2. How do we see? 11.2 How do we see?

3. - In Check-point 1, you can see that we are able to distinguish between all the pairs of objects by our eyes. - About 80% of the information that we receive from the environment is obtained through it. =>most important => The eye is the most important sense organ in our body. p.68 The eye

4. - We have a pair of eyes. - Each eye is held and protected in the orbit of the skull. orbit ( 眼窩 ) skull ( 顱骨 )

5. - 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

6. The eyes of owls cannot move but their heads can nearly rotate 360 o.

7. The part of eye we can see is about 1/5 of total surface area of eyeball. p.68 Looking at the human eye 1 1 Label the drawing below. I Front part of the eye eyebrow ( 眼眉 ) eyelid ( 眼瞼 ) protective coat ( 鞏膜 ) eyelash ( 眼睫毛 ) pupil ( 瞳孔 ) iris ( 虹膜 ) Activity Corner A

8. _____________ _______________. _______ ______ 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 ______.eyelideyelash protective coat pupil iriseyebroweyebrow eyelideyelid eyelasheyelash Avoid sweat flowing into eyes Protect eyes Avoid foreign objects (insects) from entering eyes

9. II How does the eye work in dim light and bright light? p.69 2 2 Hold a torch about 10 cm from your classmate’s eye. What happens to the size of pupil? The pupil becomes ________ (smaller/larger). smaller Do not examine the eye with the torch for too long. Watch out !

10. The _______ controls the size of the pupil. In bright light, the pupil becomes _________ to allow _______ light to enter the eye. In dim light, the pupil becomes _______ to allow _______ light to enter the eye. iris smaller less largermore

11. In bright light pupil becomes smaller side view front view irisirispupilpupil =>Avoid strong light to damage eyes => Avoid strong light to damage eyes In dim light pupil becomes larger side view front view

12. Hole allows light to pass through III Internal structures of the eye 3 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 ( 晶狀體 ) pupil ( 瞳孔 ) protective coat ( 鞏膜 ) Iris ( 虹膜 ) retina ( 視網膜 ) Have light- sensitive cells Connect with the brain optic nerve ( 視神經 ) jelly-like fluid cornea ( 角膜 )

13. What is the colour of pupil?

14. - Ox eyes and human eyes are similar in structure. - Dissecting an ox eye is a good way of studying the structures of our eyes.

15. Protective coat - Provides attachment for eye muscles - Maintains the shape of eyeball - Protects internal structure of eyeball Functions of main parts of the eye

16. - Focuses light on the retina Functions of main parts of the eye corneacornea

17. - Focuses light on the retina lens lens Functions of main parts of the eye

18. - Focuses light on the retina - Maintains the shape of eyeball jelly-like fluid Functions of main parts of the eye

19. What is the function of iris? irisiris under dim light under bright light Functions of main parts of the eye

20. - Changes light into messages retinaretina

21. - Send messages to the brain optic nerve Functions of main parts of the eye

22. 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.

23. p.72 How is an image formed in the eye? - When we look at an object, => light ray is reflected from objects => 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

24. Look at the alphabet on the right: Which of the diagrams below shows the image of the alphabet on your retina? p p b b q q d d

25. light reaches - 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 p.72

26. 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 p.72

27. Making of a pinhole camera Our eyes work in a similar way to cameras. p.72 Follow the steps below to make a pinhole camera and see what happens on the screen. 1 Paint the inside of a paper cup dark. 2 Make a small hole on the base with a pin. with a pin. 3 Stretch a piece of tracing paper over the top of the cup. Little Scientist

28. 4 Switch off the light of a room. Light a small candle. Light a small candle. through the pinhole camera about 50 cm away. View the candle flame through the pinhole camera about 50 cm away.

29. Principle of forming image in pinhole camera rays of lights. - Candle flame emits rays of lights. => => Rays fall on the screen and form image => => Hole of pinhole camera can only allow part of the rays to pass through. inverted, smaller than the object

30. the hole of pinhole camera is If the hole of pinhole camera is too large, what happens to the image formed on the screen?

31. => Overlap with => Overlap with each other - If the hole is too large: => => Rays passing into the camera through the hole increase => => Form many images of candle on the screen => => Form brighter but more blurred images

32. - Convex lens can converge lights. If we put a convex lens in front of the hole, the image will be brighter and clearer.

33. p.73 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?

34. - 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 ( 睫狀肌 ) Experiment Centre 11.1 - From Experiment Centre 11.1, we know that thickness of lens can be changed. Focusing muscle

35. Distant object thinner - Lens becomes thinner relax - Focusing muscles relax Near object contract - Focusing muscles contract thicker - Lens becomes thicker p.73

36. worn You’ve worn two socks of different colours! Can you explain this case?

37. p.74 Why can we see colours ?

38. There are two types of light-sensitive cells on the retina: rodsrods conescones

39. - 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 6 million About 6 million 1.2 billion About 1.2 billion One type (sensitive to red light, green light and blue light) Three types

40. Colours are formed by mixing of three primary colours: red, green and blue in different proportions.

41. Screens TV can show various colours. Screens of TV can show various colours. This depends on mixing of three primary colours of light in different proportions.

42. - The brain interprets messages from cones and forms coloured images.

43. 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 ? p.74