chapter 1_the world through our senses

7/28/2019 Chapter 1_The World Through Our Senses

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CHAPTER 1CHAPTER 1THE WORLD THROUGH OUR SENSES

By: Ms Sumathi


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OUR SENSESOUR SENSES

Help us to be sensitive

to the changes

around us

These changes in the

surroundings are

known as stimuli LIGHT,SOUND and

SMELL are examplesof stimuli


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SENSORY ORGANS AND THEIRSENSORY ORGANS AND THEIR

STIMULISTIMULI


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SENSORY ORGANS, SENSES AND STIMULI


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PATHWAY FROM STIMULUS TOPATHWAY FROM STIMULUS TO

RESPONSERESPONSE

A stimulus will stimulate receptors to produce electricalmessages known as nerve impulses

These impulses are sent along the nerves to the brain. The brainthen sends out nerve impulses to the related effectors.

Effectors are parts of the body that carry out responses


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SENSE OF TOUCHSENSE OF TOUCH


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Sensory organ for touch Largest organ in the body Can detect changes in temperature(heat/cold),

pain, touch and pressureThe skin has special receptors to detect each of

these stimuli.The skin consists of two main layers, the outer

epidermis and the inner dermisThe epidermis is waterproof and tough, acting

as a protective layerThe dermis contains many blood vessels, sweat

glands and receptors.

THE SKINTHE SKIN


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Depends a lot on how close together thereceptors are and how deep they are.

For example, our fingertips are verysensitive to touch. They have many

receptors which lie very close to the skinsurface.

Our tongue,nose and lips are also verysensitive to touch.

The legs, elbows, the soles of the feet andthe back of our body are the least sensitiveto touch.

Sensitivity of the skinSensitivity of the skin


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Touch receptors are very sensitive toslight pressure. For example, they can tellyou whether an object is rough or smooth

Pain receptorsdetect pain. They lie veryclose to the skin surface so as to detectthe slightest pain.

Heat receptors are sensitive to heat Cold receptors are sensitive to cold Pressure receptorslie deep within the

skin and are sensitive only to heavy

pressure. For example, you feel theweight when you carry a heavy object.


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SENSE OF SMELLSENSE OF SMELL


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Our nose not only helps us with our breathing but it is alsothe sensory organ of smell

The two holes in our nose, called nostrils, open into a

hollow space called the nasal cavity. The mucous lining in the nasal cavity warms and moisten

the air before it enters the lung. The roof of the nasal cavity has many sensory cells or

receptors to detect smells.

Smells are actually chemicals present in the air. When sensory cells is stimulated by chemicals in air(from

food, perfume, flowers), sensory cells sends out nerveimpulses into the brain which interprets them as smell

We can get used to a smell when sensory cells stop

sending messages to brain and we no longer smell it The sensitivity of smell varies with individual.


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SENSE OF TASTESENSE OF TASTE


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Sensory organ for taste Can detect four basic tastes: salty, sweet,

sour and bitter

All other flavours are made up of thesebasic tastes Different areas of tongue are sensitive to

different tastes

Our tongue is lined with taste buds whichcontain many taste receptors

TongueTongue


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Our sense of smell improves our sense oftaste.

As we chew, some chemicals from the fooddissolve in our saliva and stimulate thetaste buds.

There are also some chemicals that moveinto our nasal passages which stimulates

the sensory cells in our nose.

Sense of taste and smellSense of taste and smell


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SENSE OF HEARINGSENSE OF HEARING

The ear is the sensory organ for hearing Has three main parts-the outer ear, the

middle ear and the inner ear


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Below are the path of the sound waves from the airto the brain:

The pinna collects sound waves and directs them

along the ear canal to the eardrum

When the sound waves hit the eardrum, it vibrates

The ossicles amplify the vibrations about 20 timesbefore transferring them to the oval window

How do we hear?How do we hear?


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Vibrations of the oval window set up waveswhich travel through the fluid in the cochlea

Receptors in the cochlea are stimulated to

produce nerve impulses.

1)

The auditory nerve carries the impulses to thebrain

The brain interprets the impulses assounds


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SENSE OF SIGHTSENSE OF SIGHT


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STRUCTURE OF EYESSTRUCTURE OF EYES


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Most people blink every 2-10 seconds. Each time you blink, you shut your eyes for 0.3 seconds,

which means your eyes are closed at least 30 minutes aday just from blinking.

If you only had one eye, everything would appear two-dimensional. (This does not work just by closing one eye.)

Owls can see a mouse moving over 150 feet away with lightno brighter than a candle.

The reason cat's and dog's eyes glow at night is because of

silver mirrors in the back of their eyes called the tapetum.This makes it easier for them to see at night.

Sense- Sational FactsSense- Sational Facts


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An ostrich has eyes that are two inchesacross. Each eye weighs more than thebrain.

A chameleon's eyes can look in oppositedirections at the same time.

A new born baby sees the world upsidedown because it takes some time for the

baby's brain to learn to turn the pictureright-side up. One in every twelve males is colour blind


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Our eyes are sensory organs of sight.The shape of each eye is a slightly

flattened ball.

The eyelid protects the front of the eye.The eyeball is held by muscles in the eye

sockets .Three layers make up the wall of the

eyeball : the sclera , the choroid and theretina .

THE EYES


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Functions of the Parts of theFunctions of the Parts of the

EyesEyes


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Let us see how our eyes work to give us thesense of sight:

Light rays travel from the object to the eye

As the light rays pass through the eye, they arerefracted (bent) by the cornea, aqueoushumour, lens and the vitreous humour

An upside down image(picture) is formed onthe retina

How do we see?How do we see?


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The photoreceptors on the retina send nerveimpulses along the optic nerve to the brain

The brain interprets the impulses and allows

us to see the object the right way up1)


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REFLECTION OF LIGHTTakes place when light rays fall on the surface of an opaque

object and bounce off it Example of reflection of light:

a) A student looking at his image on the surface of a lake

b) The formation of an image in a mirrorThe amount and direction of the reflected light depend on the

type of the surface the light falls on Plane mirrors and shiny metals are good light reflectors

because they have smooth and flat surfaces

OPAQUE-not able to be seen through/not transparent

LIGHT AND SIGHTLIGHT AND SIGHT


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A flat and smooth surface like a mirror reflectslight in a regular pattern. This is referred to asregular reflection(Figure 1)

Figure 1

When light falls on irregular surfaces like paperand cloth, the reflected light rays are scatteredin different directions and is referred to as adiffused reflection (Figure 2)


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When light strikes a smooth reflecting surface( for example, a mirror) at an angle to thenormal, it is reflected at the same angle on theopposite side of the normal


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Periscope Used in submarines to observe objects

outside the submarine

Kaleidoscope

Forms beautiful images when pieces ofpaper of various colours are put inside it

Mirror Dentist uses a mirror when examining a

patients teeth A convex mirror is placed at a bend on the

road so that drivers can see around thebend

Applications of theApplications of the

reflection of lightreflection of light


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Refraction of light

The refraction of light is the bending of light as itpasses from one transparent medium toanother. This happens when light travelsthrough different media such as air, water andglass

Occurs when speed of light changes. Happenswhen light travels 2 types of media that havedifferent densities

a) The speed of light decreases when light enters

a denser medium. Eg: from air to glassb) It increases when light enters a less dense

medium. Eg: from glass to air


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When light travels at an angle from a lessdense medium to a denser medium, it is

refracted towards the normal (Figure 3-airto glass block) When light travels from a dense medium to

a less dense medium, it is refracted away

from the normal. (Figure 3-glass block toair)


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1. The pond appears shallower than it reallyis

2.

3.

4.

5.

6. The drinking straw in the glass of water

appears to be bent

Phenomena of refractionPhenomena of refraction

of lightof light


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The dispersion of white light into its sevencomponent colours of the rainbow is aphenomenon of light refraction

Light refraction allows images to be formedon the retina of the eye

Lenses that refract light are used asmagnifying glasses in telescopes,microscopes and spectacles


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A person with normal vision sees distantand close objects clearly

The thickness of eye lens changes whennear or distant objects are focused

This process is known as accommodationThe common defects of vision are:

Vision defects and ways toVision defects and ways to

correct themcorrect them

Short-sightedness Long-sightedness Astigmatism

Colour blindness Presbyopia


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AccommodationAccommodation

CILIARY

BODY

SUSPENSORY

LIGAMENTS

EYE LENS

DISTANT OBJECT

RELAXES

CONTRACT

BECOMESTHINNER

COMPARISONCOMPARISON BETWEENBETWEEN LONGLONG


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COMPARISONCOMPARISON BETWEENBETWEEN LONG-LONG-

SIGHTEDNESS AND SHORTSIGHTEDNESS AND SHORT

SIGHTNESSSIGHTNESSConditio

n

Causes

FOCUS

CORRECTION


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Caused by an irregular surface of the cornea,or a lens that is not evenly curved

As a result, the vertical and horizontal rays fromthe image cannot be focused at the same time

Thus, the image formed on the retina is distortedand not very clear. A person suffering fromastigmatism sees some parts of an object moreclearly than others

Can be corrected by either wearing glasses withcylindrical lenses, wearing special contactlenses or surgery

ASTIGMATISMASTIGMATISM


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Due to a shortage of cone cells(colourreceptor cells) on the retina

Colour-blind people cannot see some or allcolours. Most of them cannot differentiatebetween red and green

This defect cannot be corrected becauseit is hereditary

COLOUR BLINDNESSCOLOUR BLINDNESS


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Common in old people. As a person getsolder, the eye lens becomes harder andless elastic. The muscles in the ciliarybody also lose their ability to

contract and relax As a result, both near and far objects

cannot be focused on retina

Corrected by wearing glasses with bifocallenses to see near and far objects clearly

PRESBYOPIAPRESBYOPIA


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Very tiny objects(bacteria, viruses, and atoms) cannot be

seen by the naked eye We also cannot see stars and planets that are very far

from Earth

THE BLIND SPOT When images fall on the blind spot, they cannot be seen.

This is because there are no photoreceptors on it

OPTICAL ILLUSIONS What we see depends not only on our eyes, but also on

our brain. Sometimes the brain distorts the images. This give rise to optical illusions. The image formed on the eye is accurate but the brain

plays a trick on us and makes the image misleading

LIMITATION OF SIGHTLIMITATION OF SIGHT


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Animal with stereoscopic vision have both eyes atthe front of the head

Animals with stereoscopic vision have visual fieldsthat overlap. Each eye sees a slightly different

image where the brain combines it so that theobject can be seen three dimensionally

This helps the animal to judge distancesaccurately

Predators such as tigers, owls and wolves havewell-developed stereoscopic vision

EREOSCOPIC VISIONEREOSCOPIC VISION


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MONOCULAR VISIONMONOCULAR VISION

Animals with monocular vision have eyesat the side of the head

The visual fields for animals with

monocular vision have little or nooverlapping

However, they have a wide field of vision This helps them to detect their enemies

from a wide range of directions. Prey such as rabbits, chickens and deer

have this type of vision


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DEVICES USED TO OVERCOME THE


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OPTICALINSTRUMENTS

DEVICES USED TO OVERCOME THELIMITATIONS OF SIGHT

An astronomer uses atelescope to studystars in the sky

The captain of a ship usesbinoculars to observe distantobjects

A microscope is

used to studysmall objects andspecimensmounted onslides

The crew of a submarine

uses a periscope to lookout for dangers above the

An ultrasound scanning device is usedto scan and see the fetus of apregnant mother


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Sound is a form of energy

Sounds are produced by vibrations When an object vibrates, kinetic energy is changed to

sound energy

The need for a medium for sound to travel Sound requires a medium to travel Most of the sounds that reach our ears are transferred

from a source either through air, liquids or solids. Sound travels faster through solids than liquids. This

is because particles are arranged closely in solids.They can pass on vibrations quickly

Sound travels the slowest through gases because theparticles are arranged loosely

Sound cannot travel through a vacuum

SOUND AND HEARINGSOUND AND HEARING


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When sound hits an obstacle, the sound wavewill either be absorbed or reflected by theobstacle depending on the type of the surfaceof the obstacle

Surfaces that are hard and smoothreflectsound. Walls of buildings, tunnels, mountainslopes, glass and metal are good soundreflectors but poor sound absorbers.

Surfaces that are soft and rough absorbsound. Carpets, curtains, cotton, sponge,rubber and soft boards are good soundabsorbers but poor sound reflectors

Reflection and absorptionReflection and absorption

of soundsof sounds


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HEARING DEFECTSHEARING DEFECTS


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May occur in one or all three parts of the ear

The main hearing defect is deafness. This refers to partial or total

hearing loss. Deafness can be caused by blockages of the auditory canal,

infections, accidents, the aging process or continuous exposure toloud noises

The build-up of earwax in the auditory canal can block sound waves

and cause temporary hearing loss Deafness can also result from a punctured eardrum

The ossicles in the middle ear may be fused together as a resultof an infection. This prevents the ossicles from moving freely. Ifthis condition is not treated immediately, it will result in total

hearing loss The inner ear may be damaged by local infections. Toxins are

produced as a result of diphtheria or scarlet fever. These toxinsdamage the cochlea and cause hearing loss

The sensory cells in the cochlea may be damaged by the exposureto loud sounds. This can eventually lead to hearing loss.

HEARING DEFECTSHEARING DEFECTS

STEREOPHONIC HEARINGSTEREOPHONIC HEARING


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Stereophonic hearing is the ability to hear using both ears

a) It enables us to determine the direction of the sound

accuratelyb) The ear nearer to the source of the sound receives a stronger

stimulus. It also receives the sound earlier than the otherear

c) Therefore, the impulse from this ear reaches the brain earlier

than the impulses from the other eard) The brain interprets these two different impulses. It also

determine the direction of the sound This hearing helps us determine accurately the location of the

source of a sound that warns of danger such as landslides. This

helps us avoid danger Prey that can accurately detect the direction of the sounds made

by their predators are able to make a quick escape. As such,stereophonic hearing is important for the survival of animals

STEREOPHONIC HEARINGSTEREOPHONIC HEARING


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Ear, nose and throat specialists use syringes andwarm water to remove the wax blocking theauditory canal

Fused or damaged ossicles can be replaced in a

surgery Punctured eardrums can also be repaired by

surgery. Damaged eardrums can be repairedor replaced by using membranes from otherparts of the body

Electronic gadgets can be implanted into theears to help some deaf people hear better

Correcting hearing defectsCorrecting hearing defects

Limitations of hearingLimitations of hearing


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The human ear has the ability to detect sounds in thefrequency range of20 Hz(hertz) to 20 000 Hz. Humans

cannot hear very low frequency or very high frequencysounds

The range of hearing varies from one individual to another

a) Children have eardrums that are more elastic. As a result,

they can hear betterb) As people age, their hearing deteriorates. Their eardrums

become less elastic . The range of sound frequenciesthat they can detect decreases. Their ability to hearhigh pitched sounds decreases.

c) A person exposed to constant loud noises experiences aloss of hearing. His range of hearing is smaller thanthat of a normal person

Frequencies exceeding 20 000Hz are called ultrasonicfrequencies. Humans cannot hear sound at thesefrequencies but some animals can.

Limitations of hearingLimitations of hearing

Ways to overcome ourWays to overcome our


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A doctor uses a stethoscope tolisten to the heartbeats of hispatients. The stethoscope makesthe soft heartbeats louder so thatthey can be heard

A teacher uses a loudspeaker tomake announcements duringschool assemblies in the school

field or the school hall Earphones are used to connect

sound gadgets such as the MP3player to our ears so that we can

listen to the music

Ways to overcome ourWays to overcome our

hearing limitationshearing limitations

S i li d iSti li d R i


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Plant respond to light, gravity and water. Some plants also

show responses to chemical substances and changes intemperature

The response of plants to a stimulus is called tropismTropism is a growth response in a particular direction. It

occurs slowly. It is not noticeable.

a) When a part of the plant grows towards the stimulus, theresponse is known as positive tropism

b) When a part of the plant grows away from the stimulus, theresponse is known as negative tropism

Tropic responses in plants include phototropism,

geotropism and hydrotropism Nastic movement and thigmotropism are responses of

plants to touch

Stimuli and Responses inStimuli and Responses in

PlantsPlants

11 Phototropism(plantPhototropism(plant


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Movement/growth of plants inresponse to light

a) Shoots grow towards light.(positively phototropic)

b) Roots grow away from light.(negatively phototropic)

1.1. Phototropism(plantPhototropism(plant

response to light)response to light)

2 Geotropism(plant2. Geotropism(plant


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Growth/movement of the tips of the shoots and

roots of plants in response to gravitya) Roots always grow downwards in the direction of

gravity(positively geotropism)

b) Shoots grow in the opposite direction togravity(negatively geotropism)

2. Geotropism(plant2. Geotropism(plant

response to gravity)response to gravity)

3 H d t i ( l t3 H d t i ( l t


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Plants growth/response to water is knownas hydrotropism

Roots tend to grow towards water.(positively hydrotropism)

The response of roots to water is strongerthan their response to gravity. They cangrow upwards or sideways, ignoring thepull of gravity

3. Hydrotropism(plant3. Hydrotropism(plant

response to water)response to water)

Nastic movementNastic movement


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Responses of a plant towards touch, light andheat

The opening and closing movement ofMimosapudica leaflets are examples ofnasticmovements

The direction of the response of the plant does

not depend on the direction of the stimulus. Themovement is reversible

Plants that trap insects have leaves which aresensitive to touch. The leaves of the Venus

flytrap and the pitcher plant will close whentouched especially by insects.

Nastic movementNastic movement


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Venus

flytap

Pitcher plant


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Tropic response in which the stimulus is touch orcontact

Roots grow away from solid objects such as stonesbut stems tend to grow towards the objects that

they come into contact witha) The passion flower, cucumber, long bean and

bitter gourd are plants with soft stems

b) These plants have tendrils which respond to thetouch stimulus

c) The tendrils curl around an object that touchesthem

ThigmotropismThigmotropism


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Passion flower CucumberLong beans

Bittergourd

Th i t f l tTh i t f l t


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Ensure that plants always obtain their basicneeds. Plants need sufficient water andlight for their survival

Forest plants depend on phototropism for

photosynthesis Plants roots grow downwards towards

gravity and into the soil which enablesthem to absorb water and mineral salts.Positive geotropism also help support theplants firmly in the soil

Positive hydrotropism enables plants to

The importance of plantThe importance of plant

responsesresponses

chapter 1_the world through our senses

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