A-LevelBiologyHomeostasis9700/43 · May/June 2022 · Q1010 Marks

(a) Insulin has an important role in the maintenance of blood glucose concentration. An investigation measured how blood glucose concentration and blood insulin concentration changed after a glucose-rich meal had been eaten. The results are shown in [Figure 10.1].

(a)(i)Describe and explain how the results shown in [Figure 10.1] indicate a relationship between blood glucose concentration and blood insulin concentration after the consumption of a glucose-rich meal.[3]
(a)(ii)Suggest and explain how the results shown in [Figure 10.1] would change if the meal was mostly starch rather than glucose.[3]
(b)Glucagon is synthesised by cells in the pancreas known as alpha (α) cells. Glucagon binds to G-protein-coupled receptors in the cell surface membrane of liver cells. This results in the activation of G-proteins. Outline the sequence of events occurring within the cell after the activation of G-proteins that helps to restore the blood glucose concentration to its set point.[4]

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Mark scheme

Marking points from the official mark scheme (May/June 2022). The mark or mark type is shown in brackets.

any three from: 1 as the, blood glucose / glucose concentration, increases the, blood insulin / insulin concentration, increases ; A positive correlation
2 data quote with unit;
3 increase in, blood glucose / glucose concentration, causes release of insulin (from pancreas); ora
4 insulin stimulates the conversion of glucose to glycogen / glycogenesis or insulin increases permeability (of liver / muscle) cells to glucose / AW;
5 insulin causes, blood glucose / glucose concentration, to return back to set point ;
6 ref. to negative feedback;
any three from: max 2 if only glucose or insulin curve mentioned
1 ref. to delay before both graphs increase / AW ;
2 peaks for both would be lower ;
3 both curves would take longer to decrease ;
4 time is needed for starch to be, broken down / converted (to glucose);
5 to glucose ;
any four from: 1 ref. to adenylyl cyclase;
2 formation of, cyclic AMP / cAMP;
3 cAMP acts as a second messenger ;
4 activation of (protein) kinase ;
5 enzyme cascade ;
6 amplification of signal;
7 glycogenolysis / gluconeogenesis / described ;
8 glucose released into blood ;

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