Describe the advantage of the Bohr effect during intense exercise.

A cyclist completed a fitness test on an exercise bike. The intensity of the exercise was increased every 10 seconds. The test finished when he was unable to cycle any further. The partial pressure of oxygen (pO2) and of carbon dioxide (pCO2) in air breathed out was measured.

Figure 3 shows the results of the cyclist's fitness test.

Ventilatory threshold (VT) is a measure of the point when anaerobic respiration increases because aerobic respiration alone can no longer maintain muscle contraction.

VT can be identified as the first point when there is an increase in pO2 breathed out, without an equivalent increase in pCO2 breathed out.

Use Figure 3 to determine the time after the exercise started when the cyclist reached VT.

Calculate the ratio of pO2 to pCO2 in breathed-out air at this time.

Show your working.

Time when the cyclist reached VT = ______________ min

Ratio of pO2 to pCO2 at VT = ______________:1

An increase in the intensity of exercise produces an increase in the volume of carbon dioxide produced.

However, Figure 3 shows that the pCO2 in air breathed out did not show a large increase during the exercise.

Suggest one physiological change that would cause this result. Explain how the physiological change would allow for the removal of the increase in the volume of carbon dioxide produced.

Physiological change ______________

Explanation ______________

When muscle fibres have very low concentrations of ATP, they may get ATP in the following ways.

• AMPK (an enzyme) oxidises fatty acids.

• Phosphocreatine donates phosphate to ADP in anaerobic conditions.

Figure 4 shows how these chemicals work.

At more than 80% of maximum muscle effort, ATP can only be made for a limited time.

Use Figure 4 to suggest one reason why.

Tick (✓) the correct box.

☐ ATP cannot move into muscle fibres at a fast-enough rate.

☐ Muscle fibres have a limited amount of phosphocreatine.

☐ Muscle fibres produce too much lactate.

☐ Muscle fibres quickly run out of ADP.

GW1516 is a performance-enhancing drug. GW1516 activates AMPK and develops slow muscle fibres at rest.

Use Figure 4 to justify why professional athletes are not allowed to take GW1516.

Do not include details of chemiosmotic theory in your answer.

EPO is another performance-enhancing drug. It can increase the haematocrit (the percentage of red blood cells in blood).

A heart attack is caused by a lack of glucose and oxygen being delivered to cardiac muscle via the coronary arteries. The overuse of EPO can increase the risk of a heart attack.

Suggest how.

The normal haematocrit for human males is 47(±5)%. For professional male cyclists, the maximum haematocrit allowed is 50%.

A student suggested that professional male cyclists should be allowed to use EPO until their haematocrit is 50%.

Give two reasons why this suggestion is not valid.

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