Water Potential ( Topic 2)

Question 1

What factors affect the rate of osmosis?

Answer 1

1. Temperature.
2. Surface area.
3. Thickness of the membrane.
4. Water potential.

Question 2

What is the independent variable?

Answer 2

The sucrose concentration of the solution.

Question 3

What variables should be controlled and how?

Answer 3

1. Temperature: Place the test tubes containing the potato cylinders in a water bath.
2. Surface area: Use a cork borer to cut out potato cylinders and then use a scalpel to cut them all to the same length.
3. Water potential inside the potato cells: Cut all the cylinders from the same potato.

Question 4

Why should you blot the potato cylinder dry?

Answer 4

So that any water on the outside of cells is absorbed and will not affect the calculation of the initial mass.

Question 5

Why do you have to record both the initial mass and the final mass?

Answer 5

1. So that a change in mass can be calculated.
2. Any change in mass will be due to the loss of water.

Question 6

What will be the axis of the graph that you plot?

Answer 6

X-axis: The sucrose concentration of the solution.
Y-axis: The percentage change in mass.

Question 7

What is the general trend shown in the graph?

Answer 7

As the sucrose concentration increases, the percentage change becomes more negative. This is because the water potential of the solution will become lower compared to that in the cells, meaning more water will move out of the cell via osmosis. This means the final length will be smaller compared to the initial length.