Pupil sheet · Diffusion and active transport

Diffusion and cell size — questions

Name ______________________ Date ____________

Try every question before you use a nudge. Write in full sentences where you are asked to explain.

1. define

Which statement describes diffusion?

Circle one answer.

Movement of particles from low to high concentration, using energy from respiration
Net movement of particles from higher to lower concentration, as a result of their random movement
Movement of water only, through a membrane
Particles moving in one direction only, towards where there is more space

Nudge (only if you are stuck): Think of the purple colour spreading through still water: which way is the overall movement, and what makes the particles move?

2. calculate

A cube of agar has sides of 3 cm. Calculate (a) its surface area, (b) its volume and (c) its surface area to volume ratio.

(a) Surface area: ______________ unit ________

(b) Volume: ______________ unit ________

Nudge (only if you are stuck): Surface area: 6 faces, each 3 cm × 3 cm. Volume: 3 cm × 3 cm × 3 cm. Ratio: surface area ÷ volume.

3. explain

In the experiment, every cube gained a colourless border of about the same width in 4 minutes. Explain why the 0.5 cm cube was colourless all through but the 2 cm cube still had a large pink core.

Nudge (only if you are stuck): How far is the centre of each cube from its surface?

4. state

Which changes would make a 1 cm agar cube clear (go colourless all through) in a shorter time? Choose all that apply.

Tick every correct statement.

Warmer acid
More concentrated acid
A smaller cube
Colder acid
A bigger cube

Nudge (only if you are stuck): Two changes make the particles cross into the agar faster; one gives them less distance to go.

5. explain

A drop of food colouring spreads through a glass of still water. After a day the colour is the same everywhere. Are the particles of colouring still moving? Explain.

Nudge (only if you are stuck): Do particles stop moving when the concentration is even?

6. suggest / explain

An amoeba is a single-celled organism about 0.5 mm across. It takes in oxygen through its surface. Suggest why an amoeba can rely on diffusion alone, but an animal the size of a mouse could not.

Nudge (only if you are stuck): Compare the distance from the surface to the centre, and the surface for each unit of volume.