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# Calculating osmotic potential

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There was an experiment conducted to determine the osmotic potential of potato tissue.

The osmotic potential of various concentrations of sucrose solutions are provided in the table below.

Sucrose Concentration Osmotic Potential
0.0 M 0.0 MPa
0.1 M -0.245
0.2 M -0.49
0.3 M -.0.735
0.4 M -0.98

A cube of potato tissue was incubated for a set amount of time in various different sucrose solutions, and the weight of the potato tissue determined both before and after incubation. The weight difference shows the amount of water that is either gained or lost by the piece of potato.

The results were as follows

Before After

0.0 M 17.2 g 19.3 g
0.1M 15.7 g 16.9 g
0.2 M 16.5 g 17.5 g
0.3 M 15.7 g 15.9 g
0.5 M 16.7 g 16.7 g

Using this data and the table above, calculate the osmotic potential of potato tissue.

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#### Solution Preview

The key to this problem is to determine the sucrose concentration where there was no weight gain from the potato sample, as this means there was no water transfer to the potato ...

#### Solution Summary

This solution describes a mock experiment to determine the osmotic potential of potato tissue. It takes you through the process needed to calculate the value from experimental data.

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## Tissue water potential

2a. Graph the change in weight versus the concentration of mannitol . Draw on the graph how you would estimate the water potential of the tissue
2b. Graph the change in length versus the concentration of mannitol. Draw on the graph how you would estimate the water potential of the tissue

3. From your graph what do you estimate the water potential of the potato tissue to be

4. Does the increase in tissue weight and length resulting from gaining water in the less negative water potential solutions eventually plateau and reach a maximum? Why? Explain this observation based on what we know about the two potential terms that contribute to total water potential in a plants cell or plant tissue

5. Why would the potato tissue shrink when it loses water (explain this in terms of pressure potential?)?

6. If you were using this technique with a tissue with very rigid, inelastic cell walls (such as a woody tissue) which measurement method would be least effective? why?

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