Anaerobic respirationEdexcel A-Level Biology B: Subtopic test

1. 1
   A 400 m sprinter runs a race lasting about 50 seconds. Oxygen cannot be delivered to her leg muscles quickly enough to meet demand, so much of the ATP for the final stretch is made without oxygen.

   (a)

   What is the net yield of ATP from one molecule of glucose when only glycolysis takes place?

   [1 mark]

   • A0
   • B2
   • C4
   • D30

   (b)

   Which compound is converted into lactate in her muscle cells?

   [1 mark]

   • AGlucose
   • BAcetyl coenzyme A
   • CPyruvate
   • DEthanal

   (c)

   Explain why the conversion of pyruvate to lactate allows glycolysis to continue in her muscles.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   Rice plants grown in flooded paddy fields have roots surrounded by waterlogged soil that contains very little oxygen. Root cells of these plants can keep respiring for a time without oxygen.

   (a)

   Which gas is released when pyruvate is converted to ethanal in these root cells?

   [1 mark]

   • AOxygen
   • BHydrogen
   • CNitrogen
   • DCarbon dioxide

   (b)

   What happens to reduced NAD when ethanal is converted into ethanol?

   [1 mark]

   • AIt is reduced to form more ATP
   • BIt is oxidised to NAD as ethanal is reduced
   • CIt is converted to lactate
   • DIt enters the Krebs cycle

   (c)

   State two differences between anaerobic respiration in these root cells and in mammalian muscle cells.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A student used a respirometer to measure the rate of oxygen uptake by 5 g of germinating pea seeds at 20 °C. Carbon dioxide produced was absorbed by potassium hydroxide solution. A coloured liquid droplet in a capillary tube of internal radius 0.50 mm moved 24 mm towards the seeds in 6.0 minutes. A second, control tube contained glass beads with the same volume as the peas.

   (a)

   Calculate the rate of oxygen uptake of the seeds in mm³ min⁻¹. Give your answer to three significant figures and show your working.

   [3 marks]

   (b)

   Explain the function of the potassium hydroxide solution and of the control tube, and explain why the droplet moved towards the seeds.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   During a hill-running session an athlete sprints uphill in repeated bursts. Blood samples taken at the end of each sprint show a rising lactate concentration and a blood pH that falls from 7.4 to 7.0.

   (a)

   Explain how the production of lactate affects muscle contraction, and how the athlete's body deals with the lactate after the session.

   [6 marks]

   (b)

   Evaluate the use of anaerobic respiration rather than aerobic respiration as the main source of ATP for a sprint.

   [6 marks]

   Total for question 4: 12 marks

End of questions