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Having 2 eyes rather than 1 allows us to judge distance more accurately.

Each eye forms a slightly different image due to the eyes being several centimetres apart. The area of overlap is where we can judge distances accurately.

Internal structures of the eye showing the lens at the front of the eye covered by the cornea. The iris encircles the lens, with the pupil at the centre. The back of the eye is called the retina (

Cornea = tough, transparent layer at the front of the eye, allows light to enter and begins to bring it into focus.

Iris = coloured part containing muscles, which alter the diameter(size) of the pupil.

Lens = flexible, transparent, biconvex structure which focuses light on the retina.

Retina = light sensitive layer containing rods (sensitive to dim light) and cones (sensitive to bright light and colour). Light is converted to nerve impulses in the rod and cone cells - photoreceptors.

Optic Nerve = carries electrical nerve impulses from the retina to the brain.

Our judgement of direction of sound is more accurate using two ears rather than one.


Auditory canal = air-filled tube, which directs sound waves onto the eardrum.

Ear drum = thin membrane that vibrates and passes sound onto middle ear bones.

Middle ear bones = amplify and transmit sound vibrations from


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