Outline what is meant by homeostasis.

Describe how body temperature is maintained in humans.

Explain the processes occurring in the kidney that contribute to osmoregulation.

maintaining (stable) internal environment/conditions;
within (narrow) limits;
example (e.g. body temperature / blood pH / blood glucose / water / CO₂ concentration);
levels of these variables are monitored (internally);
negative feedback mechanisms / OWTTE; (reject if positive feedback included)
involves hormonal / nervous control;

maintained close to 36.7/37°C/98.6°F ;
heat is transferred/distributed in body by blood;
hypothalamus contains thermoreceptors;
hypothalamus monitors temperature/sends message to effectors/causes response;
(vaso) dilation of skin arterioles warms skin/cools body;
(vaso) constriction of skin arterioles retains body heat;
skin/sweat glands produce sweat to cool the body when overheated;
removal of heat through evaporation of sweat;
shivering generates heat / increased metabolism / hair erection to retain heat;
example of behavioural change to warm/cool the body to thermoregulate;

osmoregulation is maintenance of water balance of blood/tissues;
loop of Henle creates hypertonic conditions in the medulla;
water reabsorbed as filtrate passes through collecting duct;
hypothalamus monitors/controls water balance/content of blood;
controls secretion of ADH by (posterior) pituitary gland;
ADH is released when blood too concentrated/too little water/hypertonic;
ADH makes the collecting duct more permeable to water;
due to more aquaporins;
more water reabsorbed (in response to ADH);
less water in urine/urine more concentrated/urine hypertonic;
no/less ADH when blood too dilute/too much water/hypotonic;
collecting duct less permeable/less water reabsorption/more water in urine;

Answers were variable here with some exemplary accounts but also some very vague ones. Weaker candidates tended to omit the idea that homeostasis is control of the internal environment. Some candidates suggested instead that it involves a person controlling their external environment. There was also some confusion between homeostasis and response to external stimuli such as touching a hot object.

There were some relatively easy marks to be earned here but even so answers ranged from zero to five. A persistent area of confusion is vasoconstriction and dilation. Fewer candidates than at one time now write about blood vessels moving closer to the skin or further away but some still suggest that it is capillaries in the skin that actively constrict or dilate, rather than the arterioles that serve them.

There were some long and detailed answers to this part of the question, although the eight marks could be scored in relatively short answers if they were confined to the processes in the kidney that vary depending on the condition of the blood. There was no need to write about ultrafiltration in the glomerulus or selective reabsorption in the proximal convoluted tubule. Processes occurring in the loop of Henle should have been mentioned, but only so as to explain how they establish hypertonic conditions in the medulla and allow the production of hypertonic urine. The main focus of the answer should have been on how the secretion of ADH is regulated and how this hormone controls the rate of water reabsorption in the collecting duct.