Question 1 Medium
Does a larger organism have a larger or smaller surface area to volume ratio than a small one?
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Answer: smaller
- Volume increases faster than surface area.
- So the ratio is smaller.
Diffusion and exchange surfaces: GCSE Combined Science Biology practice questions
A second set of questions on diffusion and exchange surfaces. They are different from the ones on the topic page. Try each, then open the answer and compare your working.
More questions
Question 2 Medium
A solution is heated. Does the rate of diffusion increase or decrease?
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Answer: increase
- Heat gives particles more energy.
- They move faster, so diffusion speeds up.
Question 3 Medium
Calculate the volume of a cube with sides of 3 cm, in cm³.
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Answer: 27 cm³
- Volume = side × side × side.
- 3 × 3 × 3 = 27.
Question 4 Medium
Calculate the surface area of a cube with sides of 1 cm, in cm².
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Answer: 6 cm²
- A cube has 6 faces.
- 6 × 1 × 1 = 6.
Question 5 Hard
Calculate the surface area to volume ratio of a cube with sides of 4 cm. Give it as n : 1.
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Answer: 1.5 : 1
- Surface area = 6 × 16 = 96, volume = 64.
- 96 ÷ 64 = 1.5.
Question 6 Hard
Why are the walls of the alveoli only one cell thick? Give the word that describes the distance.
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Answer: short
- A thin wall means gases do not have far to go.
- The diffusion distance is short.
Question 7 Hard
A cube of side 1 cm and a cube of side 2 cm are compared. Which has the larger surface area to volume ratio?
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Answer: the 1 cm cube
- The 1 cm cube has a ratio of 6 : 1.
- The 2 cm cube has a ratio of 3 : 1.
Question 8 Hard
Blood flows past the alveoli and removes oxygen. What does this do to the concentration gradient?
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Answer: keeps it steep
- Oxygen is carried away, so blood concentration stays low.
- The gradient stays steep.
Quick checks
Short questions with options. Choose one before you open the answer.
Check 1
What is diffusion?
Show answer
The net movement of particles from a region of higher concentration to a region of lower concentration.
Check 2
Does diffusion need energy from the cell?
Show answer
No. It is a passive process.
Check 3
Give three factors that affect the rate of diffusion.
Show answer
Concentration gradient, temperature and surface area.
Check 4
Why does a higher temperature speed up diffusion?
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Particles have more kinetic energy, so they move faster.
Check 5
Which gas diffuses into cells for respiration?
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Oxygen.
Check 6
Which waste substance made in cells diffuses into the blood plasma?
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Urea.
Check 7
Which gas diffuses out of cells during respiration?
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Carbon dioxide.
Check 8
What is the surface area of a cube with sides of 2 cm?
Show answer
24 cm².
Check 9
What is the volume of a cube with sides of 2 cm?
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8 cm³.
Check 10
What happens to the surface area to volume ratio as an organism gets larger?
Show answer
It gets smaller.
Check 11
Why do large organisms need exchange surfaces?
Show answer
Their surface area to volume ratio is too small for diffusion across the outside to be enough.
Check 12
Name three features of a good exchange surface.
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A large surface area, thin walls and a good blood supply.
Check 13
What are the air sacs in the lungs called?
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Alveoli.
Check 14
What are the folds in the small intestine wall called?
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Villi.
Check 15
Why does breathing keep the gradient steep in the lungs?
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Ventilation brings in fresh air with a high oxygen level.
Check 16
Why does blood flow keep the gradient steep at an exchange surface?
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It carries the diffused substance away, so its concentration stays low.
Check 17
What does concentration mean?
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How crowded the particles of a substance are in a space.
Check 18
What is a concentration gradient?
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The difference in concentration between two places.
Check 19
What is net movement?
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The overall movement of particles in one direction.
Check 20
What is kinetic energy?
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The energy of movement.
Check 21
What is the formula for the surface area of a cube?
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6 × side × side.
Check 22
What is the formula for the volume of a cube?
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Side × side × side.
Check 23
Which comes first in a surface area to volume ratio?
Show answer
The surface area.
Check 24
Why can very small organisms rely on diffusion across their surface?
Show answer
They have a large surface area to volume ratio.
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