A level Biology exam revision resources written by A level Examiners


Homeostasis is a control process that maintains conditions. So when a condition (e.g. temperature, or glucose concentration in blood) deviates from a set point, or norm a corrective mechanism is triggered by the very condition which is to be regulated. In the case of glucose an increase in the amount of glucose triggers a process to decrease it. Conversely, a decrease in the glucose level triggers a process to increase it. In both cases the result is a reasonably constant level of glucose. When a change in a condition brings about the opposite effect it is termed as a negative feedback.

Negative feedback can be defined as a homeostatic mechanism in which a change in certain condition triggers a response which reduces the effect of the change.

Negative feedback is the mechanism of homeostasis and it responds to change, which means that all the conditions controlled by homeostasis will fluctuate within limit. As they only trigger control by changing.

The negative feedback system for all the conditions controlled must have some common components. They all have:

  • receptors (or sensors) capable of detecting the change;
  • a control mechanism capable of initiating corrective measure;
  • effectors that can carry out the corrective measures.

The next sections will examine two specific examples of homeostasis in detail; temperature regulation and blood glucose regulation.

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