Class 10 Biology Chapter 3 Notes Kerala Syllabus Behind Sensations Questions and Answers

A thorough understanding of SCERT Kerala Syllabus 10th Standard Biology Notes Pdf and Class 10 Biology Chapter 3 Behind Sensations Notes Questions and Answers English Medium can improve academic performance.

SSLC Biology Chapter 3 Notes Questions and Answers Pdf Behind Sensations

SCERT Class 10 Biology Chapter 3 Behind Sensations Notes Pdf

SSLC Biology Chapter 3 Questions and Answers – Let Us Assess

Question 1.
Which of the following statements is correct?
a. Each taste bud has different chemoreceptors.
b. Opsin in rhodopsin contains retinal which is formed from vitamin A.
c. Photoreceptors are formed from optic nerve.
d. Both rhodopsin and photopsin contain retinal.
Answer:
b. Opsin in rhodopsin contains retinal which is formed from vitamin A., d. Both rhodopsin and photopsin contain retinal.

Question 2.
Recreate the illustration as given below by including any sense organ.
Answer:

(a) Eye (sense organ) – Light (stimulus) – Photoreceptors in retina (receptors) – Stimulate rhodopsin/photopsin – Impulse – Optic nerve (nerve) – Visual cortex in the brain (centre in the brain) – Vision (sensation)
OR
(b) Sound waves (stimulus) – Auditory receptors in the cochlea (receptors) – Stimulate hair cells in the Organ of Corti – Impulse – Auditory nerve (nerve) -Auditory centre in the temporal lobe of the brain (centre in the brain) – Hearing (sensation)

Question 3.
Listen to the conversation between two children. Evaluate it and record your opinion.
Child 1 – We should be proud of being born as humans. Humans have the most developed and efficient brain and sense organs.
Child 2 – It is enough to talk about the brain, as the sense organs are its continuation.
Answer:
The sense organs collect information from the surroundings and send it to the brain. The brain then interprets and coordinates responses. So, both statements are partly correct. Sense organs and brain work together, but sense organs are not merely extensions – they are specialized to detect specific stimuli.

Question 4.
Analyse the information given in the columns A, B, C. If inter connected information is present in three columns. Rearrange them suitably.

Answer:
Cochlea – Organ of Corti – Auditory receptors
Tympanum – Ear ossicles – Oval window
Vestibule receptors – Nerve fibres – Cerebellum
Outer ear – Perilymph – Endolymph

Question 5.
Correct the mistake, if any.
Impulses are formed in the retina due to the dissociation of rod cells.
Answer:
Impulses are formed due to the dissociation of rhodopsin in rod cells, not the cells themselves.

Question 6.
Analyse the given word pairs below, and find the relationship between them.
Retinal – Night blindness
Umami – Taste buds
Cone cells – Colour Blindness
Answer:
Retinal – Night Blindness
Relationship : Vitamin Deficiency/Dysfunction
Retinal is a form of Vitamin A, essential for the functioning of rod cells in the retina. A deficiency of Vitamin A (retinal) can lead to night blindness, where a person can’t see well in dim light.

Umami – Taste Buds
Relationship : Stimulus – Receptor
Umami is one of the five basic tastes (along with sweet, salty, bitter, and sour pungent). Taste buds are the receptors that detect umami flavor, especially through glutamate compounds.

Cone cells – Colour Blindness
Relationship : Cell type – Disorder due to malfunction
Cone cells in the retina are responsible for colour vision. If cone cells are absent or nonfunctional, it can lead to colour blindness.

Question 7.
Classify the given activities based on the indicators.
• The image of your friend formed in the retina
• Looking at the friend and smiling
• The impulses of the image formed on the retina is sent to the brain.
• Photoreceptors are stimulated

Indicators
• Activity/activities related to sensory nerve fibres
• Activity/activities related to motor nerve fibres
• The activities not related to the above ones
Answer:
• Activity/activities related to sensory nerve fibres
The impulses of the image formed on the retina is sent to the brain.

Photoreceptors are stimulated
• Activity/activities related to motor nerve fibres
Looking at the friend and smiling
• The activities not related to the above ones
The image of your friend formed in the retina

Question 8.
Which part of the eye helps in focusing the light towards the retina
(a) Cornea
(b) Pupil
(c) Lens
(d) Iris
Answer:
(c) Lens

Question 9.
What is the main function of a neuron?
(a) Protects organs
(b) Exchange electric signals
(c) Filters blood
(d) Produce retinalin
Answer:
(b) Exchange electric signals

Question 10.
How does the arrangement of rod cells and cone cells in the retina affect our ability to see in different conditions of light? Why does this adaptation become beneficial evolutionary?
Answer:
The retina in the human eye contains two types of photoreceptor cells: rod cells and cone cells. These cells are crucial for how we see in different lighting conditions, and their arrangement helps us to function effectively both during the day and at night.

Rod Cells
Function: Rod cells are responsible for seeing in dim light or night vision.
Location: These cells are found mainly in the outer regions (periphery) of the retina.
Sensitivity: Rod cells are highly sensitive to light, but they do not detect color.
Advantage: Rod cells allow us to see in low-light conditions but only in shades of black, white, and gray (no color vision).

Cone Cells
Function: Cone cells are responsible for color vision and sharp, detailed vision.
Location: Cone cells are concentrated in the center of the retina, especially in the region that provides the sharpest vision.
Sensitivity: Cone cells are less sensitive to light but are active under bright light (daylight).
Advantage: Cone cells help us see in full color and perceive fine details during the day.

How the Arrangement Affects Vision:
In Dim Light (Night Vision): Rod cells become active, allowing us to see in low light, but without color or high detail.
In Bright Light (Day Vision): Cone cells take over, allowing us to see in color and perceive high details.

This adaptation is evolutionarily beneficial because:
Survival in Different Light Conditions: Rod cells are important for seeing at night or in dim light, which would have helped early humans to detect danger or prey in low-light environments. Cone cells are useful for seeing clearly during the day, which is helpful for activities like identifying ripe fruits, spotting animals, and reading environmental cues in daylight.

Better Vision for Different Activities: By having both rod and cone cells, humans can see in both low light and bright daylight, allowing us to perform a wide range of activities like hunting or gathering food, and also recognizing the surroundings.

Adaptation to Daytime Life: Since humans are diurnal (active during the day), the presence of cone cells allows us to have detailed vision in daylight. The rod cells are a leftover adaptation from ancestors who were more active in dawn or dusk, where light levels were lower.

Question 11.
How does the structure of the ear enable it to convert the sound waves into signals that the brain can interpret? How do damages in different parts of the ear affect hearing and balance?
Answer:
The ear is an essential organ for hearing and balance, and its structure helps in converting sound waves into signals that the brain can understand. The ear is divided into three parts: the outer ear, middle ear, and inner ear. Sound waves are first collected by the outer ear and directed through the ear canal to the eardrum. The eardrum vibrates when sound waves hit it, and these vibrations are passed on to three small bones in the middle ear, called ossicles. The ossicles amplify the sound vibrations and send them to the oval window of the inner ear.

In the inner ear, the vibrations are transferred to the cochlea, a spiral-shaped structure filled with fluid. The fluid inside the cochlea moves, causing hair cells to bend. These hair cells convert the mechanical vibrations into electrical signals, which are then sent to the brain through the auditory nerve, where the brain interprets them as sound. The inner ear also contains the vestibular system, which helps maintain balance.

Damage to different parts of the ear can affect hearing and balance in different ways. Damage to the outer ear or middle ear usually causes conductive hearing loss, where sound is not properly transmitted to the inner ear. This can happen due to infections, blockages, or injury. Damage to the inner ear or the auditory nerve can cause sensorineural hearing loss, where the brain cannot receive proper signals from the cochlea. This type of damage can also affect balance, leading to dizziness or vertigo, since the vestibular system in the inner ear controls balance.

Biology Class 10 Chapter 3 Notes Kerala Syllabus Behind Sensations

Question 1.
The completed table 3.1 of page 73

Answer:

Reasons	Responses
Seeing a friend	Smiling or waving
Seeing a bright light	Closing or covering the eyes
Hearing a loud sound	Covering the ear
Touching something hot	Pulling the hand away
Smelling tasty food	Mouth watering
Feeling thirsty	Drinking water

Question 2.
Analyse the given hints and draw inferences regarding the diversity of stimuli, page 73
Answer:

Situations / Hints	Type of Stimulus	Inference
Takes food when hungry	Internal stimulus (hunger)	The body responds to internal needs like hunger by initiating eating behavior.
A rabbit, upon seeing a lion, gets scared and runs away	Visual stimulus (sight of predator)	Animals respond to dangers in their surroundings through fear and escape.
Blanketing to keep out cold	Temperature stimulus (cold)	Organisms detect and react to changes in temperature to maintain body heat.
Holding an umbrella to keep out the rain	Environmental stimulus (rain)	Human behavior adjusts to environmental conditions like rain for protection.
Body temperature increases during certain diseases	Internal stimulus (infection)	The body reacts internally through mechanisms like fever during illness.

Question 3.
The completed table 3.2 of page 75

Answer:

Sense Organs	Receptors	Stimulus
Eye	Photoreceptors	Light
Ear	Auditory receptors	Sound
Nose	Olfactory receptors	Smell
Tongue	Chemoreceptors	Taste
Skin	Touch receptors	Touch, pressure, temperature

Answer of Indicators of page 76
Question 4.
Position of the eye
Answer:
Human eyes are located in sockets (orbits) in the front part of the skull. Eyes are placed in the front of the face, side by side.

Question 5.
Function of eye muscles
Answer:
Eye muscles help move the eyeball in different directions – up, down, left, right, and diagonally. They allow us to quickly shift focus and track moving objects.

Question 6.
Importance of the eyelid, eyelashes, etc.
Answer:
Importance of Eyelids – Eyelids protect the eyes from dust, bright light, and injury. They also help spread tears to keep the eyes moist.

Importance of Eyelashes – Eyelashes act like filters, preventing dust, insects, and small particles from entering the eyes. They also trigger a blink reflex when something comes too close.

Question 7.
Importance of conjunctiva, tears
Answer:
Conjunctiva is the membrane that covers the anterior part of the eye, including the eyelids except the cornea. Its functions are to protect the eye, keep it moist and lubricated, and prevent dust, germs and other particles from entering the eye.

Tears are produced by the lacrimal glands. These glands are present in the eyelids towards the upper part, fears are essential for keeping the surface of the eye moist, providing nutrients and eliminating waste materials. The enzymes called lysozyme present in tears help to protect from infections.

Question 8.
Make a table by comparing the aqueous humor with the vitreous humor.
Answer:

Feature	Aqueous Humor	Vitreous Humor
Location	Between the cornea and lens	Between the lens and retina
Appearance	Watery fluid	Transparent, jelly – like
Function	Regulates pressure in the aqueous chamber Provides oxygen and nutrients to lens and cornea	Maintains the shape of the eyeball.

Question 9.
Completed flowchart 3.1 page 78

Answer:
Layers of the eye
Sclera (outer layer) – provides firmness and protection to the eye
Choroid (middle layer) – Provides oxygen and nutrients to the inner layer of retina and regulates temperature.
Retina (inner layer) – Contains photoreceptor cells. The image is formed.

Question 10.
Completed flowchart 3.2 page 80

Answer:
Cornea – Aqueous Humor – Pupil – Lens – Vitreous Humor – Retina

Answers of Indicators of page 80

Question 11.
Muscles associated with the pupil
Answer:
Radial muscles, Circular muscles and Ciliary muscles

Question 12.
Muscular activity and difference in the size of the pupil.
Answer:
The size of the pupil is regulated by the radial muscles and circular muscles seen in the iris. The size of the pupil has to be regulated in order to see the objects clearly in dim light and to prevent damage to the retina in intense light. During dim light, radial muscle contracts and the size of pupil increases. During intense light, circular muscle con-tracts and the size of pupil decreases.

Question 13.
The completed illustration 3.4. page 82 – The change in the activities of these parts of the eye while viewing near objects and distant object.

Answer:

Answers of Indicators of page 83

Question 14.
Photoreceptors – Shape, number
Answer:
Rod cells are cylindrical and cone cells are cone shaped. Rod cells are about more than 9 crores in number and cone cells are about 45 lakhs.

Question 15.
Photoreceptors – Pigments and its components
Answer:
Rod cells contain the pigment called rhodopsin and in cone cells is photopsin. The components of both pigments include a protein namely opsin and retinal, formed from Vitamin A. However, the chemical structure of retinal is different in rhodopsin and photopsin.

Question 16.
What is the importance of pigments in photoreceptors?
Answer:
Photoreceptors are special cells in the retina of the eye that help us see. They contain light-sensitive pigments that absorb light and start a chemical reaction. This reaction produces nerve signals, which are sent to the brain through the optic nerve. These pigments are very important because they allow us to detect light, color, and movement. Without them, we wouldn’t be able to see in bright or dim light.

Analysing flow chart 3.3 of page 83 and Answers of indicators of page 84
Question 17.
Stimulation of photoreceptor cells
Answer:
Glutamate acts as the primary neurotransmitter in photoreceptors. Variations in glutamate production are responsible for the perception of darkness and light.

Question 18.
Synthesis of glutamate and bipolar cells
Answer:
In the dark, photoreceptors continuously produce glutamate. On bipolar cells (those that sense light) are inactivated and off bipolar cells (those that sense darkness) are activated. Off bipolar cells that indicate the absence of light form impulses that reach the brain through the optic nerve, creating a sense of darkness.

In the presence of light, photorecptors do not produce glutamate. On bipolar cells become active and off bipolar cells become inactive. On bipolar cells that indicate the presence of light form impulses that reach the brain through the optic nerve, creating a sense of vision.

Question 19.
Ganglion cells and impulses
Answer:
Ganglion cell layer – Transmits impulses from bipolar cells to the optic nerve

Question 20.
Is retina necessary to see black colour?
Answer:
Yes, the retina is necessary to see black colour, just like it is for seeing any other colour or image. The retina is a light – sensitive layer at the back of the eye that contains photoreceptor cells (rods and cones). These cells detect light and send signals to the brain, allowing us to see. Rods in the retina are especially sensitive to light and help us see in dim light or detect shades like black, white, and grey. When an object appears black, it means it absorbs all light and reflects none. The absence of reflected light is detected by the retina (mostly by rods), and the brain interprets this as black. So, without the retina, the eye wouldn’t be able to detect any colour – including black.

Question 21.
Can you find out the reason for colour blindness?
Answer:
Yes, colour blindness is usually caused by a problem in the genes that produce pigments in the cone cells of the eye. These cone cells help us see different colours – red, green, and blue. The genes responsible for red and green cone pigments are located on the X chromosome. The gene for blue cone pigment is located on chromosome 7. Since males have only one X chromosome (XY), if they inherit a defective gene for red or green pigment on the X chromosome, they do not have another X to compensate. This is why colourblindness is more common in males. If the cone cells don’t produce the right pigments, the brain receives incorrect signals, leading to difficulty in distinguishing certain colours – usually red and green.

Answers of indicators of page 85
Question 22.
Why are men more affected by colour blindness?
Answer:
The gene responsible for the production of pigments in cone cells which are sensitive to green and red are found in the X chromosome.

Question 23.
The possibility of colour blindness in women
Answer:
Colour blindness is a condition where a person has difficulty seeing certain colours, usually red and green. It is more common in men but rare in women. This is because the gene responsible for colour blindness is found on the X chromosome. Since women have two X chromosomes, even if one X carries the faulty gene, the other normal X can compensate. Therefore, women usually become carriers but do not show the condition unless both X chromosomes carry the faulty gene – which is very rare.

Question 24.
The mode of inheritance of colour blindness
Answer:
Colour blindness is inherited as a sex-linked recessive trait. The gene for it is located on the X chromosome. Males have only one X chromosome (XY), so if they inherit the defective gene from their mother, they will be colour blind. Females have two X chromosomes (XX), so they need to inherit the defective gene from both parents to be colour blind. If they get only one defective gene, they become carriers but do not show symptoms.

Question 25.
Completed table 3.4 of page 86

Answer:

Eye Diseases / Disorders	Reason	Treatment
Short-sightedness	Enlarged eyeball	Spectacles with concave lens, contact lens, or surgery
Long sightedness	Eyeball is too short or lens is less curved	Spectacles with convex lens, contact lens, or surgery
Astigmatism	Irregular curvature of cornea or lens	Spectacles with cylindrical lens
Cataract	Eye lens becomes opaque	Surgical removal and replacement with artificial lens
Glaucoma	Failure in the reabsorption of aqueous humor, pressure increases and the optic nerve gets damaged	Eye drops, medication, laser treatment
Conjunctivitis	Infection in the conjunctiva (bacterial or viral)	Antibiotic/antiviral eye drops and maintaining eye hygiene
Diabetic retinopathy	Damage to retina due to uncontrolled diabetes	Managing diabetes, laser treatment, or surgery
Night blindness	Deficiency of Vitamin A	Vitamin A supplements, diet rich in Vitamin A
Xerophthalmia	Prolonged Vitamin A deficiency causing corneal dryness and damage	Vitamin A therapy and improved nutrition

Question 26.
Completed table 3.5 of page 90

Answer:

Main parts of the ear	Associated parts
Outer ear	Pinna, Auditory canal, Tympanum
Middle ear	Ear oscicles, Eustachian canal
Inner ear	Vestibule, Cochlea, Vestibular nerve, Auditory nerve

Question 27.
Completed flowchart 3.5 of page 93

Answer:

Question 28.
Completed table 3.6 of page 93.

Answer:

Part	Function
Pinna	Directs the sound waves into the auditory Canal. Helps to identify the direction from which sound is produced. Protects the auditory canal to some extent from foreign particles.
Auditory Canal	Directs sound waves to the tympanum. Protects the tympanum from foreign particles. Hair, earwax, and sebum prevent dust and germs from entering; earwax has disinfectant properties.
Tympanum	Vibrates in accordance with sound waves. Transfers vibrations to the ear ossicles.
Ear Ossicles	Vibrate as a result of tympanum vibrations. Transfer these vibrations to the oval window.
Oval Window	Receives vibrations from the ear ossicles – Transfers vibrations to the cochlea.
Cochlea	Contains three chambers (upper and lower filled with perilymph, middle with endolymph). Converts vibrations into impulses via the Organ of Corti.
Organ of Corti	Contains auditory receptors (hair cells) that generate impulses in response to vibrations.
Auditory Nerve	Carries impulses from the Organ of Corti to the brain resulting in the sense of hearing.

Answers of Indicators of page 94
Question 29.
The parts of inner ear associated with balance.
Answer:
The part of the inner ear that maintains body balance is the vestibular system, which includes three semicircular canals, vestibule and hair cells.

Question 30.
Position of the hair cells
Answer:
In the three semicircular canals. The utricle and saccule of the chamber called the vestibule also contain hair cells.

Question 31.
Fluid in the chambers
Answer:
The upper and lower chambers of cochlea are filled with a fluid called perilymph. The middle chamber is filled with endolymph.

Question 32.
The situation in which hair cells are stimulated
Answer:
The linear movement of the head generates impulses in these hair cells.The endolymph present in the canals, which are arranged perpendicular to each other, moves with the rotational movement of the head. As a result of this movement, the hair cells present here get stimulated and impulses are formed. The utricle and saccule of the chamber called the vestibule also contain hair cells. The linear movement of the head generates impulses in these hair cells.

Question 33.
The part of the brain associated with balance is cerebellum
Answer:

Question 34.
Completed flowchart 3.5 of page 96

Answer:

Answers of Indicators of page 97
Question 35.
Papilla in the tongue
Answer:
The papillae are structures on the tongue that have minute pores through which saliva enters and interacts with taste molecules.

Question 36.
Position of taste buds
Answer:
Taste buds are located within the papillae of the tongue.

Question 37.
Chemoreceptors and taste
Answer:
A taste bud will have about 100 chemoreceptors. Microvilli from each chemoreceptor, reach the minute pores present in the papilla. Saliva enters through this pore. Substances that give rise to taste are dissolved in saliva and stimulate chemoreceptors.

Question 38.
Saliva and the sense of taste
Answer:
A taste bud will have about 100 chemoreceptors. Microvilli from each chemoreceptor, reach the minute pores present in the papilla. Saliva enters through this pore. Substances that give rise to taste are dissolved in saliva and stimulate chemoreceptors. The impulses produced by these molecules in the chemoreceptors reach the brain through the nerve and make the sense of taste. The main tastes we recognise are sweet, sour, salty, pungent, bitter and umami.

Question 39.
Completed table 3.7 of page 98

Answer:

Process	Smell	Taste
The fluid in which substances dissolve	Mucus	Saliva
Stimulated receptor	Olfactory receptor	Chemo receptor
The nerve that carries impulses to the brain	Olfactory nerve	Respective nerve

Std 10 Biology Chapter 3 Notes – Extended Activities

Question 1.
In a dark room, gradually increase the amount of light using a flash light or dimmer. Observe how different light levels affect the ability to see colours and details, and record record your findings.

Question 2.
Rotate slowly in a circle and try to walk in a straight line to observe how this activity affects your balance and hearing. Record your inferences.

Question 3.
Make a simple 3D model of the eye using craft materials (clay, paper, markers) to represent parts such as cornea, lens, retina, optic nerve etc.

Question 4.
Set up a few soundzones around the classroom with different sound sources (tapping, clapping, ringing). Each students is blind folded and made to move between the stations. Identify the direction and type of sound. Observe how the structure of the ear helps detect sounds.

Behind Sensations Class 10 Notes

Behind Sensations Notes Pdf

• Responses are formed due to various biological and chemical processes that takes place in the body of organisms.
• Stimuli are the circumstances that lead to responses in living beings.
• Stimuli are recognised by the body through specialised cells or nerve endings known as Sensory Receptors.
• Electrical impulses are produced in receptors in response to external and internal stimuli. These impulses are known as receptor potential.
• Action potential travels through neuron as nerve impulses.
• Senses that can be recognised through receptors are divided into two types: general senses and special senses.
• The eye is an important sense organ that provides perception about the external world.
• Conjunctiva is the membrane that covers the anterior part of the eye, including the eyelids except the
  cornea.
• Tears are produced by the lacrimal glands. These glands are present in the eyelids towards the upper part.
• The enzymes called lysozyme present in tears help to protect from infections.
• Sclera (outer layer) provides firmness and protection to the eye.
• Cornea – The transparent anterior part of the eye, allows light to enter the eye.
• Choroid (middle layer) provides oxygen and nutrients to the inner layer of retina and regulates temperature.
• Ciliary muscles Adjusts the curvature of the lens
• Iris – Two types of muscles in the iris regulate the size of the pupil depending on the intensity of light.
• Convex lens – forms a small, real and inverted image of the object on the retina.
• Retina has Layer of photoreceptors, Bipolar cell layer, Ganglion cell layer
• Layer of photoreceptors – The photoreceptor cells called rod cells recognise objects in both dim light and in shades of black and white.
• There are no photoreceptor cells in the retina where the optic nerve originates.
• The yellow spot (macula) is seen in the middle of the retina where cone cells are abundant.
• The eye has two chambers – aqueous chamber and vitreous chamber
• The size of the pupil has to be regulated in order to see the objects clearly in dim light and to prevent
  damage to the retina in intense light.
• The lens has three main parts. They are an elastic membrane called the capsule, within which are the
  lens fibres and the epithelium, which is located solely in the anterior part, between the lens fibres and the capsule.
• The ability of the eye to foucs images of both near and distant objects accurately on the retina is called the power of accommodation.
• Rod cells contain the pigment called rhodopsin and in cone cells is photopsin.
• Glutamate acts as the primary neurotransmitter in photoreceptors. Variations in glutamate production are responsible for the perception of darkness and light.
• In the retina, there are three types of cone cells recognise primary colours.
• The gene responsible for the production of pigments in cone cells which are sensitive to green and red are found in the X chromosome.
• The gene which is responsible for the production of blue cone pigment is found in chromosome 7.
• Impulses related to the image formed in both eyes reach the visual centre of the brain through the optic nerve.
• Since each eye receives light from different angles, there will be two slightly different images on the retina. These two images are sent to the visual cortex in the brain. The brain compares these images and combines them(fusion). This process is known as binocular fusion.
• World Sight Day is observed on the second Thursday of October.
• Donating eyes can give vision to two blind people.
• Hearing is the combined experience of the ears and the brain.
• The human ear also plays a major role in maintaining the balance of the body.
• The hair inside the auditory canal, earwax and sebum secreted by glands in its wall help to prevent dust and germs from entering the ear.
• The tympanum vibrates in accordance with the sound waves. These vibrations make the bones in the ear ossicles vibrate as well.
• Eustachian canal helps to balance the pressure on both sides (middle ear and the atmospheric air in the outer ear) of the tympanum. It also facilitates the flow of mucus and fluids from middle ear to the pharynx.
• The cochlea, having the shape of a snail shell, has three chambers, oval window is the membrane that covers the opening towards the upper chamber.
• The part of the inner ear that maintains body balance is the vestibular system, which includes three semicircular canals, vestibule and hair cells.
• Hearing of loud noise (above 85 decibel) for a short time and less noise with a lesser intensity (below 55 decibel) for a very very long time can cause permanent hearing impairment.
• The tongue and nose are two interconnected sense organs.
• One can identify the smell of the food even before tasting it.
• Taste buds play a crucial role in enjoing the food by helping us to perceive the natural flavours of food.
• Amoeba/Bacteria – Detects the presence of chemicals in the surroundings and move against them.
• Euglena – The eyespot (stigma) helps to detect light and move towards it.
• Insects – The compound eye made up of Ommatidia. The Antenna helps to detect smell and touch.
• Bat – Ears and special type of echo location organ helps in hunting and travelling.
• Hawk – Eyes with high vision, systems for long distance vision and detecting ultra violet radiation.
• Snake – Jacobson’s organ helps to detect smell.
• Dog – Highly sensitive olfactory receptors (300 million) are found.
• Human senses are the powerful tools that connect us to the world around us.

INTRODUCTION

Receptors and Impulses
Responses are formed due to various biological and chemical processes that takes place in the body of organisms. Stimuli are the circumstances that lead to responses in living beings. Stimuli are recognised by the body through specialised cells or nerve endings known as Sensory Receptors. The receptors in skin, muscles, joints, internal organs and blood vessels help to detect general senses such as touch, pain, heat, pressure etc. The receptors concentrated only in certain organs help to recognise specific senses such as vision, hearing, taste and smell, etc

Eye
The eye is an important sense organ that provides perception about the external world. Conjunctiva is the membrane that covers the anterior part of the eye, including the eyelids except the cornea. Tears are produced by the lacrimal glands. These glands are present in the eyelids towards the upper part. World Sight Day is observed on the second Thursday of October. The World Health Organisation (WHO) and the International Agency for the Prevention of Blindness (IAPB) call for the observance of this day to raise awareness on the eye healthcare. WHO eyes, a free application available in 14 languages enables free eye test for ages 8 and above. Donating eyes can give vision to two blind people. Each one of us has a responsibility to adopt a careful life style to care for the eyes and to develop a positive attitude towards eye donation.

Ear
Hearing is the combined experience of the ears and the brain. The human ear also plays a major role in maintaining the balance of the body. Sound waves vibrate the tympanum. From there the vibration passes through the ear ossicles and then vibrates the oval window. The structure of the oval window is also similar to that of the tympanum. The cochlea, having the shape of a snail shell, has three chambers, oval window is the membrane that covers the opening towards the upper chamber. The upper and lower chambers of cochlea are filled with a fluid called perilymph. The middle chamber is filled with endolymph. The Organ of Corti where the auditory receptors are present is situated in the basilar membrane between middle and lower chambers of cochlea. The vibrations that reach the hair cells present here generate impulses. These impulses reach the brain through auditory nerve resulting in the sense of hearing.

The part of the inner ear that maintains body balance is the vestibular system, which includes three semicircular canals, vestibule and hair cells. The endolymph present in the canals, which are arranged perpendicular to each other, moves with the rotational movement of the head. As a result of this movement, the hair cells present here get stimulated and impulses are formed. The utricle and saccule of the chamber called the vestibule also con-tain hair cells. The linear movement of the head generates impulses in these hair cells. When the impulses reach the brain through the vestibular nerve, the brain maintains body balance by receiving impulses from the eyes and muscles as well.

Hearing impairments occur due to many reasons. Intensity of noise above 80 decibels is extremely annoying. Noise pollution is a danger that is most harmful and unfortunately, the most neglected of all the environment pollutions that we face today.

Nose, Tongue, Skin
The tongue and nose are two interconnected sense organs. While breathing, the particles responsible for smell enter the nasal cavity. Then it gets dissolved in the mucus produced by mucus membrane. Millions of olfactory neurons in the mucus membrane get stimulated by special olfactory particles. Receptors generate impulses, and they travel through the olfactory nerve to reach the part of the brain recognising smell, and the sense of smell is effected.

One can identify the smell of the food even before tasting it. Taste buds play a crucial role in enjoing the food by helping us to perceive the natural flavours of food. Food made with natural ingredients is safe and healthy rather than the taste of artificial additives or harmful substances. A taste bud will have about 100 chemoreceptors. Microvilli from each chemoreceptor, reach the minute pores present in the papilla. Saliva enters through this pore. Substances that give rise to taste are dissolved in saliva and stimulate chemoreceptors. The impulses produced by these molecules in the chemoreceptors reach the brain through the nerve and make the sense of taste. The main tastes we recognise are sweet, sour, salty, pungent, bitter and umami.

Receptors in the skin – Pain, temperature fluctuations, Touch, pressure and movement of hairs – Shape, quantity and structure of objects – Cold, touch – Intense touch, pressure, heat – Helps to find out the movement of hair – Vibration, touch with high frequency.

Sensory diversity in organisms
Amoeba/Bacteria – Detects the presence of chemicals in the surroundings and move against them. Euglena – The eyespot (stigma) helps to detect light and move towards it. Insects – The compound eye made up of Ommatidia. The Antenna helps to detect smell and touch. Bat – Ears and special type of echo location organ helps in hunting and travelling. Hawk – Eyes with high vision, systems for long distance vision and detecting ultra violet radiation.Snake – Jacobson’s organ helps to detect smell. Dog – Highly sensitive olfactory receptors (300 million) are found. Human senses are the powerful tools that connect us to the world around us.

Stimuli and Responses

• Responses are formed due to various biological and chemical processes that takes place in the body of organisms.
• Stimuli are the circumstances that lead to responses in living beings.
• Stimuli can be divided into external stimuli and internal stimuli.
• Receptors and Impulses

• Stimuli are recognised by the body through specialised cells or nerve endings known as Sensory Receptors.
• Electrical impulses are produced in receptors in response to external and internal stimuli. These impulses are known as receptor potential.
• When electrical impulses are in higher concentration, action potential is formed in the neurons associated with receptors.
• Action potential travels through neuron as nerve impulses.
• Nerve impulses reach the related parts of the brain and form appropriate response instructions. Muscles and glands respond to these instructions accordingly.

Sensory receptors and Senses

• Senses that can be recognised through receptors are divided into two types: general senses and special senses.
• The receptors in skin, muscles, joints, internal organs and blood vessels help to detect general senses such as touch, pain, heat, pressure etc.
• The receptors concentrated only in certain organs help to recognise specific senses such as vision, hearing, taste and smell, etc Position and parts related to the eye.
• The eye is an important sense organ that provides perception about the external world.

• Conjunctiva is the membrane that covers the anterior part of the eye, including the eyelids except the cornea.
• Functions of conjunctiva are to protect the eye, keep it moist and lubricated, and prevent dust, germs and other particles from entering the eye.

• Tears are produced by the lacrimal glands. These glands are present in the eyelids towards the upper part.
• Tears are essential for keeping the surface of the eye moist, providing nutrients and eliminating waste materials.
• The enzymes called lysozyme present in tears help to protect from infections.

Layers of the Eye and Associated Parts

• Sclera (outer layer) provides firmness and protection to the eye.
• Cornea – The transparent anterior part of the eye, allows light to enter the eye.
• Choroid (middle layer) provides oxygen and nutrients to the inner layer of retina and regulates temperature.
• Ciliary muscles-Adjusts the curvature of the lens
• Iris – Two types of muscles in the iris regulate the size of the pupil depending on the intensity of light.
  • Iris contains the pigment called melanin.
  • Melanin gives the iris its characteristic colour as well as absorbs ultraviolet rays.
  • Iris regulates the amount of light.
• Convex lens – forms a small, real and inverted image of the object on the retina.
• Retina (inner layer) contains photoreceptor cells. The image is formed.
• Retina has Layer of photoreceptors, Bipolar cell layer, Ganglion cell layer
• Layer of photoreceptors – The photoreceptor cells called rod cells recognise objects in both dim light and in shades of black and white.
• The cone cells provide vision in intense light and also help in recognising colours.
• Bipolar cell layer – Transmits impulses from the photoreceptors to ganglion cells.
• Ganglion cell layer – Transmits impulses from bipolar cells to the optic nerve.
• The bipolar cell layer consists of two types of cells, namely on bipolar cells and off bipolar cells.
• There are no photoreceptor cells in the retina where the optic nerve originates. This part having no vision is known as the blind spot.
• The yellow spot (macula) is seen in the middle of the retina where cone cells are abundant.
• Eye chambers and Humors

• The eye has two chambers – aqueous chamber and vitreous chamber
• The aqueous chamber is seen between the cornea and lens. The watery aqueous humor is present here.
• Aqueous humor oozes out from the blood like tissue fluid and is reabsorbed into the blood . This is how the pressure in aqueous chamber is regulated.
• Lens and cornea get oxygen and nutrients from aqueous humor.
• The vitreous chamber lies in between the lens and the retina.
• The transparent jelly like vitreous humor present there maintains the shape of the eyeball.
• Iris is the part seen behind the cornea.
• The pupil is the aperture seen at the centre of the iris. The normal size of the pupil is from 2 to 3 mm.
• When the size of the pupil increases, it becomes possible to direct 16 times more light on to the retina than normal.
• The size of the pupil is regulated by the radial muscles and circular muscles seen in the iris.
• The size of the pupil has to be regulated in order to see the objects clearly in dim light and to prevent damage to the retina in intense light.
• The lens has three main parts. They are an elastic membrane called the capsule, within which are the lens fibres and the epithelium, which is located solely in the anterior part, between the lens fibres and the capsule.
• It is the epithelium that continuously produces lens fibres throughout an individual’s lifetime.
• The main structural component of the lens is a protein called crystallin.
• The lens derives nutrients from the aqueous humour.
• Age-related changes affect the flexibility and transparency of the lens as well as vision.
• The ability of the eye to foucs images of both near and distant objects accurately on the retina is called the power of accommodation.
• Power of accommodation is achieved by changing curvature of the lens, by the actions of the ciliary muscles.

Retina

• The rod cells and the cone cells are the photoreceptors.
• Rod cells are cylindrical and cone cells are cone shaped .
• Rod cells are about more than 9 crores in number and cone cells are about 45 lakhs.
• Rod cells contain the pigment called rhodopsin and in cone cells is photopsin.
• The components of both pigments include a protein namely opsin and retinal, formed from Vitamin A.
• The chemical structure of retinal is different in rhodopsin and photopsin.

Photoreceptors to the brain

• Glutamate acts as the primary neurotransmitter in photoreceptors. Variations in glutamate production are responsible for the perception of darkness and light.
• In the dark, photoreceptors continuously produce glutamate. On bipolar cells (those that sense light) are inactivated and off bipolar cells (those that sense darkness) are activated. Off bipolar cells that indicate the absence of light form impulses that reach the brain through the optic nerve, creating a sense of darkness.
• In the presence of light, photorecptors do not produce glutamate. On bipolar cells become active and off bipolar cells become inactive. On bipolar cells that indicate the presence of light form impulses that reach the brain through the optic nerve, creating a sense of vision.

Colour vision

• In the retina, there are three types of cone cells recognise primary colours.
• S – cones show better sensitivity at short wavelengths (blue light), M – cones at medium wavelengths (green light) and L – cones at longer wavelengths (red light).
• Colour vision is made possible when the three types of cones get stimulated in varying proportions when exposed to coloured light depending upon the intensity and wavelength of light.
• When red and green cones are stimulated together, the perception of yellow colour is formed.
• The stimulation of all the three types of cones creates the sensation of white light.
• The gene responsible for the production of pigments in cone cells which are sensitive to green and red are found in the X chromosome.
• The gene which is responsible for the production of blue cone pigment is found in chromosome 7.
• Impulses related to the image formed in both eyes reach the visual centre of the brain through the optic nerve.
• Since each eye receives light from different angles, there will be two slightly different images on the retina. These two images are sent to the visual cortex in the brain. The brain compares these images and combines them(fusion). This process is known as binocular fusion.
• Binocular fusion will help to determine the difference between the two images. Thus, we get 3D vision. It enables to understand how distant or near objects are, and also to perceive depth.
• World Sight Day is observed on the second Thursday of October.
• The World Health Organisation (WHO) and the International Agency for the Prevention of Blindness (IAPB) call for the observance of this day to raise awareness on the eye healthcare.
• WHO eyes, a free application available in 14 languages enables free eye test for ages 8 and above.
• Donating eyes can give vision to two blind people.
• Cornea gets surgically transplanted. It is beneficial for those who have lost their vision due to the damage of the cornea.
• Each one of us has a responsibility to adopt a carelul life style to care for the eyes and to develop a positive attitude towards eye donation.
• There are several charts used to test visual acuity. Among them, the commonly used one is Snellen Chart.
• Snellen Chart consists of rows of letters or symbols that decrease in size from top to bottom
• Modern devices are used for eye test – Retinoscopes, Tonometers and Ishihara plates.

page 88 PROJECT
Topic
The teenager’s screen time
Hypothesis
If teenagers spend excessive time on screens, it may negatively affect their physical health, mental well-being, sleep quality, and personal and social relationships. On the other hand, moderate and mindful screen usage can support learning and healthy communication.

Planning
To study this topic, the following steps will be taken
Literature Review – Gather information from books, articles, and websites about screen time and its effects. Survey or Questionnaire – Prepare simple questions to ask classmates or peers about their daily screen time, sleep habits, and social activities

Daily Screen Usage

• How many hours do you spend on screens each day (including mobile, TV, computer, tablet)? Less than 1 hour/ 1 – 2 hours/ 2 – 4 hours /More than 4 hours
• What do you mostly use screens for? Studying/online classes Social media (WhatsApp, Instagram, etc.)/Watching videos/movies/ Playing games/Chatting or video calls

Sleep Habits

• Do you use your phone or other screens just before sleeping? Yes/ No
• On average, how many hours do you sleep at night? Less than 5 hours/5 – 6 hours/ 6 – 8 hours/ More than 8 hours
• Do you find it hard to fall asleep or stay asleep? Often/Sometimes/ Rarely/Never

Health and Well-being

• Do you experience any of the following due to long screen use? Eye strain/ Headache/Neck/back pain/ Laziness/ All of these/ None of these
• How often do you take breaks while using screens? Every 20-30 minutes/ Every hour/ Rarely/Never

Personal and Social Life

• Has screen time affected the time you spend with family or friends? Yes, I spend less time with them now/ No, my screen time is balanced
• Do you prefer chatting online rather than talking face-to-face? Yes/Sometimes/No

Your Opinion

• Do you think you spend too much time on screens? Yes/No/ Not sure
• Would you like to reduce your screen time? Yes/No/ Maybe

Data Collection
Collect responses and record observations based on screen time habits and lifestyle patterns.
Analysis
Compare the responses to see how screen time is linked to changes in health, sleep, and relationships.
Conclusion and Suggestions
Draw conclusions from the findings and suggest ways to maintain a healthy balance in screen use.

EAR
Hearing

• Hearing is the combined experience of the ears and the brain.
• The human ear also plays a major role in maintaining the balance of the body.

• Outer ear – Pinna, Auditory canal, Tympanum
• Middle ear – Ear oscicles, Eustachian canal
• Inner ear – Vestibule, Cochlea, Vestibular nerve, Auditory nerve
• Pinna – Directs the sound waves into the auditory canal, Helps to identify the direction from which sound is produced., Protects the auditory canal to some extent from foreign particles.
• Auditory canal – It directs sound waves to the tympanum and protects the tympanum from foreign particles.
• The hair inside the auditory canal, earwax and sebum secreted by glands in its wall help to prevent dust and germs from entering the ear.
• Like tears, ear wax also has disinfectant properties.
• Tympanum or eardrum is 9 – 10 mm in diameter and has only 0.1 mm thickness.
• In the middle ear, the ear ossicles are arranged in connection with tympanum.
• The tympanum vibrates in accordance with the sound waves. These vibrations make the bones in the ear ossicles vibrate as well.
• The eustachian canal is a long tube that is 4 cm long that connects the middle ear to the pharynx.
• Normally eustachian canal is closed, but it opens during chewing, blowing the nose etc.
• Eustachian canal helps to balance the pressure on both sides (middle ear and the atmospheric air in the outer ear) of the tympanum. It also facilitates the flow of mucus and fluids from middle ear to the pharynx.

The sense of hearing

• Sound waves vibrate the tympanum. From there the vibration passes through the ear ossicles and then vibrates the oval window.
• The structure of the oval window is also similar to that of the tympanum.
• The cochlea, having the shape of a snail shell, has three chambers, oval window is the membrane that covers the opening towards the upper chamber.
• The upper and lower chambers of cochlea are filled with a fluid called perilymph. The middle chamber is filled with endolymph.
• The Organ of Corti where the auditory receptors are present is situated in the basilar membrane between middle and lower chambers of cochlea.
• The vibrations that reach the hair cells present here generate impulses. These impulses reach the brain through auditory nerve resulting in the sense of hearing.

Maintaining Body Balance

• The part of the inner ear that maintains body balance is the vestibular system, which includes three semicircular canals, vestibule and hair cells.
• The endolymph present in the canals, which are arranged perpendicular to each other, moves with the rotational movement of the head. As a result of this movement, the hair cells present here get stimulated and impulses are formed.
• The utricle and saccule of the chamber called the vestibule also contain hair cells. The linear movement of the head generates impulses in these hair cells.
• When the impulses reach the brain through the vestibular nerve, the brain maintains body balance by receiving impulses from the eyes and muscles as well.

Hearing impairments

• Hearing impairments occur due to many reasons.
• Sound that travels in the form of waves can be transmitted only through a medium.
• A sound that can be heard in a condition of complete silence is represented as zero decibel.
• For every 10 decibels, the intensity of the sound increases tenfold.
• In a normal conversation, intensity of the sound will be between 40 and 50 decibels. It can be up to 60 decibels, while speaking loudly.
• The normal sound of the honking of a car horn is 70 decibels, while that of an air horn is 100-110 decibels.
• Intensity of noise above 80 decibels is extremely annoying.
• Noise pollution is a danger that is most harmful and unfortunately, the most neglected of all the environment pollutions that we face today.
• Hearing of loud noise (above 85 decibel) for a short time and less noise with a lesser intensity (below 55 decibel) for a very very long time can cause permanent hearing impairment.

Olfaction

• The tongue and nose are two interconnected sense organs.
• While breathing, the particles responsible for smell enter the nasal cavity. Then it gets dissolved in the mucus produced by mucus membrane.
• Millions of olfactory neurons in the mucus membrane get stimulated by special olfactory particles.
• Receptors generate impulses, and they travel through the olfactory nerve to reach the part of the brain recognising smell, and the sense of smell is effected.

Taste

• One can identify the smell of the food even before tasting it.
• Taste buds play a crucial role in enjoing the food by helping us to perceive the natural flavours of food.
• Food made with natural ingredients is safe and healthy rather than the taste of artificial additives or harmful substances.
• A taste bud will have about 100 chemoreceptors.
• Microvilli from each chemoreceptor, reach the minute pores present in the papilla.
• Saliva enters through this pore. Substances that give rise to taste are dissolved in saliva and stimulate chemoreceptors.
• The impulses produced by these molecules in the chemoreceptors reach the brain through the nerve and make the sense of taste.
• The main tastes we recognise are sweet, sour, salty, pungent, bitter and umami.

Skin
There are various receptors present in skin for carryout different functions. They are,

Part	Name	Functions
1	Independent nerve endings	Pain, temperature fluctuations
2	Merkel disc	Touch, pressure and movement of hair
3	Meissner corpuscles	Shape, quantity and structure of objects
4	Krause end bulbs	Cold, touch
5	Rufini end organ	Intense touch, pressure, heat
6	Root hair plexus	Helps to find out the movement of hair
7	Pacinian corpuscles	Vibration, touch with a high frequency

SENSORY DIVERSITY IN ORGANISMS
Sensory diversity in organisms

• Amoeba/Bacteria – Detects the presence of chemicals in the surroundings and move against them.
• Euglena – The eyespot (stigma) helps to detect light and move towards it.
• Insects – The compound eye made up of Ommatidia. The Antenna helps to detect smell and touch.
• Bat – Ears and special type of echo location organ helps in hunting and travelling.
• Hawk – Eyes with high vision, systems for long distance vision and detecting ultra violet radiation.
• Snake – Jacobson’s organ helps to detect smell.
• Dog – Highly sensitive olfactory receptors (300 million) are found.
• Human senses are the powerful tools that connect us to the world around us.