2.91, 2.92 - The Eye

Edexcel IGCSE Biology

draw/describe the structure of the eye

what is the function of the cornea?

transparent lens that refracts light as it enters the eye

function of the iris?

controls how much light enters the pupil

what is the function of the lens?

transparent disc that can change shape to focus light onto the retina

what is the function of the retina?

contains light receptor cells

* rods detect light intensity
* cones detect colour

what is the fucntion of the optic nerve?

sensory neurone that carries impulses between the eye and brain

what is the function of the pupil?

hole that allows light to enter the eye

what is the ciliary muscle?

a ring of muscle that contracts and relaxes to change the shape of the lens

what are suspensory ligaments?

ligaments that connect the ciliary muscle to the lens

what is the sclera?

the strong outer wall of hte eyeball that helps to keep the eye in shape and provides a place of attachment for the muscles that move the eye

what is the fovea?

a region of the retina with the highest density of cones (where the eye sees in particularly good detail)

what is the blind spot?

the point at which the optic nerve leaves the eye, where there are no receptor cells

what happens when an object is far away?

* light is refracted less
* ciliary muscles relax
* suspensory ligaments tight
* lens thinner

what happens when an object is close?

* light is refracted more
* ciliary muscles contract
* suspensory ligaments slack
* lens fatter

what happens to the eye in dim light?

* photoreceptors detect change in environment
* radial muscles contract
* circular muscles relax
* pupil dilates
* more light enters the eye

what happens to the eye in bright light?

* photoreceptors detect change in environment
* radial muscles relax
* circular muscles contract
* pupil constricts
* less light enters the eye