b1.2.2

a) The nervous system enables humans to react to their surroundings and coordinate their behaviour.

b) Cells called receptors detect stimuli (changes in the environment).

Receptors and the stimuli they detect include:

• receptors in the eyes that are sensitive to light
• receptors in the ears that are sensitive to sound
• receptors in the ears that are sensitive to changes in position and enable us to keep our balance
• receptors on the tongue and in the nose that are sensitive to chemicals and enable us to taste and to smell
• receptors in the skin that are sensitive to touch, pressure, pain and to temperature changes

c) Light receptor cells, like most animal cells, have a…