1.13 Diffusion
7 exam questions worth 16 marks. Write your answer, open the mark scheme, then give yourself the marks you earned. Your answers are saved on this device.
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Which of these is an example of diffusion?
Choose one answer.
Correct Not quite: the answer is Oxygen moving from the alveoli into the blood
Mark scheme
A (Oxygen moving from the alveoli into the blood)
Model answer
A: Oxygen moving from the alveoli into the blood. Oxygen moves down its concentration gradient from the alveoli (high) to the blood (low).
Define diffusion.
Mark scheme
- the (net) movement of particles (1)
- from a region of higher concentration to a region of lower concentration / down a concentration gradient (1)
Model answer
Diffusion is the net movement of particles from a region of higher concentration to a region of lower concentration, down a concentration gradient.
Name two substances that move into or out of cells by diffusion.
Mark scheme
Any two from:
- oxygen (1)
- carbon dioxide (1)
- urea (1)
- allow water / glucose / amino acids
Model answer
Oxygen and carbon dioxide.
Explain why diffusion happens faster at a higher temperature.
Mark scheme
- the particles have more (kinetic) energy (1)
- so they move faster (1)
- so more particles move across / more collisions per second (1)
Model answer
At a higher temperature the particles have more energy, so they move faster. This means that more particles spread out or cross the membrane in a given time.
Particles of a dye are placed in one corner of a beaker of water. After a long time they are evenly spread throughout the water.
Explain why there is no net movement of particles once they are evenly spread.
Mark scheme
- the concentration is the same everywhere / there is no concentration gradient (1)
- the particles still move, but equal numbers move in each direction (1)
Model answer
There is no concentration gradient once the particles are evenly spread. The particles still move at random, but the same number move in each direction, so there is no net movement.
A student times how long it takes the colour to spread through a piece of agar. The colour moves 12 mm in 4 minutes.
Calculate the mean rate of diffusion in mm per minute.
Mark scheme
- 12 ÷ 4 (1)
- = 3 (mm per minute) (1)
- allow 3 for 2 marks with no working
Model answer
rate = distance ÷ time = 12 ÷ 4 = 3 mm per minute.
Describe how oxygen gets from the air in the lungs into the blood, and explain why it moves in this direction.
Mark scheme
- oxygen is at a higher concentration in the air in the alveoli than in the blood (1)
- so it moves by diffusion (1)
- down a concentration gradient (1)
- across the (thin) wall of the alveolus into the blood capillary (1)
Model answer
The concentration of oxygen is higher in the air in the alveoli than in the blood. Oxygen therefore moves by diffusion, down its concentration gradient, across the thin wall of the alveolus and into the blood in the capillary.
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