iGCSE Biology (0610)-3.2 Osmosis - iGCSE Style Questions Paper 3

Question

Water moves into and out of cells by osmosis.

(a) State two plant cell structures that water moves through to reach the cytoplasm.

(b) Potato plant tissue was used to investigate osmosis.

Potato cylinders were placed into different sucrose solutions for 30 minutes.

The masses of the potato cylinders were measured before and after being placed into the solutions.

The difference in mass was calculated for each potato cylinder.

Table 2.1 shows the results of the investigation.

(i) Using the information in Table 2.1, calculate the percentage change in mass for the potato cylinder in the 0.6 mol per dm³ sucrose solution.

Give your answer to two decimal places.

(ii) Describe the expected appearance of the potato cylinder that was placed in the 0.8 mol per dm³ sucrose solution for 30 minutes.

(iii) Using the results in Table 2.1, describe how the concentration of sucrose solution affects the percentage change in mass of the potato cylinders.

▶️ Answer/Explanation

Solution

(a) cell wall ; cell membrane

Explanation: Water moving into plant cells must pass through two key structures. First, it passes through the cell wall, which is a permeable outer layer that provides structural support. Then it moves through the cell membrane (also called plasma membrane), which is selectively permeable and controls what enters and leaves the cell. These two structures work together to regulate water movement while maintaining the cell’s structure.

(b)(i) (~)3.91(%)

Explanation: To calculate the percentage change in mass:
1. Identify the starting mass (2.30g) and final mass (2.21g)
2. Calculate the difference: 2.21 – 2.30 = -0.09g
3. Calculate percentage change: (difference/starting mass) × 100
= (-0.09/2.30) × 100 = -3.913%
4. Round to two decimal places: -3.91%
This negative value indicates the potato lost mass in this solution.

(b)(ii) smaller / shorter / shrunken

Explanation: In the 0.8 mol/dm³ sucrose solution, the potato cylinder would appear visibly smaller or shrunken. This happens because the solution is hypertonic compared to the potato cells – it has a higher solute concentration than the cell cytoplasm. Water moves out of the potato cells by osmosis, causing the cells to lose water and become flaccid. As many cells lose water, the entire cylinder shrinks in size.

(b)(iii) As the concentration of sucrose solution increases, the percentage change in mass decreases / the lower the concentration, the more percentage change in mass.

Explanation: The data shows a clear trend:
– In dilute solutions (0.0-0.4 mol/dm³), the percentage change is positive (potatoes gain mass) because water enters the cells by osmosis.
– In concentrated solutions (0.6-0.8 mol/dm³), the percentage change is negative (potatoes lose mass) because water leaves the cells.
– The higher the sucrose concentration, the greater the water loss (or less water gain), showing an inverse relationship between sucrose concentration and mass change.
This demonstrates how osmosis causes water to move from areas of low solute concentration to high solute concentration.

Question

(a) Water is an important biological molecule. The box on the left contains the word ‘Water’. The boxes on the right contain some sentence endings.

Draw a line from the box on the left to each correct statement about water. Draw three lines.

(b) Students investigated the movement of water in model animal cells using dialysis tubing. Fig. 1.1 is a diagram of the apparatus used in the investigation.

(i) State the name of the part in Fig. 1.1 which represents:

the partially permeable membrane of an animal cell …………. .
the cytoplasm of an animal cell ………. .

(ii) Draw an arrow on Fig. 1.1 to show the direction of water movement during the investigation.

(iii) State the name of the process of water diffusing across a partially permeable membrane.

(c) Animal cells placed in pure water will burst. State the structure that prevents a plant cell from bursting when it is placed in pure water.

▶️ Answer/Explanation

Solution

Ans:

(a) Correct matches for water properties:

(b)(i) – Partially permeable membrane: Dialysis tubing (selectively allows water to pass). – Cytoplasm: Water inside the tubing (represents cell contents).

(b)(ii) Arrow direction: From water (inside tubing) → salt solution (osmosis occurs toward higher solute concentration).

(b)(iii) The process is osmosis (passive diffusion of water across a membrane).

(c) Plant cells resist bursting due to their rigid cell wall, which counteracts osmotic pressure.

iGCSE Biology (0610)-3.2 Osmosis – iGCSE Style Questions Paper 3

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