Sensitivity

Sensitivity is the ability to detect and respond to changes in the internal or external environment ¹. The stimulus may come from outside the body — light, sound, touch, temperature, chemicals — or from inside it, such as a fall in blood glucose concentration.

From Stimulus to Response

stimulus → receptor → coordinator (neurones / hormones) → effector → response

Sense organs are groups of receptor cells responding to specific stimuli: light, sound, touch, temperature and chemicals ¹. Electrical impulses travel along neurones, giving the nervous system a fast, short-lived response. Hormones are chemical substances produced by a gland, carried in the blood, which alter the activity of specific target organs — slower but longer-lasting.

Internal Environment: Homeostasis

Detection and response also happen inside the body. Homeostasis is the maintenance of a constant internal environment, controlled by negative feedback around a set point. Insulin from the pancreas decreases blood glucose by making the liver store glucose as glycogen; receptors and sweat glands in the skin control temperature.

Sensitivity in Plants

Plants respond to light and gravity by growth, not by nerves: auxin diffusing from the shoot tip stimulates uneven cell elongation, bending the shoot towards light.

Related

• Living Thing - Entity carrying out all seven life processes.
• Organism - Individual living thing.
• Movement - Effector response, often a change of place.
• Growth - Plant responses to stimuli are growth movements.
• Biology - Cambridge IGCSE life-science area.