Question 1

What is the difference between negative and positive feedback?

Accepted Answer

Negative feedback reverses a change in a controlled condition, bringing it back towards the set point. For example, if body temperature rises, mechanisms like sweating cool the body down. Positive feedback amplifies a change, moving the system further away from the set point. This is seen in childbirth, where oxytocin release increases contractions, which in turn stimulate more oxytocin release until delivery. Negative feedback is common in homeostasis; positive feedback is rarer and usually part of a process that needs to be completed quickly.

Question 2

How does the body control blood glucose levels?

Accepted Answer

Blood glucose is controlled by the pancreas, which contains alpha and beta cells in the islets of Langerhans. When blood glucose rises (e.g., after a meal), beta cells release insulin, which causes liver and muscle cells to take up glucose and convert it to glycogen (glycogenesis). When blood glucose falls (e.g., during exercise), alpha cells release glucagon, which stimulates the liver to convert glycogen back to glucose (glycogenolysis) and also produce glucose from amino acids (gluconeogenesis). This is a classic negative feedback loop.

Question 3

What is the role of the hypothalamus in homeostasis?

Accepted Answer

The hypothalamus is a key coordination centre in the brain that maintains homeostasis by receiving information from receptors and initiating responses. It contains thermoreceptors that detect blood temperature and also receives input from peripheral thermoreceptors. In thermoregulation, the hypothalamus triggers mechanisms like vasodilation, sweating, shivering, and vasoconstriction. It also controls the pituitary gland, which releases hormones that regulate water balance (ADH), growth, and stress responses. The hypothalamus is essential for integrating nervous and endocrine signals.

Question 4

Why is homeostasis important for enzyme function?

Accepted Answer

Enzymes are proteins that catalyse metabolic reactions, and their activity is highly sensitive to temperature and pH. Each enzyme has an optimum temperature and pH at which it works best. If body temperature deviates too much from 37°C, enzymes can denature (lose their shape) and stop working, leading to metabolic failure. Similarly, blood pH must be maintained around 7.4 for enzymes like those in cellular respiration to function. Homeostasis ensures that these conditions remain within a narrow range, allowing enzymes to work efficiently.

Question 5

What is the difference between the nervous and endocrine systems?

Accepted Answer

The nervous system uses electrical impulses (action potentials) transmitted along neurones to deliver rapid, short-lived responses. It targets specific cells (e.g., muscles or glands) and communication is via neurotransmitters at synapses. The endocrine system uses hormones, which are chemical messengers released into the blood. Responses are slower but longer-lasting, and hormones can affect many target cells throughout the body that have specific receptors. Both systems work together to coordinate responses; for example, the hypothalamus links the two.

Question 6

How does the body maintain a constant temperature?

Accepted Answer

Body temperature is regulated by the hypothalamus, which acts as a thermostat. When temperature rises, the hypothalamus triggers vasodilation (widening of blood vessels in the skin) to increase heat loss, and sweating to cool the body via evaporation. When temperature falls, it causes vasoconstriction (narrowing of blood vessels) to reduce heat loss, shivering to generate heat, and piloerection (hair standing up) to trap a layer of air for insulation (though less effective in humans). These responses are coordinated by negative feedback.

Communication and homeostasis

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