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  1. 1. How do we see?
  2. 2. - About 80% of the information that we receive from the environment is obtained through it. => The eye is the most important sense organ in our body. The eye
  3. 3. - We have a pair of eyes. - Each eye is held and protected in the orbit of the skull. orbit skull
  4. 4. - Each eye is held by eye muscles. - Eye muscle allows the eyeball to move up and down, left and right and in a circular way. eye muscle
  5. 5. The eyes of owls cannot move but their heads can nearly rotate 360 o . Do you know ?
  6. 6. The part of eye we can see is about 1/5 of total surface area of eyeball. Looking at the human eye 1 Label the drawing below. I Front part of the eye eyebrow eyelid protective coat eyelash pupil iris Activity Corner A
  7. 7. eyelid eyelash protective coat pupil iris Avoid sweat flowing into eyes Protect eyes Avoid foreign objects ( insects ) from entering eyes The eye is protected by the ______ , _______ and _______________. They prevent foreign objects from entering the eye. Light enters the eye through the _______ that is a hole at the centre of the ______ . eyebrow eyelid eyelash
  8. 8. In bright light pupil becomes smaller side view => Avoid strong light to damage eyes In dim light pupil becomes larger side view front view iris pupil front view
  9. 9. Hole allows light to pass through III Internal structures of the eye 3 Label the drawing below. Thick in middle , transparent and elastic ( thickness can be changed) A layer of white and elastic coat with the front part, cornea lens pupil protective coat Iris retina Have light-sensitive cells Connect with the brain optic nerve cornea jelly-like fluid
  10. 10. - Ox eyes and human eyes are similar in structure . - Dissecting an ox eye is a good way of studying the structures of our eyes.
  11. 11. - Provides attachment for eye muscles - Maintains the shape of eyeball - Protects internal structure of eyeball Functions of main parts of the eye Protective coat
  12. 12. Functions of main parts of the eye -acts as a protective layer -outermost part of the eye -allows light to enter in the eye cornea
  13. 13. - Focuses light on the retina Functions of main parts of the eye lens
  14. 14. - Focuses light on the retina - Maintains the shape of eyeball Functions of main parts of the eye jelly-like fluid
  15. 15. Functions of main parts of the eye iris under dim light under bright light
  16. 16. - Changes light into messages Functions of main parts of the eye retina
  17. 17. - Send messages to the brain Functions of main parts of the eye optic nerve
  18. 18. In dim light, pupils of cats and owls become very large. For cats and owls, larger pupils allow more light to enter the eyes, so they can move freely in dim light. Do you know ?
  19. 19. How is an image formed in the eye? - When we look at an object, => light ray is reflected from objects into our eyes. => The light passes through the cornea and lens and focuses on the retina to form an inverted image . inverted image
  20. 20. - When light reaches light-sensitive cells on the retina , => messages are sent to the brain by optic nerve => The brain interprets these messages as an upright image. How is vision produced ? => send messages
  21. 21. Showing the image formed in an ox eye : - Cut open the ox eye and stick a piece of semi-transparent paper on the back of retina. inverted image of candle
  22. 22. Our eyes can see the distant object (flying bird up in the sky) and the near object (a flower) clearly . How can the eyes focus on objects at different distances ?
  23. 23. - Focusing images on the retina is done by lens. How do we see things at different distances? By contraction or relaxation of the focusing muscles - thickness of lens can be changed. Focusing muscle
  24. 24. - Lens becomes thinner - Focusing muscles relax Near object - Focusing muscles contract - Lens becomes thicker Distant object
  25. 25. Why can we see colours ?
  26. 26. There are two types of light-sensitive cells on the retina: rods cones
  27. 27. - Differences between cones and rods : Cones Rods Number Condition Function Types Give colour images Give black and white images Work in bright light Work in dim light About 6 million About 1 . 2 billion One type (sensitive to red light, green light and blue light ) Three types
  28. 28. - The brain interprets messages from cones and forms coloured images.
  29. 29. A bull has no cones on its retina, therefore it cannot see any colour at all. Will the bull still run towards the cloth if the bullfighter uses a yellow one to replace the red one ? Do you know ?