1. 1
   A student opens a bottle of perfume in the corner of a warm classroom. Within a few minutes, classmates on the other side of the room can smell it, even though there is no draught or air movement in the room.

   (a)

   Which process is responsible for the perfume particles spreading across the classroom and reaching the students on the far side of the room?

   [1 mark]

   • AOsmosis
   • BDiffusion
   • CActive transport
   • DVentilation

   (b)

   Which change would increase the rate at which the perfume particles spread across the room?

   [1 mark]

   • AIncreasing the distance across the room
   • BReducing the concentration of perfume released
   • CIncreasing the temperature of the room
   • DClosing the bottle of perfume sooner

   (c)

   Define diffusion, and state one factor, other than temperature, that affects the rate of diffusion of the perfume particles.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A nurse places a sample of red blood cells into a test tube of pure distilled water and observes them under a microscope. A second sample of red blood cells, from the same patient, is placed into a test tube of a very concentrated salt solution.

   (a)

   What happens to the red blood cells placed into the pure distilled water?

   [1 mark]

   • AThey become crenated (shrink)
   • BThey become plasmolysed
   • CThey remain unchanged
   • DThey become lysed (burst)

   (b)

   What happens to the red blood cells placed into the concentrated salt solution?

   [1 mark]

   • AThey become crenated (shrink)
   • BThey become lysed (burst)
   • CThey become turgid
   • DThey remain exactly the same size

   (c)

   Define osmosis, and use this definition to explain why water moved out of the red blood cells placed in the concentrated salt solution.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A farmer's soil has a much lower concentration of nitrate ions than the concentration found inside the root hair cells of the crop plants growing in it. Despite this, the plants are still able to absorb nitrate ions from the soil into their root hair cells.

   (a)

   Explain how the root hair cells are able to absorb nitrate ions from the soil, even though the soil has a lower concentration of nitrate ions than the inside of the root hair cells.

   [3 marks]

   (b)

   Explain why the plants cannot rely on diffusion to absorb the nitrate ions from the soil, and describe one other example in the human body where a substance is absorbed by the same process used by the root hair cells.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   Since the nineteenth century, scientists have used simple experiments, such as placing potato chips of equal mass into salt solutions of different concentrations, to investigate the movement of water into and out of plant cells.

   (a)

   Describe osmosis and explain its effects on plant cells (turgid, flaccid, plasmolysed) and on animal cells (crenated, lysed).

   [6 marks]

   (b)

   Describe diffusion and the factors that affect its rate, and describe active transport, including one named example.

   [6 marks]

   Total for question 4: 12 marks

End of questions