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CAIE IGCSE Biology 3.1.5 Factors Affecting Diffusion

Practise predicting and investigating how surface area, temperature, concentration gradient and distance change diffusion rate.

Syllabus
2026–2028
Course
Biology 0610

Exam points

  • predict faster diffusion with a larger area, higher temperature, steeper gradient or shorter distance
  • read linked graphs to determine how temperature changes oxygen concentration and gas diffusion distance

3.1.5—Factors that influence diffusion question 1

[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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