Active transport, vesicles and ATPEdexcel A-Level Biology B: Subtopic test

1. 1
   Root hair cells absorb nitrate ions from soil water. The concentration of nitrate ions inside a root hair cell is often higher than in the soil water. Researchers found that when the cells were treated with cyanide, which stops respiration, nitrate uptake fell sharply.

   (a)

   Which observation is the best evidence that nitrate uptake is by active transport?

   [1 mark]

   • ANitrate ions continue to enter even when their concentration inside the cell is higher than outside
   • BNitrate uptake increases when more channel proteins are present
   • CNitrate uptake is unaffected by cyanide
   • DNitrate ions move in and out of the cell at equal rates

   (b)

   What is the role of ATP in the active transport of nitrate ions?

   [1 mark]

   • AIt is carried across the membrane with the nitrate ions
   • BIt is hydrolysed to ADP and phosphate, releasing energy that changes the shape of the carrier protein
   • CIt forms a channel through the phospholipid bilayer
   • DIt is made when ADP is hydrolysed by the carrier protein

   (c)

   Explain why nitrate uptake falls when the root hair cells are treated with cyanide.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   Cells of the pancreas make digestive enzymes, which are packaged into vesicles and released from the cell. Neutrophils, a type of white blood cell, take in bacteria from the blood plasma and destroy them.

   (a)

   Which process releases the digestive enzymes from the pancreatic cells?

   [1 mark]

   • AFacilitated diffusion through channel proteins
   • BEndocytosis, in which the membrane engulfs the enzymes
   • CSimple diffusion through the phospholipid bilayer
   • DExocytosis, in which vesicles fuse with the cell surface membrane

   (b)

   What happens to the surface area of the cell surface membrane of a pancreatic cell when many vesicles fuse with it?

   [1 mark]

   • AIt decreases, because the cell loses material
   • BIt stays the same, because vesicle membranes are broken down
   • CIt increases, because the membrane of each vesicle becomes part of the cell surface membrane
   • DIt decreases, because the vesicles pinch off from the surface

   (c)

   Describe how a neutrophil takes in a bacterium from the blood plasma.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   ATP is the immediate source of energy for cell processes. A muscle cell holds only a small store of ATP, but during a sprint it uses ATP very quickly and regenerates it from ADP and inorganic phosphate using energy released in respiration.

   (a)

   Describe how ATP provides energy for cell processes and how it is regenerated.

   [3 marks]

   (b)

   Explain why ATP is more suitable as the immediate source of energy for cell processes than glucose.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   Cells from the root of a plant were placed in a solution containing potassium ions. The concentration of potassium ions inside the cells was 10 times higher than in the solution. The rate of potassium uptake was 8.4 units under normal, aerated conditions, 1.5 units when the cells were treated with cyanide (an inhibitor of respiration) and 2.1 units at 4 °C. The cells also take up oxygen and secrete a large protein.

   (a)

   Explain how the data show that potassium ions are taken up by active transport.

   [6 marks]

   (b)

   Explain why oxygen, potassium ions and the large protein must each cross the cell surface membrane by a different method.

   [6 marks]

   Total for question 4: 12 marks

End of questions