1. 1
   A student wrote the word equation for aerobic respiration: glucose + oxygen → carbon dioxide + water, and was asked to identify the balanced chemical equation and the site within the cell where most of this process occurs.

   (a)

   A student wrote the word equation for a type of respiration that requires oxygen: glucose + oxygen → carbon dioxide + water. What type of respiration does this equation represent?

   [1 mark]

   • AAerobic respiration
   • BAnaerobic respiration in muscle
   • CAnaerobic respiration in yeast
   • DPhotosynthesis

   (b)

   Which balanced chemical equation correctly represents aerobic respiration?

   [1 mark]

   • A$C_6H_{12}O_6 \rightarrow 2C_3H_6O_3$
   • B$6CO_2 + 6H_2O \rightarrow C_6H_{12}O_6 + 6O_2$
   • C$C_6H_{12}O_6 \rightarrow 2C_2H_5OH + 2CO_2$
   • D$C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O$

   (c)

   Name the organelle in which most of the reactions of aerobic respiration take place, and explain why cells that are very active, such as muscle cells, tend to contain large numbers of this organelle.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A scientist measured the rate of aerobic respiration in a sample of germinating seeds at a range of increasing temperatures. The rate of respiration increased steadily up to an optimum temperature, then fell sharply as temperature increased further.

   (a)

   What most likely explains the rate falling sharply at higher temperatures?

   [1 mark]

   • AGlucose is destroyed at higher temperatures
   • BOxygen becomes unavailable at higher temperatures
   • CEnzymes controlling respiration become denatured above their optimum temperature
   • DCarbon dioxide production stops completely at higher temperatures

   (b)

   Which statement correctly describes the relationship between enzymes and the rate of respiration shown in this investigation?

   [1 mark]

   • ARespiration does not involve enzymes, so temperature has no real effect on its rate
   • BRespiration is controlled by enzymes, so its rate depends on factors that affect enzyme activity, such as temperature
   • CEnzymes are only involved in anaerobic respiration, not aerobic respiration
   • DEnzymes are destroyed permanently below the optimum temperature

   (c)

   Explain, in terms of enzyme action, why the rate of respiration increased steadily up to the optimum temperature but then fell sharply beyond it.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A student measured the rate of oxygen consumption in a resting person and again during moderate exercise, finding it much higher during exercise. A teacher then asked the class to consider what would happen if the exercise intensity became so great that oxygen supply could no longer keep pace with demand.

   (a)

   Explain why oxygen consumption increases during moderate exercise, in terms of aerobic respiration.

   [3 marks]

   (b)

   Explain what would happen to the rate of energy release in the muscles if exercise intensity increased so much that oxygen supply could no longer keep pace with aerobic respiration alone, and outline the consequence for the muscle cells.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A biology teacher demonstrated aerobic respiration in germinating peas using a respirometer, showing that oxygen was consumed and carbon dioxide was produced as the peas released energy from stored nutrients.

   (a)

   Describe the process of aerobic respiration, including the reactants and products involved and the role of mitochondria, and explain why aerobic respiration releases much more energy per glucose molecule than anaerobic respiration.

   [6 marks]

   (b)

   The teacher then placed a second set of germinating peas in an identical respirometer but sealed inside a container with no oxygen present. Predict and explain what would happen to the rate and type of respiration occurring in these peas, and discuss the long-term consequences for the peas if they were kept without oxygen indefinitely.

   [6 marks]

   Total for question 4: 12 marks

End of questions