A-LevelBiologyHomeostasis9700/41 · May/June 2025 · Q711 Marks

Insulin is an example of a cell-signalling molecule of the endocrine system.

(a)Outline why insulin can be described as an example of a cell-signalling molecule of the endocrine system.[4]
(b)(i)Researchers compared the effect of two types of meal on the mean blood glucose concentration and the mean blood insulin concentration of twelve volunteers. The measurements were made for three hours after the meal. Meal A contained 55% carbohydrate, 27% fat and 18% protein. Meal B contained 3% carbohydrate, 90% fat and 7% protein. Fig. 7.1 shows the results. [Figure 7.1] With reference to Fig. 7.1, explain how negative feedback operates to control mean blood glucose concentration in the volunteers who ate meal A.[4]
(b)(ii)Suggest explanations for the changes in mean blood glucose concentration of the volunteers who ate meal B.[3]

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Mark scheme

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

[4] (a) any four from: 1 insulin / it, is a hormone ; 2 (described) stimulus causes insulin to be secreted from (named) endocrine, gland / tissue / cells ; 3 insulin travels in blood; 4 binds to receptors on (named) target cells ; 5 to cause (described) response ; 6 AVP;
[4] (b)(i) any four from: 1 at 21 min, blood glucose concentration / it, rises to 110 mg 100 cm-3 ; 2 (high/increase in, blood glucose concentration) detected by pancreas / causes response in pancreas ; 3 insulin rises to 500 pmol dm-3 ; 4 (insulin) increase GLUT proteins in membrane / increases glucose uptake into cells / increases cell permeability to glucose or (insulin) increases rate of respiration of glucose ; 5 (insulin) causes / stimulates, glycogenesis / lipogenesis ; 6 (mean) blood glucose concentration / it, falls, to normal / within normal range / below starting point / to set point;
[3] (b)(ii) any three from: 1 blood glucose concentration falls as glucose is respired ; 2 blood glucose concentration falls below, set point/normal ; 3 insulin, secretion / release, stops ; 4 glucagon (secreted / released / rises); 5 glycogen, (in cells) converted to glucose or glycogenolysis ; 6 (stored) protein / fat, converted to glucose or gluconeogenesis or (stored) protein / fat, used for respiration;

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