Oxidative phosphorylation and respiratory quotientEdexcel International A Level Biology: Subtopic test

1. 1
   Skeletal muscle cells make most of their ATP in mitochondria by oxidative phosphorylation. Electron micrographs show that the mitochondria of muscle cells have many more cristae than those of cells that are less active.

   (a)

   Where in a mitochondrion is the electron transport chain found?

   [1 mark]

   • AIn the matrix
   • BIn the inner membrane
   • CIn the outer membrane
   • DIn the cytoplasm around the mitochondrion

   (b)

   What is the final acceptor of electrons at the end of the electron transport chain?

   [1 mark]

   • AOxygen
   • BNAD
   • CCarbon dioxide
   • DADP

   (c)

   Explain why the mitochondria in muscle cells have many cristae.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A volunteer who had not eaten for three days breathed through a respirometer. The volunteer used 250 cm³ of oxygen and produced 190 cm³ of carbon dioxide each minute at rest.

   (a)

   What is the respiratory quotient of the volunteer?

   [1 mark]

   • A1.32
   • B0.24
   • C0.76
   • D1.00

   (b)

   Which conclusion about the respiratory substrate is best supported by the result?

   [1 mark]

   • ACarbohydrate only is being respired
   • BThe volunteer is respiring anaerobically
   • CProtein only is being respired
   • DA large proportion of the substrate is lipid

   (c)

   Explain why the respiratory quotient for lipids is lower than that for carbohydrates.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A student investigates the respiration of 5 g of germinating pea seeds at 20 °C in two simple respirometers. In tube A the carbon dioxide is absorbed by potassium hydroxide solution. Tube B has no potassium hydroxide solution. The cross-sectional area of the capillary tube is 0.80 mm². In 10 minutes the coloured liquid in tube A moved 30 mm towards the seeds, and in tube B it moved 6 mm towards the seeds.

   (a)

   Explain what the movement of the liquid in tube A measures and calculate the rate of this process in mm³ per minute.

   [3 marks]

   (b)

   Use the results from both tubes to calculate the respiratory quotient of the seeds. Suggest what your answer shows about the respiratory substrate.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   Researchers isolated intact mitochondria from rat liver and suspended them in a buffered solution containing pyruvate and oxygen. They measured the concentration of oxygen and the amount of ATP produced. They then added an uncoupling agent, a lipid-soluble molecule that carries hydrogen ions across the inner mitochondrial membrane, making the membrane leaky to hydrogen ions.

   (a)

   Describe how ATP is made by oxidative phosphorylation in the mitochondria before the uncoupling agent is added.

   [6 marks]

   (b)

   Explain the effect of the uncoupling agent on the uptake of oxygen and on the production of ATP, and suggest why the mitochondria become warmer.

   [6 marks]

   Total for question 4: 12 marks

End of questions