Potato in sugar solutions — questions

1. identify

Which part of a plant cell is partially permeable, so that it controls the movement of water by osmosis?

Circle one answer.

• The cell wall
• The cell membrane
• The vacuole
• The nucleus

Nudge (only if you are stuck): One layer lets water and solutes straight through; the other lets water through but stops sugar.

2. calculate

A potato cylinder had a mass of 2.40 g. After 30 minutes in a sucrose solution it had a mass of 2.16 g. Calculate the percentage change in mass.

Percentage change in mass: ______________ unit ________

Nudge (only if you are stuck): Change = 2.16 − 2.40. Divide by the starting mass, 2.40 g, then multiply by 100.

3. sequence

Put the steps of the potato investigation in order.

Write the number of each step in order.

1. Cut cylinders of the same size from one potato
2. Blot each cylinder gently and weigh it
3. Put each cylinder into its own solution for 30 minutes
4. Lift each cylinder out and blot it the same way
5. Reweigh each cylinder and calculate the percentage change in mass

• First: ______
• Second: ______
• Third: ______
• Fourth: ______
• Last: ______

Nudge (only if you are stuck): Masses must be recorded before and after soaking, and the surface liquid removed each time.

4. identify

Which variables must be kept the same so that the investigation is a fair test? Select all that apply.

Tick every correct statement.

• Volume of solution in each tube
• Temperature
• Time in the solution
• Concentration of sucrose
• Size of the cylinders

Nudge (only if you are stuck): The concentration of the solution is the variable that is changed on purpose.

5. identify

Match each description of a plant cell to the correct term.

Write the number of the matching option.

1. Turgid
2. Flaccid
3. Plasmolysis
4. Turgor pressure

• The cell contents press on the cell wall: ______
• The cell contents no longer press on the cell wall: ______
• The cytoplasm and cell membrane have pulled away from the cell wall: ______
• The pressure of the cell contents on the cell wall: ______

Nudge (only if you are stuck): Think of the three cell drawings: pressing on the wall, no longer pressing, pulled away.

6. explain

Use the graph of mean percentage change in mass against sucrose concentration. (a) Estimate the concentration at which there is no net movement of water. (b) Explain why the cylinder in water gained mass. (c) Why are percentage changes compared, not changes in grams?

(a) Concentration with no net movement

(b) Why the cylinder in water gained mass

(c) Why percentage change

Nudge (only if you are stuck): Where does the line cross 0 %? For (c), did every cylinder start with exactly the same mass?

7. predict / explain

A florist recuts the stems of two bunches of drooping flowers. One bunch is stood in water; the other is stood by mistake in a strong sugar solution. Predict what happens to each bunch over the next hours, and explain using osmosis and turgor.

Bunch in water

Bunch in strong sugar solution

Nudge (only if you are stuck): Compare the water potential of each liquid with the cell sap in the stem and petal cells.