1. 1
   A baker mixed yeast with sugar and warm water and sealed the mixture in an airtight container with no added oxygen. After some time, the dough was found to have risen noticeably and smelled faintly of alcohol.

   (a)

   Which process in the yeast produced these results?

   [1 mark]

   • AAnaerobic respiration
   • BAerobic respiration
   • CPhotosynthesis
   • DActive transport

   (b)

   Which gas produced by the yeast caused the dough to rise?

   [1 mark]

   • AOxygen
   • BCarbon dioxide
   • CNitrogen
   • DHydrogen

   (c)

   Write the word equation for anaerobic respiration in yeast, and explain why this process releases much less energy per glucose molecule than aerobic respiration would.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A weightlifter performed a single very heavy lift, contracting their leg and back muscles with maximum effort for only a few seconds. Their muscles were unable to obtain enough oxygen quickly enough from the blood to meet this sudden, intense demand for energy.

   (a)

   Which type of respiration occurred in these muscles to help supply the extra energy needed?

   [1 mark]

   • AAerobic respiration only, since the body always has enough oxygen
   • BAnaerobic respiration, producing alcohol and carbon dioxide
   • CAnaerobic respiration, producing lactic acid
   • DPhotosynthesis, producing glucose and oxygen

   (b)

   Write the word equation for anaerobic respiration occurring in the weightlifter's muscles during this lift.

   [1 mark]

   • ACarbon dioxide + water → glucose + oxygen
   • BGlucose + oxygen → carbon dioxide + water
   • CGlucose → alcohol + carbon dioxide
   • DGlucose → lactic acid

   (c)

   Explain what is meant by an oxygen debt, and describe how the weightlifter's body would begin to repay this oxygen debt immediately after the lift.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   Several minutes after finishing an intense training session, an athlete's muscles still felt fatigued and their breathing and heart rate remained above resting levels, even though they were no longer exercising.

   (a)

   Explain, in terms of lactic acid transport, why the athlete's heart rate stayed high during this recovery period.

   [3 marks]

   (b)

   Explain, in detail, what happens to the lactic acid once it reaches the liver, and describe why the athlete's breathing rate needed to remain deep and fast during this recovery period rather than returning immediately to normal.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A sports scientist compared laboratory data on anaerobic respiration in a flask of fermenting yeast with data collected from an athlete's muscles during a short burst of maximal effort exercise, examining the reactants, products and energy released in each case.

   (a)

   Compare the process of anaerobic respiration in yeast with anaerobic respiration in human muscle, describing the reactants, products and energy release in each, and explaining why organisms use anaerobic respiration despite it releasing less energy than aerobic respiration.

   [6 marks]

   (b)

   The scientist proposed that both yeast fermentation and anaerobic respiration in muscle are ultimately limiting processes that cannot sustain energy release indefinitely. Discuss the factors that would eventually limit anaerobic respiration in each case, and explain why neither process can substitute fully for aerobic respiration over a long period.

   [6 marks]

   Total for question 4: 12 marks

End of questions