- 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.

=>=> The eye is the most importantmost important sense organ in our body.

p.68Qp.68QThe Eye The Eye

- We have a pair of eyes.

- Each eye is held and protected in the orbit of the skull.

orbitorbitorbitorbit

skullskullskullskull

- 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 eye musclemuscle

eye eye musclemuscle

The eyes of owls cannot move buttheir heads can nearly rotate 360o .

The part of eye we can see is about 1/5 of total surface area of eyeball.

p.68p.68

Looking at the human eye

11 Label the drawing below.

I Front part of the eye I Front part of the eye

eyebrow

eyelid

protective coat

Eyelash

pupil

iris

Activity Corner Activity Corner AA

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 ____________.

eyelideyelid eyelasheyelash

protective coatprotective coat

pupilpupil

irisiris

eyebroweyebroweyebroweyebrow

eyelideyelideyelideyelid

eyelasheyelasheyelasheyelash

Avoid sweat flowing into eyes

Protect eyes

Avoid foreign objects (insects) from entering eyes

II How does the eye work in dim light and bright light?

II How does the eye work in dim light and bright light?

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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).

smallersmaller

Do not examine the eye with the torch for Do not examine the eye with the torch for too long.too long.

Watch out ! Watch out !

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.

irisiris

smallersmaller

lessless

largerlarger moremore

In bright lightIn bright lightIn bright lightIn bright light

pupil becomes smallerpupil becomes smaller

side viewside view front viewfront view

irisirisirisiris

pupilpupilpupilpupil

=>=> AvoidAvoid strong light strong light to to damage eyesdamage eyes

=>=> AvoidAvoid strong light strong light to to damage eyesdamage eyes

In dim lightIn dim lightIn dim lightIn dim light

pupil becomes largerpupil becomes larger

side viewside view front viewfront view

HoleHole allows allows light to pass light to pass

throughthrough

HoleHole allows allows light to pass light to pass

throughthrough

III Internal structures of the eyeIII Internal structures of the eye

33 Label the drawing below.Thick Thick in middlein middle, transparent , transparent and and elastic elastic ((thickness thickness can be changed)can be changed)Thick Thick in middlein middle, transparent , transparent and and elastic elastic ((thickness thickness can be changed)can be changed)

A layer of A layer of white and elastic white and elastic coat coat with the front part,with the front part, cornea cornea

A layer of A layer of white and elastic white and elastic coat coat with the front part,with the front part, cornea cornea

lens

pupil

protective coat

Iris

retina

Have Have light-light-sensitive cellssensitive cellsHave Have light-light-sensitive cellssensitive cells

Connect with Connect with the the brainbrainConnect with Connect with the the brainbrain

optic nerve

jelly-like fluidjelly-like fluid

cornea

What is the What is the colour colour of of pupilpupil??

- Ox eyes and human eyes are similar in structure.

- Dissecting an ox eye is a good way of studying the structures of our eyes.

Protective Protective coatcoatProtective Protective coatcoat

- Provides attachment for eye muscles

- Maintains the shape of eyeball

- Protects internal structure of eyeball

Functions of main parts of the eyeFunctions of main parts of the eye

- Focuses light on the retina

Functions of main parts of the eyeFunctions of main parts of the eye

corneacorneacorneacornea

- Focuses light on the retina

lenslens lenslens

Functions of main parts of the eyeFunctions of main parts of the eye

- Focuses light on the retina

- Maintains the shape of eyeball

jelly-like jelly-like fluidfluid

jelly-like jelly-like fluidfluid

Functions of main parts of the eyeFunctions of main parts of the eye

What is the function of iris?

irisirisirisiris

under

dim light

underunder

bright bright lightlight

Functions of main parts of the eyeFunctions of main parts of the eye

- Changes light light into messages

retinaretinaretinaretina

Functions of main parts of the eyeFunctions of main parts of the eye

- Send messages to the brain

optic optic nervenerveoptic optic nervenerve

Functions of main parts of the eyeFunctions of main parts of the eye

In dim light, In dim light, pupils ofpupils of cats cats and and owls owls becomebecome

very large.very large.

For cats and owls, For cats and owls, larger pupils larger pupils allow allow

more light more light to enter the to enter the eyes, eyes, so they canso they can move move

freely freely in dim light. in dim light.

p.72p.72How is an image formed in the eye? How is an image formed in the eye?

- When we look at an object,

=> => lightlight ray ray is reflected from objects 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 imageinverted image

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

- When light light reachesreaches 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?How is vision produced?

=> => send messages

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Showing the image formed in an ox eye: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.72p.72

Making of a pinhole cameraMaking of a pinhole cameraMaking of a pinhole cameraMaking of a pinhole camera

Our eyes work in a similar way to cameras.

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Follow Follow the stepsthe steps below to make a below to make a pinhole pinhole cameracamera and see what and see what happens happens on the on the screen.screen.

1 1 PaintPaint the inside of a paper cup the inside of a paper cup dark. dark.

22 MakeMake a a small holesmall hole on the on the basebase with a pin.with a pin.

33 StretchStretch a piece of tracing a piece of tracing paper paper over the over the top of the top of the cup.cup.

Little Scientist

44 Switch off Switch off the light of a room. the light of a room. LightLight a small candle. a small candle.

View the candle flame through the through the pinhole camera about pinhole camera about 50 cm50 cm away. away.

Principle of forming image in pinhole Principle of forming image in pinhole cameracameraPrinciple of forming image in pinhole Principle of forming image in pinhole cameracamera

- Candle flame emits rays of lights.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

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

=> Overlap => Overlap withwith 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

- Convex lens can converge lights.

If we put a convex lens in front of the hole, the image will be brighter and clearer.

p.73p.73Our eyes can see the distant object (flying bird up in the sky) and the near object (a flower) clearly.

How can the eyesHow can the eyes focus on objects focus on objects at at different distancesdifferent distances??

- Focusing images on the retina is done by lens.

How do we see things at different distances? How do we see things at different distances?

ByBy contraction contraction or or relaxation relaxation of the of the focusing musclesfocusing muscles

ByBy contraction contraction or or relaxation relaxation of the of the focusing musclesfocusing muscles

- From Experiment Centre 11.1 Experiment Centre 11.1, we know that thickness of lens can be changed.

Focusing Focusing musclemuscleFocusing Focusing musclemuscle

Distant Distant objectobjectDistant Distant objectobject

- Lens becomes thinnerthinner

- Focusing muscles relaxrelax

Near Near objectobjectNear Near objectobject

- Focusing muscles contractcontract

- Lens becomes thickerthicker

p.73p.73

You’ve wornworn two socks of different colors!

You’ve wornworn two socks of different colors!

Can you Can you explainexplain thisthis case? case?

Can you Can you explainexplain thisthis case? case?

p.74p.74Why can we see colours ? Why can we see colours ?

There are two types of light-sensitive cellson the retina:

rodsrodsrodsrodsconesconesconescones

- Differences between cones and rods:

Cones Rods

NumberNumber

ConditionCondition

FunctionFunction

TypesTypes

Give colour images

Give black and white images

Work in bright light

Work in dim light

About 6 million6 million About 11..2 billion2 billion

One typeOne typeOne typeOne type(sensitive to red light, green light and blue light)

Three typesThree typesThree typesThree types

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

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

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

A bull has no cones on its retina, therefore it cannot see any colour at all.

WillWill the bull the bull still run towards the cloth if the still run towards the cloth if the bullfighter uses a bullfighter uses a yellow oneyellow one to replace the to replace the red onered one ??

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Don’t look at me…

Alamak.........