1. 1
   Scientists measure the concentration of nitrate ions inside root hair cells of a plant and find it is much higher than the concentration of nitrate ions in the surrounding soil water. Despite this, the root hair cells continue to absorb more nitrate ions from the soil.

   (a)

   By which process are these ions most likely being absorbed?

   [1 mark]

   • ADiffusion
   • BOsmosis
   • CActive transport
   • DTranspiration

   (b)

   Which structure in the root hair cell membrane is responsible for moving the nitrate ions into the cell against their concentration gradient?

   [1 mark]

   • ARibosomes
   • BProtein carriers
   • CChloroplasts
   • DA cellulose cell wall

   (c)

   Explain why root hair cells contain unusually large numbers of mitochondria.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   Cells lining the small intestine continue to absorb glucose from the gut even after the glucose concentration inside these cells has become higher than in the gut contents.

   (a)

   Which process is responsible for this continued absorption of glucose?

   [1 mark]

   • AActive transport
   • BDiffusion
   • COsmosis
   • DFiltration

   (b)

   What would happen to the rate of glucose absorption by these intestinal cells if a poison that stops respiration were applied to them?

   [1 mark]

   • AThe rate of absorption would increase
   • BThe rate of absorption would be unaffected
   • CGlucose would instead move out of the cells by active transport
   • DThe rate of absorption would decrease or stop

   (c)

   Explain why glucose absorption by intestinal cells cannot be explained by diffusion alone once the glucose concentration inside the cells is higher than in the gut.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A student compares diffusion and active transport as two ways that substances move across cell membranes, using the example of root hair cells absorbing mineral ions from dilute soil water.

   (a)

   State three differences between diffusion and active transport.

   [3 marks]

   (b)

   Explain the importance of active transport for root hair cells absorbing mineral ions from dilute soil water, and describe what would happen to plant growth if active transport in root hair cells was not possible.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A plant is grown in soil that is very deficient in nitrate ions. Scientists find that the plant's root hair cells still manage to accumulate nitrate ions at a much higher concentration than in the surrounding soil, but that the roots use unusually large amounts of oxygen while doing so.

   (a)

   Explain, in terms of active transport, protein carriers and respiration, how the root hair cells achieve this accumulation of nitrate ions, and explain why the roots use large amounts of oxygen.

   [6 marks]

   (b)

   The scientists then reduce the oxygen concentration around the roots of the same plant, while keeping the soil nitrate concentration the same. Explain how you would expect the rate of nitrate ion uptake by the root hair cells to change, and explain the biological reasoning behind your prediction.

   [6 marks]

   Total for question 4: 12 marks

End of questions