Biology 2.5 -> the eye

Basic terms and the structure of the eye

Examples of Sense Organs

• Eyes

• Ears

• Nose

• Tongue

• Skin

Characteristics of living things

MRS GREN

• Movement

• Respiration

• Sensitivity

• Growth

• Reproduction

• Excretion

• Nutrition

What is a Stimulus

• A stimulus (plural stimuli) is a change in the surroundings

• A rabbit needs to know when it is in danger from a fox. The scent or sight of the fox is a stimulus.

How do eyes work as sense organs? (2)

• Contain light receptors

• Impulses from these receptors pass along nerve cells/neurons to your brain

Sclera

Protective, tough white outer coat

Cornea (3)

Clear part of sclera, allows light to enter and refracts light entering

Pupil

Hole in the centre of the Iris which allows light to enter

Iris

Muscle that alter the size of pupil to control the amount of light entering

Lens

Changed shape to focus light on the retina

Choroid (2)

• A pigmented layer which absorbs light to prevent reflection

• Contains blood vessels

Retina (2)

• Lighht-senstive layer; an image is formed here

• Impulses sent to optic nerve

Blind spot (2)

• Where the optic nerve connects to the retina

• No light sensitive cells here

Optic Nerve

Carries impulses from retina to brain