Revise Biology Paper 2 Unit 5 Homeostasis & Response Key Concepts

Nervous system

Homeostasis and Response

Homeostasis is the regulation of a constant internal environment. The conditions are maintained to ensure optimum conditions for metabolism and changes in response to both internal and external fluctuations.

In humans, homeostasis regulates the blood glucose (sugar) levels, the body temperature, CO2 levels and water levels.

The levels are monitors and regulated by automatic control systems which can be either nervous responses (coordinated by the nervous system) or chemical responses (coordinated by the endocrine system). Information about the environment is called a stimulus and is detected by a receptor. The information is processed by a central coordination system and a response is initiated by an effector.

The Reflex Arc

A reflex arc begins with the stimulus e.g. a bee sting or a hot object on the skin. The stimulus is detected by the receptor cells and an electrical impulse is transmitted along the sensory neuron. The impulse is passed through relay neurons in the spinal cord or the unconscious areas of the brain. The response is coordinated automatically and sent along the motor neuron to the effector cells.


Hormones are chemical messengers transported in the bloodstream to an effector where they can activate a response. They are produced and released from glands around the body which all make up the endocrine system.

The pituitary gland produces a range of hormones including FSH and LH which help to regulate the menstrual cycle. The pituitary gland acts as a master gland because many of the hormones it releases control and coordinate the release of other hormones from other glands in the body.

Download our Homeostasis & Response Knowledge Organiser for a summary of everything you need to know for the exam.

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