IGCSE · Practice questions · Homeostasis

Every change, reversed.

Six original Cambridge-style questions on homeostasis, blood glucose control, Type 1 diabetes, a glucose tolerance graph, the parts of the skin and the control of body temperature.

Original questions All questions on this page are original work, written in the Cambridge IGCSE style. They are not from past papers. They test the same concepts and skills the syllabus rewards.

Keep these straight

Detect, respond, reverse.

Homeostasis: maintenance of a constant internal environment. Insulin lowers blood glucose.
Negative feedback (Extended): a change from the set point triggers a response that reverses it.
Glucose (Extended): high: insulin, glucose to glycogen in the liver. Low: glucagon, glycogen to glucose.
Temperature (Extended): hot: vasodilation, sweating. Cold: vasoconstriction, shivering, hairs up, insulation.

Recall

[2 marks]

Define homeostasis and state the effect of insulin on blood glucose concentration.

Homeostasis is the maintenance of a constant internal environment. ✓
Insulin decreases (lowers) the blood glucose concentration. ✓

Explain

[5 marks]

Extended. Explain how blood glucose concentration is returned to normal after a meal rich in carbohydrate, using the idea of negative feedback.

Blood glucose rises above the set point after the meal. ✓
The pancreas detects the rise and secretes insulin into the blood. ✓
Insulin causes the liver to convert glucose into glycogen and store it (and other cells take up more glucose). ✓
Blood glucose falls back towards the set point. ✓
This is negative feedback: the change causes a response that reverses it; as glucose falls, less insulin is secreted. ✓

Data

[4 marks]

Extended. Two people each drank a glucose solution at time 0. Their blood glucose was measured.

Time / min	0	30	60	120
Person A / mmol dm⁻³	5.0	7.8	6.1	5.1
Person B / mmol dm⁻³	7.5	13.9	15.2	12.8

(a) Which person is likely to have Type 1 diabetes? Give two pieces of evidence. (b) Outline how this condition is treated.

(a) Person B. ✓
Their glucose is higher even before the drink (7.5 compared with 5.0), and it keeps rising to 60 min and is still high (12.8) at 120 min, while person A returns to about 5.0. ✓
(b) Insulin injections (or an insulin pump), with regular measurement of blood glucose. ✓
Control of diet, especially carbohydrate intake, and planning exercise to keep glucose within the normal range. ✓

Recall

[4 marks]

Extended. A diagram of a section through human skin is labelled A to G. State the function of: (a) sweat glands, (b) hair erector muscles, (c) fatty tissue, (d) receptors.

(a) Sweat glands secrete sweat on to the skin surface; its evaporation cools the body. ✓
(b) Hair erector muscles contract to raise the hairs, trapping a layer of insulating air. ✓
(c) Fatty tissue insulates the body, reducing heat loss. ✓
(d) Receptors detect changes in temperature and send impulses along sensory neurones. ✓

Explain

[5 marks]

Extended. A person sits outdoors on a cold winter day. Explain how their body keeps its core temperature close to 37 °C. Refer to vasoconstriction in your answer.

The brain detects the fall in blood temperature (and receives impulses from cold receptors in the skin). ✓
Vasoconstriction: arterioles supplying the skin surface capillaries narrow, so less blood flows near the surface and less heat is lost by radiation. ✓
Shivering: muscles contract rapidly, and the respiration releases heat. ✓
Sweating stops, so no heat is lost by evaporation of sweat; hairs are raised to trap air. ✓
The layer of fatty tissue insulates the body; together these return the temperature towards the set point (negative feedback). ✓

Analysis

[3 marks]

Extended. Explain why sweating cools the body less effectively in very humid air, and why the skin of a person looks red after exercise.

Sweat cools the body only when its water evaporates, transferring heat away from the skin. ✓
In humid air the air is already nearly saturated with water vapour, so less sweat evaporates and less heat is lost. ✓
After exercise vasodilation widens the arterioles to the skin capillaries, so more blood flows near the surface, making the skin look red and losing more heat. ✓

Mark this once you have attempted all six and checked your working. It records a Practiced badge on the topic and adds a one-time bonus. Revealing the solutions alone does not count.