A-LevelBiologyHomeostasis9700/41 · Oct/Nov 2017 · Q812 Marks

(a) Homeostasis in mammals involves negative feedback mechanisms. Outline how a negative feedback mechanism works. (b) [Figure 8.1] is a diagram summarising the role of the nervous and endocrine systems in the control of blood glucose concentration. With reference to Fig. 8.1, describe the role of the nervous system in the control of blood glucose concentration. (c) If the core temperature of the human body falls, the hypothalamus sends impulses to activate several physiological responses, some of which are listed below. For each one, state how it would help to bring the core temperature back to normal. vasoconstriction shivering increasing secretion of adrenaline

(a)Outline how a negative feedback mechanism works.[4]
(b)With reference to Fig. 8.1, describe the role of the nervous system in the control of blood glucose concentration.[4]
(c)If the core temperature of the human body falls, the hypothalamus sends impulses to activate several physiological responses, some of which are listed below. For each one, state how it would help to bring the core temperature back to normal. vasoconstriction shivering increasing secretion of adrenaline[4]

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Mark scheme

Marking points from the official mark scheme (Oct/Nov 2017). The mark or mark type is shown in brackets.

[4] 8(a) four from: 1 change in factor away from, the norm / set-point ; 2 detected / sensed by, receptor ; 3 hormone released or (nerve) impulse sent ; 4 (hormone / impulse) reaches, target organ / effector ; 5 (effector) performs corrective action ; 6 (factor) returns to, norm / set-point ;
[4] 8(b) four from: 1 hypothalamus detects change in blood glucose concentration ; 2 autonomic / motor / nerve, impulses ; 3 (so) β cells secrete insulin when blood glucose increases ; 4 (so) α cells secrete glucagon when blood glucose decreases ; 5 (so) adrenal gland secretes adrenaline either when blood glucose decreases or due to fear / shock / excitement / stress ; 6 nervous control supplements, endocrine control / control by pancreas ;
[4] 8(c) four from: vasoconstriction 1 arterioles in skin get narrow(er) ; 2 less blood flow through (skin / surface) capillaries ; 3 (so) less heat lost (to surroundings) ; shivering 4 muscle contraction ; 5 releases / provides / gives, heat / thermal energy ; increasing secretion of adrenaline 6 increases, rate of respiration / metabolic rate ; 7 more heat, released / provided / given (by respiration) ;

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