Tutopiya: Study Resources for IGCSE, IB, GCSE & A-Levels

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5 MCQs

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1
What does diffusion involve?
Answer & explanation
Correct: option B
Diffusion is passive movement DOWN the gradient (high to low). No energy needed.
2
Which change would INCREASE the rate of diffusion across a membrane?
Answer & explanation
Correct: option C
Steeper gradient = more particles moving down per second. Rate also increases with higher temperature, larger SA and thinner membrane (shorter distance).
3
A cube has sides of 3 cm. What is its surface area to volume ratio?
Answer & explanation
Correct: option B
SA = 6 × 3² = 54 cm². V = 3³ = 27 cm³. Ratio = 54/27 = 2:1.
4
Which adaptation of the alveoli reduces the diffusion DISTANCE?
Answer & explanation
Correct: option B
Thin walls = short diffusion distance. The other three relate to SA, gradient and ventilation respectively.
5
Why do larger organisms need specialised exchange surfaces?
Answer & explanation
Correct: option B
Big organisms have a low SA:V ratio — surface diffusion alone is too slow to meet their needs. Hence lungs, gills, gut villi etc.