1. 1
   A student places 10 g of germinating maize grains in a sealed 250 cm³ chamber fitted with a carbon dioxide sensor at 20 °C. Over 30 minutes the carbon dioxide concentration rises from 400 ppm to 2200 ppm. In a second chamber, 10 g of maize grains that had been boiled and cooled produce no change in carbon dioxide concentration.

   (a)

   What was the mean rate of carbon dioxide production per gram of grains?

   [1 mark]

   • A60 ppm min⁻¹ g⁻¹
   • B6.0 ppm min⁻¹ g⁻¹
   • C180 ppm g⁻¹
   • D7.3 ppm min⁻¹ g⁻¹

   (b)

   What is the purpose of the chamber containing boiled grains?

   [1 mark]

   • ATo show that the increase in carbon dioxide is caused by respiration in living grains
   • BTo provide extra carbon dioxide for the germinating grains
   • CTo keep the temperature of both chambers the same
   • DTo measure the rate of anaerobic respiration

   (c)

   Outline the energy transfers that occur when ATP is used and regenerated in the maize cells.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   In bread-making, yeast (Saccharomyces cerevisiae) is mixed into dough and left in a warm place. The yeast cells quickly use up the oxygen trapped in the dough and then respire anaerobically. The dough rises, and during baking the ethanol produced evaporates. In brewing, yeast is kept in sealed vessels from which carbon dioxide can escape but air cannot enter.

   (a)

   What are the products of anaerobic respiration of glucose in yeast?

   [1 mark]

   • ALactate and carbon dioxide
   • BLactate only
   • CCarbon dioxide and water
   • DEthanol and carbon dioxide

   (b)

   Why is it essential for yeast to convert pyruvate to ethanol when oxygen is absent?

   [1 mark]

   • AIt supplies the acetyl groups for the Krebs cycle
   • BIt produces most of the ATP in anaerobic respiration
   • CIt regenerates NAD from reduced NAD so that glycolysis can continue
   • DIt uses up carbon dioxide produced by glycolysis

   (c)

   Compare anaerobic cell respiration in yeast with anaerobic cell respiration in human muscle.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   Mitochondria were isolated from liver cells and suspended in a buffer containing pyruvate and phosphate. Their oxygen consumption was measured in nmol O₂ per minute per mg of mitochondrial protein. With pyruvate alone, consumption was 20. When ADP was added, it rose to 90 and ATP was produced. Cyanide, which blocks the transfer of electrons from the last carrier of the electron transport chain to oxygen, was then added: consumption fell to 2 and ATP production stopped. In a separate sample with pyruvate and ADP, the compound DNP, which makes the inner mitochondrial membrane permeable to protons, was added: oxygen consumption rose to 110, ATP production stopped and the suspension warmed slightly.

   (a)

   Explain the effect of cyanide on oxygen consumption and ATP production.

   [3 marks]

   (b)

   Using chemiosmosis, explain the results obtained with DNP.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   Bar-tailed godwits (Limosa lapponica) migrate from Alaska to New Zealand, flying about 11 000 km without stopping to feed. Before departure they store so much fat that it makes up over half of their body mass, and during the flight their flight muscles respire mainly fatty acids. Respiring 1 g of lipid releases about 39 kJ of energy, while 1 g of carbohydrate releases about 17 kJ. Carbohydrate stored as glycogen is also held with about 3 g of water per gram of glycogen.

   (a)

   Explain why lipid is a better fuel than carbohydrate for the godwit's flight, and outline how fatty acids are used in cell respiration.

   [6 marks]

   (b)

   Describe what happens to an acetyl group from the time it enters the Krebs cycle until the energy it releases is used to make ATP.

   [6 marks]

   Total for question 4: 12 marks

End of questions