1. 1
   A student places 5.0 g of germinating peas in a sealed respirometer tube at 25 °C, together with potassium hydroxide solution, which absorbs carbon dioxide. The tube is connected to a capillary tube with a cross-sectional area of 0.8 mm², containing a drop of coloured liquid. Over 10 minutes the drop moves 36 mm towards the peas. An identical tube containing glass beads instead of peas shows no movement.

   (a)

   What is the purpose of the potassium hydroxide in the respirometer?

   [1 mark]

   • AIt absorbs carbon dioxide, so the movement of the drop is caused by oxygen uptake
   • BIt supplies oxygen to the peas
   • CIt keeps the temperature constant
   • DIt provides the substrate for respiration

   (b)

   What is the rate of oxygen uptake by the peas in mm³ g⁻¹ min⁻¹?

   [1 mark]

   • A2.9
   • B0.58
   • C5.8
   • D7.2

   (c)

   Distinguish between cell respiration and gas exchange, with reference to this experiment.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   At any moment an adult human contains only about 250 g of ATP (adenosine triphosphate), which would supply a working muscle for only a few seconds. Yet the same person hydrolyses roughly 50 kg of ATP to ADP and phosphate each day. Cells use this ATP for processes such as pumping ions across membranes, building proteins and moving chromosomes during cell division.

   (a)

   Which describes the structure of ATP?

   [1 mark]

   • AA nucleotide with adenine, ribose and two phosphate groups
   • BA nucleotide with adenine, deoxyribose and three phosphate groups
   • CAn amino acid with three phosphate groups
   • DA nucleotide with adenine, ribose and three phosphate groups

   (b)

   Which process in cells does not directly use energy from ATP?

   [1 mark]

   • ASynthesis of proteins from amino acids
   • BActive transport of sodium ions out of a cell
   • CDiffusion of oxygen into mitochondria
   • DMovement of chromosomes during mitosis

   (c)

   Deduce what these figures show about the way ATP supplies energy in cells.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A trained athlete runs a 400 m race in 48 seconds. Her blood lactate concentration is 1 mmol dm⁻³ at rest, 14 mmol dm⁻³ two minutes after the race, and 3 mmol dm⁻³ after 30 minutes of rest. During the race her rate of oxygen uptake rises to its maximum within about 30 seconds, but her muscles' demand for ATP is higher than aerobic respiration alone can supply. Aerobic respiration yields about 15 times as much ATP per glucose molecule as anaerobic respiration.

   (a)

   Explain the rise in blood lactate during the race.

   [3 marks]

   (b)

   Discuss the advantages and disadvantages to the athlete of using anaerobic respiration during the race.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A class investigates the effect of temperature on the rate of cell respiration in woodlice using a simple respirometer containing soda lime to absorb carbon dioxide. Each tube holds ten woodlice of known total mass and is placed in a water bath for 5 minutes before readings begin. The mean rates of oxygen uptake from three tubes at each temperature were 0.12 mm³ g⁻¹ min⁻¹ at 10 °C, 0.25 mm³ g⁻¹ min⁻¹ at 20 °C and 0.46 mm³ g⁻¹ min⁻¹ at 30 °C. The woodlice were active and moving around the tubes during the readings.

   (a)

   Using the data, explain the effect of temperature on the rate of cell respiration in woodlice.

   [6 marks]

   (b)

   Evaluate the method used in this investigation and suggest improvements.

   [6 marks]

   Total for question 4: 12 marks

End of questions