1. 1
   A drop of purple potassium permanganate solution is placed at the bottom of a beaker of still water. Over the next hour, the purple colour spreads evenly throughout the water without any stirring.

   (a)

   Which process explains this spreading?

   [1 mark]

   • AActive transport
   • BOsmosis
   • CTranspiration
   • DDiffusion

   (b)

   What is the source of energy that causes the purple particles to spread through the water?

   [1 mark]

   • AEnergy released from respiration in the water
   • BEnergy supplied by stirring the beaker
   • CKinetic energy from the random movement of particles
   • DLight energy absorbed by the purple particles

   (c)

   Predict and explain how the rate at which the purple colour spreads would change if the water in the beaker were heated, compared with the original room-temperature water.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   In the lungs, oxygen concentration in the air inside the alveoli is higher than in the blood in the surrounding capillaries, while carbon dioxide concentration is higher in the blood than in the alveolar air.

   (a)

   By which process does oxygen move from the alveoli into the blood?

   [1 mark]

   • AActive transport, using energy from respiration
   • BDiffusion, down its concentration gradient
   • COsmosis, through a partially permeable membrane
   • DDiffusion, against its concentration gradient

   (b)

   Which feature of the alveoli and surrounding capillaries most increases the rate of gas diffusion between them?

   [1 mark]

   • AA thick, impermeable wall
   • BA large surface area and short diffusion distance
   • CA very small surface area
   • DA high concentration of glucose in the blood

   (c)

   Explain why carbon dioxide diffuses out of the blood into the alveolar air, rather than in the opposite direction.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A student sets up an experiment by placing a small cube and a large cube of agar jelly, both dyed with an indicator that changes colour when a chemical diffuses in, into the same beaker of the chemical solution. After 10 minutes, the small cube has changed colour throughout, while the large cube has only changed colour near its surface.

   (a)

   State three factors, other than temperature, that affect the rate of diffusion, and explain which one this experiment demonstrates.

   [3 marks]

   (b)

   Explain the importance of diffusion of both gases and solutes in living organisms, giving one named example of each.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A researcher investigates the rate of diffusion of a dye through cubes of gelatine of different sizes, kept at different temperatures. She finds that diffusion is fastest in small cubes kept at a higher temperature, and slowest in large cubes kept at a lower temperature.

   (a)

   Explain, in terms of particle behaviour, how each of surface area, temperature and concentration gradient affects the rate of diffusion.

   [6 marks]

   (b)

   The researcher then repeats the experiment using a much larger cube of gelatine, at room temperature, and observes that after several hours the centre of the cube still has not changed colour. Explain why living cells and organisms rely on features such as thin surfaces and small size, rather than relying on diffusion alone over large distances, and explain the consequence for a large organism if it relied solely on diffusion to supply oxygen to all its cells.

   [6 marks]

   Total for question 4: 12 marks

End of questions