A-LevelBiologyHomeostasis9700/42 · Feb/Mar 2025 · Q611 Marks

[Figure 6.1] outlines part of the control mechanism that regulates blood glucose concentration.

(a)(i)Identify P, Q and R. P Q R[3]
(a)(ii)State the type of homeostatic control mechanism operating in Fig. 6.1.[1]
(b)When the blood glucose concentration decreases below the set point, a hormone is released from the pancreas. Describe how the release of this hormone leads to the blood glucose concentration returning to the set point.[7]

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Mark scheme

Marking points from the official mark scheme (Feb/Mar 2025). The mark or mark type is shown in brackets.

[3] P - insulin; Q - muscle / liver ; R - glycogen ;
[1] negative feedback ;
[7] any seven from: 1 glucagon; 2 binds to receptor on cell surface membrane (of liver cell); 3 G-protein activated; 4 adenyl(yl) cyclase activated ; 5 ATP converted to cAMP ; 6 second messenger ; 7 enzyme cascade / described ; 8 enzymes activated by phosphorylation ; 9 signal amplified ; 10 glycogen broken down into glucose / glycogenolysis ; 11 glucose enters blood ; 12 gluconeogenesis / described ;

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