Key Area 1.8: Essay Questions

Question 1

Give an account of lactic acid metabolism in muscle cells

Answer 1

• during exercise muscles do not have enough oxygen for aerobic respiration
• pyruvate is converted to lactic acid
• transfer of hydrogen from NADH
• regenerates NAD needed to maintain ATP production by glycolysis
• lactic acid builds up causing fatigue and an oxygen debt
• lactic acid is converted back into pyruvate

Question 2

Give an account of skeletal muscles under the following headings:

a) Slow twitch muscle fibres
b) Fast twitch muscle fibres

Answer 2

a) - slow twitch muscle fibres contract slowly but maintain contractions for a longer period of time
- they rely on aerobic respiration
- they have many mitochondria/ a large blood supply/ high conc of myoglobin
- their main storage fuel is fats
- good for endurance activities eg marathon running
b) - fast twitch muscles fibres contract quickly but cannot maintain contractions for a long period of time
- they generate ATP through glycolysis
- they have few mitochondria and a low blood supply
- their main fuel sources are glycogen and creatine phosphate
- good for short bursts of intense activity eg sprinting