Fig. 1 shows part of a control system used by a researcher studying blood glucose in a healthy adult. The adult cycles for 20 minutes before breakfast. Exer...
Question 1 Report
Fig. 1 shows part of a control system used by a researcher studying blood glucose in a healthy adult. The adult cycles for 20 minutes before breakfast. Exercise causes muscle cells to take up glucose from the blood for respiration. The glucose concentration starts to fall below its normal level. Receptors and the pancreas respond by releasing a hormone. This hormone acts mainly on the liver. The liver changes stored glycogen into glucose and releases glucose into the blood. The response is switched off as the concentration returns to normal. This is negative feedback because the response opposes the original change. The diagram uses boxes to show the order of events.
(a) Name the hormone released by the pancreas in this situation. [1]
(b) Use Fig. 1 to describe the action of this hormone on liver cells. [2]
(c) Suggest why blood glucose concentration can fall during exercise. [2]
(d) Describe why this feedback response stops when the normal concentration is reached. [2]
(e) What molecule is stored in liver cells before it is changed into glucose? [1]
(f) Which body cells need the glucose released into the blood during continued exercise? [1]
Answer Details
(a) The hormone is glucagon. [1 mark]
(b) Glucagon causes liver cells to break down glycogen and release glucose into the blood. [2 marks]
(c) During exercise, muscle cells take up glucose from the blood. They use it in respiration to release energy for contraction, so blood glucose can fall. [2 marks]
(d) The original low glucose concentration has been corrected when the normal level is reached. Continuing to release glucose would make the concentration too high, so negative feedback switches off the response. [2 marks]
(e) The stored molecule is glycogen. [1 mark]
(f) The released glucose is needed by muscle cells during continued exercise. [1 mark]
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