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CAIE IGCSE Biology 3.1 Diffusion Questions

Practise defining diffusion as random kinetic movement down a concentration gradient, tracing it across membranes and exchange surfaces, and predicting its rate factors.

Syllabus
2026–2028
Course
Biology 0610

Exam points

  • Define diffusion as the net movement of particles down a concentration gradient caused by random kinetic motion, and show the direction of movement for gases or solutes.
  • Apply diffusion across cell membranes and exchange surfaces, distinguishing it from osmosis and active transport and using membrane-permeability evidence.
  • Explain why diffusion is important for gas exchange and cell supply or waste removal, tracing pathways through stomata, air spaces, alveoli or cell membranes.
  • Predict how surface area, temperature, concentration gradient and diffusion distance affect rate, including interpretation of linked experiment graphs.

Covered syllabus points

3.1.1—Diffusion3.1.2—Energy for diffusion comes3.1.3—Diffusion through cell membranes3.1.4—Importance of diffusion3.1.5—Factors that influence diffusion

Question 1

[Maximum number: 1]

Diffusion may be defined as the net movement of particles from a region of their ...... 1……1 \ldots \ldots concentration, to a region of their ...... 2…..2 \ldots . .. concentration where movement is 3..... a concentration gradient.

Which words complete gaps 1,2 and 3 ?

1

2

3

higher

lower

down

higher

lower

up

lower

higher

down

lower

higher

up

Question 2

[Maximum number: 4]

Fig. 1.1 shows the movement of particles through an epithelial cell in the small intestine.

Fig. 1.1

Fig. 1.1

Question (a)

(a)

In Fig. 1.1, arrow P represents the diffusion of oxygen molecules.

[ 3 ]

Question (i)

(i)

Describe what is meant by the term diffusion.

[ 2 ]

Question (ii)

(ii)

State the type of energy needed for diffusion.

[ 1 ]

Question (b)

(b)

Carbon dioxide molecules also move by diffusion.

[ 1 ]

Question (i)

(i)

On Fig. 1.1, draw an arrow to show the direction of diffusion of carbon dioxide molecules.

[ 1 ]

Question 3

[Maximum number: 1]

How do carbon dioxide and oxygen move into and out of a mesophyll cell?

A

active transport

B

diffusion

C

respiration

D

transpiration

Question 4

[Maximum number: 1]

Fig. 1.1 shows the movement of particles through an epithelial cell in the small intestine.

Fig. 1.1

Fig. 1.1

In Fig. 1.1, arrow P represents the diffusion of oxygen molecules.

State the type of energy needed for diffusion.

Question 5

[Maximum number: 1]

The diagram shows a section through an alveolus and through a capillary.

Figure for Question 5 — CAIE IGCSE Biology

How does carbon dioxide move from Y to X ?

A

by diffusion

B

by osmosis

C

by translocation

D

by transpiration

Question 6

[Maximum number: 4]

Question (a)

(a)

Fig. 1.1 is a micrograph of part of some fish gills.

Fig. 1.1

Fig. 1.1

Fish gills are adapted for gas exchange by diffusion.

[ 1 ]

Question (i)

(i)

Suggest one adaptation, visible in Fig. 1.1, that shows that fish gills are efficient structures for gas exchange by diffusion.

[ 1 ]

Question (b)

(b)

Some pollutants decrease the concentration of dissolved oxygen in rivers. This can result in the death of fish.

[ 3 ]

Question (i)

(i)

Researchers investigated the effect of the concentration of dissolved oxygen in water on gas diffusion distance in tissues. The thickness of fish gills was used to determine the gas diffusion distance.

The researchers changed the concentration of dissolved oxygen by bubbling different concentrations of oxygen into water. The temperature of the water was kept constant at 15∘C15^{\circ} \mathrm{C}.

Their results are shown in Fig. 1.2.

Fig. 1.2

Fig. 1.2

Fig. 1.3 shows the relationship between the concentration of dissolved oxygen and water temperature.

Fig. 1.3

Fig. 1.3

Complete steps 1 to 3 to determine the effect on gas diffusion distance of increasing the temperature of the water from 15∘C15^{\circ} \mathrm{C} to 25∘C25^{\circ} \mathrm{C}.

Step 1
Find the concentration of dissolved oxygen from Fig. 1.3 at:
15∘C15^{\circ} \mathrm{C} : mg per dm3\mathrm{dm}^{3}25∘C25^{\circ} \mathrm{C} : mg per dm3\mathrm{dm}^{3}

Step 2
Use the values from step 1 to find the gas diffusion distances from Fig. 1.2: μm\mu \mathrm{m}μm\mu \mathrm{m}

Step 3
Calculate the difference in the values from step 2. μm\mu \mathrm{m}

[ 3 ]
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