Diffusion and active transport — final check

1. calculate / explain

Two agar cubes are put in the same acid. Cube P has sides of 1 cm; cube Q has sides of 4 cm. (a) Calculate the surface area to volume ratio of cube Q. (b) Which cube clears first? Give two reasons.

(a) Surface area : volume of Q: ______________ unit ________

(b) Which cube clears first? Give two reasons.

2. describe / explain

A pupil timed how long 1 cm agar cubes took to clear in the same acid at three temperatures: 10 °C, 18 minutes; 20 °C, 12 minutes; 30 °C, 8 minutes. (a) Describe the pattern. (b) Explain it in terms of particles. (c) Name two variables the pupil must keep the same.

(a) The pattern

(b) Explanation with particles

(c) Two variables kept the same

3. explain

A leaf is kept in the dark. It cannot photosynthesise, but its cells still respire. (a) In which direction does oxygen diffuse through the stomata? (b) In which direction does carbon dioxide diffuse? (c) Explain your answer to (b).

(a) Oxygen

(b) Carbon dioxide

(c) Explanation

4. explain

Cells of a seaweed contain iodide ions at a concentration thousands of times higher than in the sea water around them. (a) Name the process the cells use to take in iodide ions. (b) Describe the part played by carrier proteins in the cell membrane. (c) Explain why the uptake decreases if the cells are short of oxygen.

(a) The process

(b) Carrier proteins

(c) Why oxygen matters