Outline what is meant by homeostasis.

Describe how body temperature is maintained in humans.

Explain the need for a ventilation system and the mechanism of ventilation of the lungs in humans.

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;

(cellular) respiration drives the need for gas exchange/absorption of oxygen and removal of CO₂;
gas exchange depends upon a ventilation system;
lungs/alveoli provide surface area for gas exchange (with capillaries/blood);
ventilation system maintains a high concentration of oxygen in the alveoli;
bloodstream links alveoli to cells;
inhalation by contraction of diaphragm;
inhalation occurs with contraction of external intercostals/relaxation of internal intercostals;
(these) increase the volume/reduce the pressure in thorax, pulling air into lungs;
exhalation caused by relaxation of the diaphragm;
exhalation occurs with relaxation of external intercostals/contraction of internal intercostals;
(these) decrease volume/increase pressure in the thorax, forcing air out of lungs;

On question 7, candidates tended to score either high or low for the whole question. It was unfortunate that some did not read the whole question before beginning to answer it, as part (a) asking about homeostasis was followed by part (b) how body temperature is maintained. Candidates who answered (a) very thoroughly wasted time repeating themselves in (b). They may have been unconsciously drawn to the body temperature example of (b) when answering (a).

Most candidates could give an example of homeostasis, even though many of their definitions for homeostasis were incomplete. Errors included forgetting to mention “internal” and “within limits.” The best answers included the concept of negative feedback and control through nerves and hormones

The majority of candidates had good knowledge of how sweating helps to control body temperature. They knew that sweat is released by the skin to cool an overheated body. In addition, some mentioned that heat removal occurs through evaporation of sweat. Since shivering, increased metabolism, and hair erection were all parts of one marking point, candidates were awarded a mark regardless of how many of these ideas were given. A common major misunderstanding involved the role of blood vessels. Too many suggested that blood vessels either moved closer or away from the skin surface for cooling or heating.  Many candidates did not understand vasodilation and vasoconstriction of arterioles. Furthermore, terminology was restricted to blood vessels, veins or capillaries. Only the rare candidate used the term arteriole. Other pertinent ideas often missed included normal body in degrees °C or °F, distribution of heat by the blood, and the importance of the hypothalamus with its thermoreceptors in monitoring body temperature and effecting needed responses.

Many candidates showed surprising command of the details in explaining the mechanism of ventilation. That understanding coupled with knowing the need for O₂ absorption and CO₂ removal was enough to gain most of the available marks. However, there were flaws. For example, the diaphragm was referred to as getting flattened or dome shaped with no reference to contraction or relaxation. The idea of the thoracic cavity increasing or decreasing was replaced with lungs increasing or decreasing with no reference to pressure. A number of candidates traced the respiratory system from mouth to alveoli. Some even included diagrams. All this was irrelevant since the mechanism of ventilation was not being addressed. The high surface area of the alveolicapillary interface was not often mentioned nor was the high concentration gradient of O₂ in the alveoli and the importance of blood to deliver O₂ to respiring cells.