The Senses How do we experience daily living through our senses?
Chapter 1_The World Through Our Senses
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Transcript of 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