Science // Biology // B1 // Eyes

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    • Some photoreceptors can detect several different stimuli but they are specialised to detect one type of stimulus;
      • Light
        • Photoreceptors in the eye
      • Sound
        • Vibration receptors in the ears
      • Touch, pain, pressure
        • Different receptors in the skin
      • Taste, smell
        • Chemical receptors in the tongue and nose
      • Position of the body
        • Receptors in the ears
    • A sense organ is a group of receptors gathered together with some other structures; the other structures help the receptors to work more efficiently.
      • Distant object and close object
      • Usually these effectors are muscles and they respond by contracting, they could be glands and they may respond by releasing an enzyme. Many responses are reflexes.
    • Many people have problems with their eyesight.
      • Long or short sight is caused by the eyeball or lens is the wrong shape, and the tretament to long sight and short sight is by wearing the right lenses, and also cornea surgery can be used.
      • Red-green colour blindness can be caused by the lack of certain cones in the retina but there is no treatment for this.
      • Poor accommodation can be caused by lens becoming less elastic in senior citizens. The treatment for this is to wear glasses with half convex and half concave lenses.
    • Eyes are also used to judge distances. Animals that hunt usually have eyes on the front of their head, same as human's. But each eye has a slightly different image of each object. This is called binocular vision and it can be used to judge distances.
      • Animals that are being hunted usually have eyes on the sides of their heads. This gives monocular vision and they cannot judge distances so well. But can see all around.
    • The structure of the eye


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