▶️ Answer/Explanation
(a) homeostasis; negative feedback
Explanation: The human body maintains a constant internal temperature through homeostasis, which is the process of maintaining stable internal conditions despite changes in the external environment. When temperature deviates from the set point, negative feedback mechanisms work to return it to normal. For example, if body temperature rises, mechanisms like sweating are triggered to cool the body down, while if temperature drops, shivering generates heat to warm the body up.
(b)(i)
L – sweat gland
O – receptor(s)
J – (hair) erector muscle
Explanation: These structures are key components of the skin’s thermoregulatory system. Sweat glands produce sweat for cooling, receptors detect temperature changes, and hair erector muscles control hair position to trap insulating air when contracted.
(b)(ii)
When external temperature decreases:
- Temperature receptors in the skin detect the cold stimulus
- Nerve impulses are sent to the hypothalamus in the brain
- Hair erector muscles contract, making hairs stand up to trap insulating air
- Blood vessels near the skin surface constrict (vasoconstriction) to reduce heat loss
- Sweat glands reduce or stop sweat production to conserve heat
- Shivering may occur as muscles contract rapidly to generate heat
- Fatty tissue under the skin acts as insulation
Explanation: This coordinated response helps maintain core body temperature by reducing heat loss and increasing heat production when exposed to cold environments. The hypothalamus acts as the body’s thermostat, coordinating these responses through the nervous and endocrine systems.
(c)(i) pancreas
Explanation: Glucagon is secreted by the alpha cells in the islets of Langerhans within the pancreas, which is both an exocrine and endocrine gland located behind the stomach.
(c)(ii) Glucagon stimulates the breakdown of glycogen to glucose in the liver, increasing blood glucose concentration.
Explanation: When blood glucose levels drop too low, glucagon is released. It acts primarily on liver cells, triggering the conversion of stored glycogen into glucose through glycogenolysis. This glucose is then released into the bloodstream, raising blood sugar levels back to normal. Glucagon works in opposition to insulin to maintain glucose homeostasis.
