Aerobic respiration overviewEdexcel A-Level Biology B: Subtopic test

1. 1
   A hummingbird hovers in front of a flower, beating its wings about 50 times each second. Its flight muscle cells contain very large numbers of mitochondria, and the bird feeds on nectar that is rich in sugar.

   (a)

   Which statement about the role of ATP in the hummingbird's muscle cells is correct?

   [1 mark]

   • AATP is a long-term energy store that holds the energy from the nectar for several days
   • BATP carries hydrogen to the mitochondria
   • CHydrolysis of ATP to ADP and phosphate releases energy that is used to drive metabolic reactions
   • DATP is made only in mitochondria

   (b)

   Which stage of aerobic respiration takes place in the cytoplasm of the muscle cells?

   [1 mark]

   • AGlycolysis
   • BThe link reaction
   • CThe Krebs cycle
   • DOxidative phosphorylation

   (c)

   Explain why the flight muscle cells contain very large numbers of mitochondria.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A student places 50 germinating pea seeds in an insulated flask in a dark cupboard and records the temperature each day. A second, identical flask contains boiled peas that cannot respire. After three days the temperature in the first flask has risen from 20.0 °C to 26.5 °C, while the second flask stays at 20.0 °C.

   (a)

   Which statement best explains the rise in temperature in the first flask?

   [1 mark]

   • ARespiration is an endothermic process that takes in heat from the surroundings
   • BThe seeds are photosynthesising in the dark, which releases heat
   • CThe seeds absorb heat from the insulated flask
   • DSome of the energy released in respiration is transferred as heat rather than being captured in ATP

   (b)

   Which equation summarises aerobic respiration of glucose in the germinating seeds?

   [1 mark]

   • AC₆H₁₂O₆ → 2C₃H₆O₃
   • BC₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O
   • CC₆H₁₂O₆ + 6O₂ → 6CO₂ + 12H₂O
   • D6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂

   (c)

   Explain why the temperature in the first flask rose, using ideas about the transfer of energy in respiration.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A researcher breaks open liver cells and separates the contents into two fractions: the cytoplasm, and the mitochondria. She sets up two tubes in aerated solution. Tube 1 contains only the cytoplasm fraction, glucose, ADP, phosphate and NAD. Tube 2 contains only the mitochondria fraction, pyruvate, ADP, phosphate and NAD.

   (a)

   Predict and explain what products will be formed in tube 1 after incubation.

   [3 marks]

   (b)

   Describe the stages in tube 2 that convert pyruvate into ATP, stating where in the mitochondria each stage takes place.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A marathon runner's leg muscle fibres contain many more mitochondria than the epidermal cells of her skin. During a race her muscle fibres use ATP at a very high rate, and her body temperature rises from 37.0 °C to 39.0 °C.

   (a)

   Describe the four stages of aerobic respiration, stating where each takes place and the main products of each.

   [6 marks]

   (b)

   Explain how aerobic respiration in the muscle fibres supplies the energy for contraction, and why the runner's body temperature rises during the race.

   [6 marks]

   Total for question 4: 12 marks

End of questions