The diagram shows a simplified human muscle cell during a cycling race. The cyclist is climbing a hill, so the muscle needs energy at a high rate. Blood ves...
Question 1 Report
The diagram shows a simplified human muscle cell during a cycling race. The cyclist is climbing a hill, so the muscle needs energy at a high rate. Blood vessels deliver glucose and oxygen to the cell. Some of the glucose is broken down aerobically, but the oxygen supply does not meet all of the demand. The cyclist continues to breathe heavily after reaching the top of the hill.
(a) Name the process that releases energy from glucose using oxygen in this cell. [2]
(b) Describe the word equation for aerobic respiration. [3]
(c) Explain why lactic acid is produced in the cyclist's muscle cells during the hill climb. [4]
(d) State what happens to the lactic acid after exercise has ended. [2]
(e) Explain why energy released by respiration is needed by the cyclist's muscle cells. [3]
Answer Details
(a) The process is aerobic respiration, respiration in muscle cells using oxygen. [2 marks]
(b) The word equation is: \[\text{glucose}+\text{oxygen}\rightarrow\text{carbon dioxide}+\text{water}\] Energy is released in this process. [3 marks]
(c) Climbing requires muscle energy at a high rate. The blood does not deliver enough oxygen to meet this demand, so some glucose is broken down by anaerobic respiration. Anaerobic respiration in muscles produces lactic acid. [4 marks]
(d) After exercise, lactic acid is carried in the blood to the liver, where it is broken down or oxidised when oxygen is available. [2 marks]
(e) Energy released by respiration is needed for muscle contraction and therefore cycling or movement of body parts. It can also be used for active transport to maintain ion gradients, and for building or repairing cell structures. Any three of these uses gain credit. [3 marks]
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