They are more sensitive in dim light but can't sense colour
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Name two facts about cones?
They are sensitive to different colours but are not so good in dim light
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What is the information from light converted into?
Electrical impulses
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What carries these impulses?
The optic nerve
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Where from and to?
From the receptors to the brain
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What can the eye do because it's elastic?
It can focus light onto the retina
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How does it do that?
By changing the shape of the lens
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How does it look at distant objects?
The ciliary muscle relaxes, which allows the supersensory ligaments to pull tight.
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What does this do?
It pulls the lens into a less rounded shape so light is refracted less
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How does it look at close objects?
The ciliary muscle contracts , which slackens the supersensory ligaments
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What does this do?
The lens becomes a more rounded shape, so light is refracted more
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What are long- and short-sightedness caused by?
Structural abnormalities
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What are long-sighted people unable to do?
Focus on near objects
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When does this occur?
When the lens is the wrong shape and doesn't bend the light enough or the eyeball is too short
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In long-sightedness, where is the light from the close objects brought into focus?
Behind the retina
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What type of lens do you use to correct it?
A convex lens
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What are short-sighted people unable to do?
Focus on distant objects
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When does this occur?
When the lens is the wrong shape shape and bends the light too much or the eyeball is too long
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Where the light from distant objects brought into focus?
In front of the retina
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What type of lens do you use to correct it?
A concave lens
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What can't colour blind do?
They can't tell the difference between certain colours
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What is the most common form of the disorder?
Red-green colour blindness
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What is it caused by?
When red or green cones in the retina are not working properly
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Why is there no cure for colour blindness at the moment?
Because the cone cells can't be replaced
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What is a cataract?
A cloudy patch on the lens
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What does it do?
Stops light from being able to enter the eye normally.
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People with cataracts are likely to have what?
Blurred vision
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They may also experience what?
Colours looking less vivid and have difficulty seeing in bright light.
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How can a cataract be treated?
By replacing the faulty lens with an artificial one.
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Explain how a structural problem with the eye may cause a person to be long-sighted?
The lens may be the wrong shape/ the eyeball may be too short [1 mark], meaning that light from near objects is brought into focus behind the retina [1 mark].
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