Quick questions on Homeostasis and negative feedback control (QCE Biology Unit 2)

Internal conditions are not held perfectly constant. Each regulated variable (body temperature, blood pH, blood glucose, blood osmotic pressure, blood oxygen) oscillates within a narrow range around a set point. Homeostasis is a dynamic steady state, not a fixed value.

Every homeostatic control loop contains the same five components in the same order.

In a negative feedback loop, the response opposes the change that triggered it.

In positive feedback, the response amplifies the change. The variable accelerates away from the starting value until an external event terminates the loop. It is rare in physiology because it is unstable, and is reserved for processes that need to go to completion.

When core temperature climbs above the set point, the heat-loss centre activates the opposite effectors (sweat glands, vasodilation), restoring the set point.

Homeostatic mechanisms are sometimes split into: - Behavioural. Voluntary actions like seeking shade or putting on a coat. - Physiological. Involuntary internal adjustments (sweating, hormone release).

The variable oscillates around the set point, not at it.

QCAA mark schemes require all five components named in sequence.

It is unstable in general, but the body uses it deliberately for processes that need to amplify and terminate, like clotting and childbirth.

Homeostasis is a dynamic steady state. Levels change constantly; they are corrected toward the set point.