Oxidative phosphorylationEdexcel A-Level Biology A: Subtopic test

1. 1
   A student is revising the final stage of aerobic respiration. This stage takes place on the inner membrane of the mitochondrion, where reduced NAD and reduced FAD from the earlier stages deliver hydrogen to a series of electron carriers called the electron transport chain.

   (a)

   What is the final electron acceptor in the electron transport chain?

   [1 mark]

   • ANAD
   • BCarbon dioxide
   • COxygen
   • DPyruvate

   (b)

   In which direction are protons pumped by the electron transport chain?

   [1 mark]

   • AFrom the matrix into the space between the inner and outer membranes
   • BFrom the space between the membranes into the matrix
   • CFrom the cytoplasm into the matrix
   • DFrom the matrix into the cytoplasm

   (c)

   Explain why the Krebs cycle stops when no oxygen is available, even though oxygen is not used in the cycle.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A researcher suspends intact mitochondria in a solution containing oxygen, ADP and phosphate, and monitors the pH in the space between the inner and outer mitochondrial membranes. When reduced NAD is added, the pH of this space falls and ATP is made. When cyanide is then added, the pH rises again and ATP production stops.

   (a)

   Why does the pH of the intermembrane space fall when reduced NAD is added?

   [1 mark]

   • ACarbon dioxide dissolves in the intermembrane space
   • BLactate accumulates in the intermembrane space
   • CATP is hydrolysed in the intermembrane space
   • DProtons are pumped into the intermembrane space by the electron transport chain

   (b)

   Which statement best explains why ATP production stops when cyanide is added?

   [1 mark]

   • ACyanide prevents glucose entering glycolysis
   • BElectrons cannot be passed to oxygen, so the chain stops and the proton gradient is lost
   • CCyanide makes the inner membrane permeable to ADP
   • DThe proton gradient becomes steeper so ATP synthase stops

   (c)

   Describe how ATP is made when protons move through ATP synthase.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   The inner membrane of a mitochondrion is folded into cristae. It is almost impermeable to protons (hydrogen ions) and contains electron carriers arranged in sequence, together with many molecules of the enzyme ATP synthase. The outer membrane is permeable to small molecules.

   (a)

   Explain how the electron transport chain creates a proton gradient across the inner mitochondrial membrane.

   [3 marks]

   (b)

   Explain how the structure of the inner mitochondrial membrane adapts it for oxidative phosphorylation.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A toxicologist is investigating a patient who has swallowed cyanide. Cyanide inhibits the enzyme that transfers electrons from the last carrier of the electron transport chain to oxygen. The patient breathes rapidly, has a high blood lactate concentration and low cellular ATP, but the oxygen concentration of the patient's blood remains high.

   (a)

   Explain why the cyanide-poisoned patient has low cellular ATP and a high blood lactate concentration, although the blood oxygen concentration is high.

   [6 marks]

   (b)

   Explain how oxidative phosphorylation in a healthy person uses reduced NAD to make ATP, and the role of oxygen.

   [6 marks]

   Total for question 4: 12 marks

End of questions