CHAPTER 1

THE WORLD THROUGH OUR SENSES

SENSORY ORGAN AND THEIR FUNCTION SENSORY ORGAN

Sensory organs are organs that detect stimuli.2. A stimulus is a change in the environment that produces a reaction in a living organism.3. Sense is the ability of the sensory organ to detect a stimulus.Each sensory organ is sensitive to only certain stimuli.

EYESense of :SIGHTStimulus : LIGHTFunction : to see objectNOSESense of : SMELLStimulus : CHEMICAL SUBSTANCES IN THE AIRFunction : to detect objectEARSense of : HEARINGStimulus : SOUNDFunction : to detect soundSKINSense of :TOUCHStimulus : COLD,HEAT PAIN, PRESSURE,TOUCHFunction : to detect heat, type of surfaceTONGUESense of :TASTEStimulus : CHEMICAL SUBSTANCESFunction : to taste flavour

SENSORY ORGANSEYEEARTONGUESKINNOSELIGHTSIGHTSTIMULIis detected by the sense ofTASTECHEMICALSUBSTANCESHEARINGSOUNDSMELLTOUCHPRESSUREHEATCOLDPAINTOUCH

7. The pathway from stimulus to response is : Stimulus Sensory organsNerves Brain Nerves Response 8. Nerves connect the brain to all parts of the body and send signals from the sensory organs to the brain.9. The brain interpret the signal and send back to the muscle or organs by nerve to respond. 10. A response is a reaction produced in answer to a stimulus.11. The brain controls all the actions and response of the body.

When a girl touches a cat, the receptors in the palm of her hand receives the stimulus (touch). The receptors produce nerve impulses which are sent along nerves to the brain to be interpreted. The touch is felt as soft and warm. The brain then produces new impulses. These are sent along the nerves to the effectors (muscles in the hand). This causes the hand to cares the cat as a response.

SENSE OF TOUCH

Receptors are special structures in our sensory organ that detect stimuli.There are many types of receptors in our body.Each type of receptor can detect only one stimulus.The parts of our body that contain receptors are called sensory organs and these receptors have nerves.Skin is the sensory organ that gives us the sense of touch.The receptors in skin are able to detect TOUCH,PRESSURE, HEAT , PAIN and COLD.

EpidermisDermisFat layerSENSE OF TOUCHMade up of dead cells,act as protective layerInner layer of skin,consist of living cells, Blood vessels and sweat gland.Act as insulator

Pain receptor-detect paintouch receptor-detect slight pressure on skinHeatReceptor-detect hotColdReceptor-detect coldPressurereceptor-detect pressureSweat glandErectormuscle

The skinSensoryorganHas five types ofreceptorsSensitivityResponds to pain, touch,Pressure , heat, cold pain receptors touch receptors heat receptors cold receptors pressure receptors thickness of skin number of sensory nerves depends on

When a receptor is stimulated , the information ( impulse ) is sent through the nerves to the brain for interpretation.8. The sensitivity of the skin depends on the : a. Thickness of the epidermis the thinner the epidermis, the more sensitive the skin to the stimulusNumber of the receptors the more receptors found on the skin, the more sensitive is that part of the skin.

The parts of the body that have thin epidermis and many receptors sensitive to touch are : a. lips b. fingertips c. armpit d. the back of the neck e. behind the ears

The parts of the body that are not so sensitive to touch are the : a. elbow b. knee c. palm of the hand d. sole of the foot e. buttocks

11.Braille is a code made up of small raised dot on paper. Blind people use their sense of touch to read Braille.

12.Injections are usually given at the upper arm and buttocks.

12.Types of receptors and their functions :

Type of receptorsFunctionsTouch and pressure To feel touchTo identify the texture, size and shape of an object.Pain Sensitive to painHeat and cold To detect temperature To know how hot or cold an object is.

SENSE OF SMELL

The nose is the sensory organ for smell.Nose can detect 20 different smells.Cells sensitive to smell is smell receptors.The smell receptors are sensitive to chemicals in the air.5. The smell receptors are located in the upper nasal cavity and covered with mucus.6. Smells are carried by certain chemicals in the air.7. When we breathe, the chemicals go through our nose.

Sensory cells( cells which are sensitive to smell)Nerve to brainAir inNasalcavitytongue

8. Nervous pathway for detecting smell.Chemicals in the air enter the nasal cavityThe chemicals will dissolve in the layer ofmoisture that covers the smell receptorson the upper part of the nose ( in mucus)The dissolved chemicals stimulate the smell receptorsThe smell receptors produce nervous impulsesThe nervous impulses are sent to the brain and thebrain identifies the smells.

Structural adaptations of noseSmell receptor are located at the upper part of the nasal cavity- enables the nose to detect most of the smells that enter the nasal cavity.The smell receptors are always covered in mucus which is secreted by the glands in the nasal cavity.When a person has a cold, he is unable to detect smells well. This is because too much mucus is being produced. The mucus prevents the chemicals from stimulating the smell receptors.

SENSE OF TASTE

The sensory organ for taste is the tongue.

Our tongue is covered by TASTE BUD which contain many TASTE RECEPTORS.

3. Sensory cells that detect taste are called TASTE RECEPTORS.

4. These receptors are found on the upper surface of the tongue.

5. Taste receptors can detect SWEET,SOUR,SALTY and BITTER tastes.

bittersaltysoursweet

TASTE 6.Sweet tastedetected by sweet receptorsSalty tastedetected by salty receptorsSour tastedetected by sour receptorsBitter tastedetected by bitter receptors

The receptors are found in different areas of the tongue and they respond to different tastes. i. Bitter taste Detect :Black coffeeBitter gourdMedicine

ii. Sour tasteDetect :AcidLime juiceVinegarTamarind sauceLemon

iii. Salty tasteDetect :SaltSea waterSoya sauceSalty fish

iv. Sweet tasteDetect :Sugar honeyIce creamChocolate

Detection of tasteSaliva dissolves the food substances in the mouth.Dissolved food substances stimulates the taste receptors in the taste buds.The taste receptors send messages to the brain in the form of nerve impulses.The brain interprets the taste of the food.

Sense of Taste and SmellBoth the senses are needed to detect the flavour of food.The nasal cavity and the mouth are connected.The chemicals from food that stimulate taste receptors will also move into nasal passage.When we have cold or close our nose, our ability to taste the food is reduced.

D. SENSE OF HEARINGThe ear is the sensory organ for hearing. The ear can detects sound. The human ear can be divided into 3 parts: outer ear middle ear inner ear

OUTER EARpinnaear canaleardrum

ossiclesoval windowMIDDLE EAREustachian tube

pinnacochleaauditory nervesINNER EARSemicircular canals

Outer earMiddle earInner earpinnapinnaear canaleardrumossiclesoval windowcochleaauditory nerves

PINNACollect sound waves. Direct the sound waves into the ear (auditory) canal

EAR CANAL ( AUDITORY CANAL)Direct the sound waves to the ear drum

EAR DRUM Vibrates when the sound waves hit it.

OSSICLES( EAR BONES ) Magnifies( amplify) the vibrations.Transfer the vibrations from eardrum to the oval window.

OVAL WINDOW As the oval window vibrates, it will transfer the vibrations from the ossicles to the cochlea.

COCHLEA Detects the vibrations. ( the fluid inside the cochlea vibrate)Converts the vibrations to nerve impulses

AUDITORY NERVE Sends the nerve impulses ( message) from the cochlea to the brain to interpret.

EUSTACHIAN TUBEBalance the air pressure on both sides of the eardrum

SEMICIRCULAR CANALControls the balance of the body

The path taken by the sound waves from the ear to the brain ( MECHANISM OF HEARING) is :PINNAEARDRUMEAR CANAL ( AUDITORY )OSSICLESOVAL WINDOWCOCHLEAAUDITORY NERVEBRAINThe EUSTACHIAN TUBE and SEMICIRCULAR CANAL are not involved in the hearing mechanism.

1234567MECHANISM OF HEARING

1. pinna2. ear canal3.eardrum4. ossicles5. oval window6. cochlea7. auditory nervesMECHANISM OF HEARING

The pinna collects sound waves. It then directs the sound waves down the ear canal. The ossicles amplify the sound vibrations and transmit them to the oval window.2.The sound waves travel along the ear canal to the eardrum. The sound waves strike the eardrum .The eardrum vibrates.The vibrations passing through the oval window causes the fluid in the cochlea to vibrate. The cochlea detects the vibrations. It converts the sound vibrations to nerve impulses.The nerve impulses are sent to the brain by auditory nerve. The brain interprets the impulses as sound.

SENSE OF SIGHT

The eye is a sensory organ of sight and responds to light.2. It is made up of three layers :sclerachoroidretina

Structure of the Human EyelensaqueoushumouririscorneapupilConjunctiva

Structure of the Human EyeretinavitreoushumourOptic nerveyellowspotblind spotSuspensary ligamentCiliary muscle

The functions of corneaHelps to focus light onthe retina

iris-Controls the size of pupil.

pupilControl the amount of Light entering the eye.

Aqueous humour Helps to focus light onthe retina.

lensFocuses light on theretina.

Vitreous humour - Helps to focus light on the retina.Helps to keep the eye ball shape.

retinaDetects light- Produce nerve impulses

Yellow spotDetects images of objects formed on it.

Optic nerveSends nerve impulses from the retina to the brain.

Blind spotThe part that is not sensitive to light.Not able to detect image.

Ciliary muscles Contracts and relaxes to change the thickness of lens.

Suspensory ligament Holds the lens in its position.

3. The parts of the eye that help to focus light onto the retina are: - the cornea - the aqueous humour - the lens - the vitreous humour.

The eye is able to focus the light from an object on the retina by changing the thickness of the lens.

corneaAqueous humourlensvitreous humour

THE SIGHT MECHANISM IN EYES.

Light is reflected off an object into our eyes.11. The light travels through the pupil and the eye lens , then the light is focused onto the retina.12. The optic nerve sends the nerve impulses from the retina to the brain.13. The brain interprets the image .14. The image formed on the retina is real, inverted and smaller than the object.

15. Formation of image on retina.objectImage: -inverted -real - smaller than object

LightPupilVitreous humourCorneaAqueous humourLensRetina

16.The formation of an image on the retina:Reflected light raysfrom an object enterthe eye.The lens focuses the light rays onto the retina.The cornea,aqueous and vitreous humour help to refract and focus the light onto the retina.A real, inverted and diminished(smaller) image is formed on the retina.The impulse produced by the retina is sent through the optic nerve to the brain.The brain interprets the image as an upright object.

Near objectLooking at near objectsThe eye lens becomes thicker

Far object

Looking at far objectsThe eye lens becomes thinner

5. IRIS control the size of the pupil6. PUPIL allows light to enter the eye.IrisPupil

7. The size of the pupil change under different situations.

8. When a person moves from a dark area into a bright area The pupil becomes smaller. Less light enters the eye.The eye is not blinded by excess light.

9. When a person moves from a bright area into a dark area . The pupil enlarges.( became large) More light enters the eye.The eye can see in the dark after a while.

Light has four important properties: a) It travels in a straight line b) It can be reflected c) It can be refracted d) It can be dispersed

Solar eclipse occurs when the moon comes between the sun and the earth, casting its shadow on the earth.

Lunar eclipse occurs when the earth comes between the sun and the moon, casting its shadow on the moon.

Reflection of lightAccording to the law of reflection a) the incident ray, reflected ray and normal are all on the same plane. b) the angle of incidence is equal to the angle of reflection

Refraction of lightRefraction of light takes place when light travels through two different media with different densities.

The speed of light changes when it moves from one medium to another with a different density which causes the light to be refracted (bent)

EYE DEFECTS

Defects of the eye take place when the image does not fall on the retina.2.The eye defects are :

short-sightedness long sightedness astigmatism

SHORT SIGHTEDNESS

1. A person can see near objects clearly. A far objects appear blurred. Image is formed in front of the retina. The defect may be caused by : eyeball is too big ( long ) lens is too thick. The defect can be corrected by : wearing concave lens.

Concave lens

LONG SIGHTEDNESS

1. A person can see far objects clearly. A near objects appear blurred. Image is formed behind the retina. The defect may be caused by : eyeball is too small ( short ) lens is too thin The defect can be corrected by : wearing convex lens.

Convex lens

ASTIGMATISM

A vision defect caused by the IRREGULAR CURVE OF THE CORNEA.2. It can be corrected by wearing glasses with cylindrical lenses or by surgery.

This happens when the cornea loses its smooth, curved shaped, causing light rays that enter the eye to fall on different spots instead of being focused to a certain spot on the retina. As a result the image is blurred.

Blindness is a condition in which the eyes cannot detect any light at all or the brain fails to receive or interpret nerve impulses from the eyes.

Colour-blindness is a condition in which the eyes cannot differentiate certain colours especially red and green.

LIMITATION OF THE SENSE OF SIGHT

OPTICAL ILLUSION

Sometimes what we see may not appear to be the real thing.2.This is cause when the brain cannot interpret accurately what is actually seen by the eye.3.This limitation of the sense is known as optical illusion.

LIMITATION OF THE SENSE OF SIGHT

BLIND SPOT

1.The blind spot is present in every eye.The blind spot does not have any receptors sensitive to light.3. It cannot detect any image that falls on it.

XNo nervereceptor

STEREOSCOPIC VISION AND MONOCULARVISION

STEREOSCOPIC VISION

STEREOSCOPIC VISION is vision involving both eyes.2. This enables us to estimate distances accurately.The stereoscopic field of vision is narrow Predators usually have stereoscopic vision.

STEREOSCOPIC VISION AND MONOCULARVISION

MONOCULAR VISION

MONOCULAR VISION is vision involving one eye only.2.They are not able to estimate distances accurately.The monocular field of vision is widePreys usually have monocular vision.

COMPARISON BETWEEN STEREOSCOPIC ANDMONOCULAR VISION.

DIFFERENCEBoth eyesThe way objects are viewedOnly one eyeLocated in front of the headPosition of the eyeLocated on the sides of the head

Narrow Field of visionWide

Overlapping Field of vision by the right and left eyes

Does not overlapCan estimate distances accuratelyEstimation of distanceCannot estimate distances accuratelyHelp them to estimate distances accurately when hunting preyImportance Help prey to detect and escape from predator

Use of optical instrument.1.Optical instrument can be used to help overcome the limitations of the sense of sight.

DeviceFunctionsMicroscopeHelps us to see fine and small objectPeriscope Used in submarines to see above the sea level.Ultrasound scannerCan produce an image of a foetus in a pregnant womans womb.X-ray machineTo observe our bodies internal organsTelescope & binocularsHelps us to see distant objects

Use of hearing aid.1. Hearing aid is used to help overcome the limitations of the sense of hearing .

Properties of sound

1. Sound a form of energy produced from vibrations travels in the form of waves can be reflected can be absorbed can only travel through a medium travels fastest through solids, followed by liquids and gases cannot pass through a vacuum

Production of sound a. Sound is produced when the ruler vibrates.

Sound is produced when a fork is struck on the surface of a table.

c. Sound is produced when the air vibrates.Sound can travel through solid, liquid and gas.Sound travels faster through solids and slowest through gas due to arrangement of the particles in solid which are closely packed and vibrate efficiently.5. Sound cannot travel through a vacuum such as explosion in space cannot be heard on Earth.

Sound cannot travel through a vacuum.

Before the air is sucked out: a. The electric bell vibrates. b. Sound is heard.

2. After the air is sucked out ( in vacuum state ) a. The electric bell still vibrates. b. Sound is not heard.

Conclusion : a. Sound needs a medium to travel. b. Sound cannot travel through a vacuum.

Properties of soundThe loudness of sound depends on how much energy it carries.The loudness of sound is measured in Decibels (dB). Slow vibrations produce low-pitch sounds (mooing of a cow). Rapid vibrations produce high-pitch sound (screaming of a baby).

The number of vibrations happening per second is called frequency. The unit of frequency is Hertz (Hz).Frequency is the pitch of sound. We hear different frequencies as different pitches.High-pitched sounds have high frequency and low-pitched sounds have low frequency.

Reflection and absorption of soundSound waves will be reflected or absorbed. Sound can be reflected when they hit hard and smooth surface like concrete, stone wall, tunnel or caves.3. The reflection of sound causes ECHO to be formed in caves or closed hall.4. The strength of an echo depends on the properties of the surface.5. Reflection of sound can be reduced by using sound absorbers.

Application of the reflection of sound : a. Determining the depth of the sea. b. Determining the presence of fish. c. Determining the presence of enemys ship5. Application of the absorption of sound : a. Wall of halls and big building have soft boards and curtain to absorb sound and reduce echo. b. Cushion and soft padding in cars absorb the noise from the engine.

Defects of hearing

Deafness is defect in the hearing mechanism.It is caused by damage to some part of the ear :The hearing defect can be corrected through surgery or by using a hearing aid.4. Damaged ossicles can be replaced.5. Torn eardrums can be patched.

When the sound vibrations reach the cochlea, they bend the tiny hairs in it. These hairs then send messages to brain.

Weak sounds cause small vibrations and bend the hairs slightly. Loud sounds cause large vibrations and cause a greater bending of the hairs. Very loud sounds damage the hairs and lead to permanent loss of hearing.

P: Ossicles R: Cochlea DeafnessQ:Eardrum S: Auditorynerve

LIMITS OF HEARING

Human beings cannot hear all frequencies of sound.Some old people cannot hear sound as well as young people because their eardrum have lost their elasticity.3. A stethoscope is used by doctors to listen the heartbeats of patients.4. A loudhailer or microphone is used to give high quality sound as well as high volume.

Cotton wool/carpet

Metal sheet : a. The ticking of the stopwatch is heard clearly

2. Conclusion : a. the metal sheet is a good sound reflector b. a hard and smooth surface reflects sound.Cotton wool/carpet wall: a. The ticking of the stopwatch is not heard clearly

2. Conclusion : a. the cotton wool is a good sound absorber. b. a soft and porous surface absorbs sound.

Sonar is used in marine to detect the high frequency sounds produced by their enemies.6. Sonar also used by the fishermen to detect the presence of fish.

STEREOPHONIC HEARING

Stereophonic hearing involves the use of two ears.A sound coming from the right will be detected by our right ear earlier than left ear and its will produce stronger vibrations.3. Stereophonic hearing enables us to determine the direction of the sound.

STIMULI AND RESPONSE IN PLANTS

Plants can detect and respond to stimuli around them. 2. Plants respond to stimuli in two ways : a: tropism b: nastic movements3. There are two types of tropisms: i. Positive tropism : movement or growth towards the stimuli. ii. Negative tropism : movement or growth away from the stimuli.Tropisms are responses to stimuli which come from one direction. The movement are slowly.

5. Types of tropisms and their stimuli :

TROPISMSSTIMULUSRESPONSEFUNCTIONSLIGHTPHOTOTROPISM- To obtain sunlightGRAVITYGEOTROPISMTo obtain water and mineral salts To roots itself firmly in the soil.WATERHYDROTROPISM- To obtain water and mineral salts.TOUCHTHIGMOTROPISM- To obtain support and sunlight.

TROPISM IN PLANTSAfter one week :The shoots respond to ________, the growth of shoot shows POSITIVE PHOTOTROPISM.2. The roots respond to _________, the growth of roots shows POSITIVE HYDROTROPISM

TROPISM IN PLANTSAfter one week :The shoots respond to ________, the shoots grow upwards, showing NEGATIVE GEOTROPISM.2. The roots respond to _________ the roots grow downwards, showing POSITIVE GEOTROPISM.

THIGMOTROPISMS

ThigmotropismGrowth of plant organs in response to physical contact.When a tendril of these climbing plants touches a supporting structure, it curves towards the support and coils around it.This allows the climbing plants to grow upright and reach sufficient height to gain enough light for photosynthesis.

NASTIC MOVEMENT

Nastic movement are responses to stimuli which come from any direction. These responses do not depend on the direction of stimuli.2. Example : i. Mimosa pudica ii. Venus fly trap iii. Pitcher plant ( Monkey pot plant )

Thermonasty ( opening of tulip flowers in response to a rise in temperature).Photonasty (opening of evening primrose flowers at night in response to the available amount of light).Seismonasty (the folding up and drooping of leaves of the Touch-Me-Not plant (Mimosa pudica) in response to touch.

Nyctinasty (response to changes in light and temperature occurring between the day and night).Seismonasty help plants like Mimosa pudica to protect its leaves from damage.Venus flytrap get nutrition by trapping insects in its specially modified leaves.

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