O-LevelBiologyCoordination & Response5090/21 · Oct/Nov 2021 · Q314 Marks

A man is cooking in a hot kitchen and sweat is being released by sweat glands in his skin. (a) (i) Explain the term homeostasis with reference to sweating. (ii) Explain how receptors and blood vessels in the man's skin are also involved in homeostasis when he is in the hot kitchen. (b) Sweat contains very small quantities of the waste product urea. State the name of the organ where most urea is made in the body. (c) The table shows the concentrations of some chemicals found in the sweat, urine and blood plasma of a healthy human. chemical | concentration of chemical /mmol per dm³ | sweat | urine | blood plasma --- | --- | --- | --- urea | 22 | 393 | 6 sodium | 66 | 110 | 141 chloride | 59 | 103 | 99

(a)(i)Explain the term homeostasis with reference to sweating.[2]
(a)(ii)Explain how receptors and blood vessels in the man's skin are also involved in homeostasis when he is in the hot kitchen.[4]
(b)Sweat contains very small quantities of the waste product urea. State the name of the organ where most urea is made in the body.[1]
(c)(i)Use the data in the table to compare the chemical composition of urine and blood plasma.[4]
(c)(ii)A patient has kidney disease and is about to start dialysis treatment. Suggest and explain the concentration of urea in the sweat of the patient compared to that of a person who does not have kidney disease.[3]

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2021). The mark or mark type is shown in brackets.

[1] any two from: (homeostasis is) the maintenance of a constant ;
[1] internal environment / temperature ;
[1] return to norm / return to set-point / negative feedback ;
[1] evaporation of sweat removes heat / thermal energy / cools / decreases temperature;
[1] any four from: receptors + detection of temperature ;
[1] impulse to brain / CNS ;
[1] vasodilation ;
[1] arterioles / blood vessels widen ;
[1] increase in blood + near skin surface;
[1] greater + loss of heat / thermal energy ;
[1] by radiation;
[1] liver;
[1] any four from: less urea in blood plasma ;
[1] more sodium in blood plasma ;
[1] less chloride in blood plasma ;
[1] comparative data quote with units ;
[1] data manipulation, e.g. 50 × higher urea in urine than blood plasma ;
[1] high(er) / over 22 (in patient);
[1] reduced filtration / reduced removal of urea (from kidney);
[1] reference to blood plasma ;

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