm3)

Description

Analysis Questions 3 On a separate sheet of paper draw your two graphs for change in mass, change in volume and answer the following questions.

1. What is diffusion?

2. Compare and contrast diffusion and osmosis.

3. Why did the mass of the cuboidal change in each solution? Explain using the terms hypotonic, hypertonic, and isotonic and describe which way water was flowing.

4. Why did the length of the cuboidal change in each solution?

Conclusion  Use your data/graph to answer the Problem.  Be sure to explain why some pieces increased/decreased/did not change in mass.