Oxidative phosphorylationAQA A-Level Biology: Subtopic test

1. 1
   Mitochondria were isolated from heart muscle and the processes taking place at their inner membranes were investigated.

   (a)

   Where in a mitochondrion does oxidative phosphorylation take place?

   [1 mark]

   • AMitochondrial matrix
   • BOuter mitochondrial membrane
   • CInner mitochondrial membrane
   • DSpace between the two membranes

   (b)

   Which enzyme catalyses the synthesis of ATP in oxidative phosphorylation?

   [1 mark]

   • AATP synthase
   • BATP hydrolase
   • CDehydrogenase
   • DCytochrome oxidase

   (c)

   Describe the role of reduced NAD in oxidative phosphorylation.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   In respiring mitochondria the intermembrane space is found to be more acidic than the matrix.

   (a)

   Which statement describes the movement of protons through ATP synthase?

   [1 mark]

   • AFrom the matrix to the intermembrane space, against their gradient
   • BFrom the intermembrane space into the matrix, down their gradient
   • CFrom the cytoplasm into the matrix
   • DFrom the matrix to the cytoplasm

   (b)

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

   [1 mark]

   • ACarbon dioxide
   • BWater
   • COxygen
   • DNAD

   (c)

   Explain why the intermembrane space is more acidic than the matrix in respiring mitochondria.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   Two inhibitors are added, separately, to suspensions of respiring mitochondria that are supplied with reduced NAD and oxygen. Inhibitor X blocks the channel in ATP synthase so that protons cannot pass through it. Inhibitor Y blocks the last carrier of the electron transfer chain so that electrons cannot be passed to oxygen.

   (a)

   Predict the effects of inhibitor X on ATP synthesis, on the proton concentration in the intermembrane space and on oxygen consumption, giving reasons.

   [3 marks]

   (b)

   Explain the effects of inhibitor Y on the proton gradient, on ATP synthesis and on the Krebs cycle.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   Heart muscle cells have many mitochondria with extensively folded inner membranes. A researcher adds a chemical to respiring mitochondria that makes the inner mitochondrial membrane freely permeable to protons, so protons flow back into the matrix without passing through ATP synthase.

   (a)

   Describe how ATP is made by oxidative phosphorylation in mitochondria that have not been treated with the chemical.

   [6 marks]

   (b)

   Predict and explain the effects of the chemical on ATP synthesis, oxygen consumption and the temperature of the mitochondria.

   [6 marks]

   Total for question 4: 12 marks

End of questions