RBSE Solutions For Class 12 Biology Chapter 27: Sensory Organs of Human; Sense Organs | Textbook Important Questions & Answers

RBSE Class 12 Biology Chapter 27- Sensory Organs of Humans provides complete information related to the sense organs of humans. The organ of sight – eye, the organ of hearing – ear, the organ of taste – tongue, the organ of smell-nose and the organ of touch-skin. This chapter also provides in-depth explanations related to structure and functions related to the five sense organs, their mechanisms, disorder and a lot more.

These important questions help students to enhance their conceptual knowledge and are completely prepared from the exam point of view, helping students revise the entire chapter.

The Rajasthan Board Class 12 Solutions help students by providing a strategy to prepare for various board examinations and also for medical exams like NEET, AIIMS, etc. By practising these important questions, students can gain deep knowledge about the topic.

RBSE Class 12 Biology Chapter 27 Important Questions

RBSE Biology Chapter 27: MCQ Type Questions

Q.1. The shape of the malleus and the ear ossicle is ________.

(a) Oval shaped

(b) Hammer shaped

(c) Horseshoe-shaped

(d) None of the above

Sol: (b) Hammer shaped.

Q.2. Which of the following is the function of cones in the eye?

(a) Secretion and balances

(b) Vision in darkness

(c) Monocular vision

(d) Vision in the high beam light and colour differentiation

Sol: (d) Vision in the high beam light and colour differentiation.

Q.3. Which of the following is the condition related to Myopia?

(a) Monocular vision

(b) Unable to see the nearer object clearly

(c) Unable to see the distant object clearly

(d) None of the above

Sol: (c) Unable to see the distant object clearly.

Q.4. Which of the following parts of the internal ear is responsible for body balance?

(a) Incus

(b) Sacculus

(c) The organ of Corti

(d) Sacculus, Utriculus and semicircular canals

Sol: (d) Sacculus, Utriculus and semicircular canals.

Q.5. How many numbers of bones are present in the middle ear?

(a) Two

(b) Three

(c) Six

(d) Nine

Sol: (b) Three.

Q.6. Which of the following is the middle layer of the eye?

(a) Sclera

(b) Lens

(c) Choroid

(d) Retina

Sol: (c) Choroid.

Q.7. Which of the following is an olfactory organ?

(a) Eye

(b) Ear

(c) Nose

(d) Skin

Sol: (c) Nose.

Q.8. Which of the following is a symptom of Labyrinthitis?

(a) Pain in the ear

(b) Permanent deafness

(c) Chronic inflammation

(d) All of the above

Sol: (b) Permanent deafness.

Q.9. The deficiency of ________ causes night blindness.

(a) Vitamin-D

(b) Vitamin-A

(c) Vitamin-B

(d) Vitamin-C

Sol: (b) Vitamin-A.

Q.10. How many layers are present in the human eye?

(a) Three

(b) Four

(c) Two

(d) Nine

Sol: (a) Three.

RBSE Biology Chapter 27: Short Answer Type Questions

Q.1. Write the names of bones present in the middle ear.

Sol: The middle ear is composed of three bones:

1. Malleus.
2. Incus.
3. Stapes.

Q.2. Where is the tectorial membrane found?

Sol: The tectorial membrane is the part of the ear, which is found within the scala media of the cochlea.

Q.3. What are the functions of rods and cones?

Sol: Rods and cones are the part of the eye- the vision. Rods are responsible for the general vision. They are also active in the dim light. Cones are mainly responsible for the colour vision and are active in both moderate and bright light.

Q.4. Which structure of the ear completes the mechanisms of the body balance?

Sol: The cochlea, consisting of the three semicircular canals, saccule and utricle, which are responsible for maintaining balance.

Q.5. What is the role of the eustachian tube in the ear?

Sol: The eustachian tube present in the middle ear is mainly responsible for equalizing and maintaining the ear pressure and draining fluid from the middle ear.

Q.6. What is the yellow spot?

Sol: Yellow spot is the smallest area on the retina, present at the posterior pole of the eye and lateral to the blind spot. The yellow spot is the area on the retina where maximum light falls. These regions are very sensitive to the bright light, which is mainly because of the presence of cones in this region.

Q.7. What is the internal ear?

Sol: The internal ear is also called the membranous labyrinth. It is a semi-transparent structure, which is situated in the bony labyrinth. The internal ear is surrounded by the perilymph. It consists of two types: Vestibule and Cochlea.

Q.8. List out the names of muscles found in the human eyes.

Sol: The human eyes consists of six muscles:

1. External rectus muscle.
2. Internal rectus muscle.
3. Superior rectus muscle.
4. Inferior rectus muscle.
5. Superior oblique muscle.
6. Inferior oblique muscle.

Q.9. What are the Sensory Organs?

Sol: Sensory organs are specialized organs which function by receiving feelings from the brain. Humans have five different types of sensory organs and sense organs.

1. The organ of sight – Eye.
2. The organ of hearing- Ear.
3. The organ of touch- Skin.
4. The organ of taste- Tongue.
5. The organ of smell- Nose.

Q.10. What is myopia?

Sol: Myopia, also called nearsightedness or shortsightedness. This is a common vision disorder that occurs when the eye loses the ability to see the distant object clearly. This is caused either due to the increased focal power of the lens or when the eyeball becomes larger.

Q.11. How many glands are present in the human eye.

Sol: There are three types of glands found in the eye.

1. Meibomian glands.
2. Moll’s glands
3. Lacrimal glands or tear glands

Q.12. What is colour blindness?

Sol: Colour blindness is the syndrome caused by the failure of light-sensitive cells – rod cells and the cone cells. In these conditions, a person cannot see, identify and differentiate any colours like blue, green and red.

Q.13. What are tear glands?

Sol: The glands present on the corner of the upper eyelid are called the tear glands. This functions by producing tears and by keeping the eyes wet and clean.

Q.14.What is the blind spot?

Sol: Blindspot is the small portion of the visual field that corresponds to the lack of light. This is the region of an eye, where there is no formation of images. They are insensitive to light because of the absence of both cones and rods in this region of the eye.

Q.15. What is a cataract?

Sol: It is an eye disease related to age factors. i.e., it is mainly seen in aged people. Cataract disease is also known as salad motia. In this condition, the eye lens slowly becomes opaque, which affects the entry of the light into the eye.

Q.16. What is the function of the ear?

Sol: The ear has two main sensory functions:

1. Hearing
2. Balancing the body.

Q.17. Why do we feel a sense of smell?

Sol: The nose is the main sense organs, which is involved in the sense of smell. Nose functions by observing the chemical senses of chemical molecules, which are received with air and tongue observed by direct contact.

Q.18. What is the Menier disease?

Sol: The Menier disease is a disorder of the inner ear, in which the sensory cells of ampulla and cochlea are destroyed. This condition may result in permanent deafness.

Q.19. Define Astigmatism?

Sol: It is the eye disorder caused due to the abnormal shape of the cornea, in which different curvatures in different regions of cornea appear. This disorder can be corrected by the use of cylindrical lenses.

Q.20. What is the function of the internal ear?

Sol: The semicircular canals, utricle, sacculus and the cochlea are the parts of the internal ear. The internal ear has two main functions:

1. Cochlea functions by providing a sense of hearing.
2. semicircular canals, utricle and saccule are involved in the realization of the disorder in the body balance.

RBSE Biology Class 12: Long Answer Type Questions

Q.1. What are the Symptoms of Colorblindness

Sol: The symptoms of this eye syndrome include:

1. Rapid eye movement.
2. Sensitivity towards the bright light.
3. Trouble in seeing colours and the brightness of colours.
4. The problem in identifying the differences between colours shades.

Q.2. Explain the Structure of an Eye with the help of a neat labelled diagram.

Sol: The Structure of an Eye

The structure of the eye is mainly divided into two parts based on their location.

The External Structure of an Eye:

The external structure of the eye comprises the following parts. These parts are visible from the outside.

These include the following:-

1. Sclera: The white, tough, thick layer sheath and the outermost layer of the eye. It functions as a protective layer, which provides protection for the internal parts of the eye and maintains the shape of the eyeball.
2. Conjunctiva: It is a thin transparent membrane or a tissue that lines the inside of the eyelids and covers the sclera – the white part of the eye. It keeps the eyes moist and clear with the help of the mucus and tears from the tear glands.
3. Cornea: The transparent and front part of the eye that covers the pupil, iris, and anterior chamber. It is spread over the pupil and the iris. The main function of the cornea is the refraction of the light entering the eyes.
4. Pupil: It is the small opening or a black hole, which is located in the centre of the iris of the eye. It functions by allowing the entry of the light.
5. Iris: The thin, annular structure of the eye, which is located between the cornea and the lens. The function of the iris is to limit the amount of light that passes through the lens to the retina.

The Internal Structure of an Eye:

1. Lens: It is a transparent, biconvex in shape, and an adjustable part of an eye, which is situated just behind the iris. It is a semisolid made up of a soft gelatin tissue. The lens remains in its position with the help of a suspensory ligament, which joins the lens with the ciliary body.
2. Retina: It is the innermost sensory layer of the eye present at the back of the eye where all the images are formed. It is very sensitive towards the light because of the presence of Photoreceptors. Retina has two types of sensory cells – Rods and the cones. The rods contain photosensitive pigments, which are formed by vitamin-A. There are more numbers of rods compared to the cones. A human eye is composed of 115 millions of rods and 16.5 millions of cones. Owing to this, humans are able to differentiate between the lights. Functions of the retina are The conversion of the light rays into the impulses and transformation of signals from eye to the brain through the optic nerve.
3. Optic nerve: It is located behind the retina and at the end of the eyes. This is a transparent, semi-solid, a jelly-like substance, which performs a vital role in protecting the eyes. that covers the interior portion of the eyes.
4. It is mainly responsible for the formation of the image by carrying the nerve impulses from the photoreceptors to the human brain.
5. Aqueous Humour: It is the transparent, watery fluid-like substances with low protein concentrations. It is mainly found in between the area of the lens and the cornea. It is mainly involved in the nourishment of both the lens and the cornea.
6. Vitreous Humour: It is a transparent, jelly-like substance present behind the lens. It covers the interior portion of the eyes and is mainly involved in the maintenance of the shape of the eye, nourishes the lens and also maintains pressure by the refraction of light before it reaches the retina.

Q.3.What is the iris? What is the function of the iris? How many layers does it have?

Sol: Iris is the external structure of an eye. It is a pigmented layer of tissues that make up the coloured portion of the eye.

Its primary function is to control the size of the pupil, depending on the amount of light entering it.

The iris consists of two main layers:

1. Pigmented epithelial cells.
2. Stroma, the front pigmented fibrovascular layer

Q.4. What is eye disease? List out the different types of common eye disease.

Sol: The eye disease is a disorder that destroys tissues and other parts of the eye. Eyes are the most sensitive sense organs and play an important role in our life. There are different types of eye diseases, which can either be small and curable. In some rare cases, eye diseases can also lead to a permanent loss of vision.

There are different factors behind the causes of eye diseases. These factors include age, stress, heredity, infections, nutritional deficiencies, injuries or accidents, etc

The following is a list of human eye disease:

Myopia.

Types of common eye disease.

1. Cataract.
2. Astigmatism.
3. Conjunctivitis.
4. Hypermetropia.
5. Vision Changes.
6. Colour blindness.
7. Retinal disorders.
8. Dry and Itchy Eyes.
9. Optic nerve disorders.

Q.5. Explain the working process of an Eye.

Sol: The methodology of an eye can be explained as follows:

The entrance of light.

After the reflection from an object, the light rays enter the eye through the transparent structures- Cornea, Conjunctiva, Lens, Aqueous humour and Vitreous humour.

Formation of an Image.

Due to the convexity of the cornea, the light rays bend to some extent and later on the lens converges by which an image is formed on the retina.

Nature of the image.

The formed image is inverted and is a real image.

Formation and transmission of the nerve impulse.

The light energy produces chemical changes in sensory cells – Rods and Cones. The nerve impulses are formed by these changes, which are sent to the brain through the optic nerve.

Recognition and Realization.

Our brain understands the image in many ways and guesses its meaning, i.e. it sees the object is erect, while the image formed on the retina is inverted.

Focusing.

The process of focusing the images on the retina is known as accommodation or focusing. To focus means to change the convexity of the elastic lens.

Q.6. Explain the structure and functions of the human ear.

Sol: The ear is a sensitive organ of the human body. It has two main sensory functions: hearing and maintaining a sense of balance.

Structure of the Human Ear.

The human ear consists of three parts:

1) External ear.

The external ear mainly consists of two main parts:

Ear Pinna or Auricle.

It is composed of thin, fibroelastic cartilage, which is slightly curved, supported by the bone and covered by a layer of skin. It is an immovable part of the ear, mainly because of the presence of auricular muscles, which are vestigial in it. It has the cavity, known as Concha. Ear pinna collects the sound waves and sends them into the external auditory meatus.

External Auditory Meatus

The concha opens into a narrow canal, which is called the external auditory meatus. This extends up to the tympanic membrane. In external auditory meatus, sweat glands are modified into cerumen glands, which secrete cerumen or earwax.

2) Middle ear.

The middle ear comprises the following parts:

Tympanic Cavity

It is a narrow air-filled cavity separated from the external ear by tympanic membrane and from the inner ear by the bony wall. The tympanic cavity has an auditory tube known as the eustachian tube in its anterior wall.

Eustachian Tube

The eustachian tube is a 4cm long tube that equalizes air pressure on either side of the tympanic membrane. It connects the tympanic cavity with the nasopharynx.

Ear Ossicles

These are responsible for transmitting sound waves from the eardrum to the middle ear. There are three ear ossicles in the human ear:

Malleus: It is a hammer-shaped part that is attached to the tympanic membrane through the handle and incus through the head. It is the largest ear ossicle.

Incus: An anvil-shaped ear ossicle connected with the stapes.

Stapes: It is the smallest ossicle and also the smallest bone in the human body.

3) Internal ear.

It is suited in the cavity of the temporal bone that is called the bony labyrinth. Basically internal ear consists of two main parts:

Cochlea.

It is the long, coiled structure, which resembles the structure of a coil of the snail’s shells. It has two and a half turns. Its terminal cycling cavity is divided into three parallel ducts, which are separated by the membranes. Liquid endolymph is filled in these ducts. Areas with the sensory cells related to hearing are present within the middle duct, known as Corti hair organ or the organ of Corti.

Vestibule.

It is related to maintaining body balance. It has three semicircular canals, which are situated at the right angle of each other. One of the parts is attached to the cochlea, one with the utriculus, and other is differentiated into the sacculus.

Structure of a human Cochlea

Q.7. Explain the working process of an Ear.

Sol: It is also called the mechanism of hearing.

Ear pinna collects the sound waves, which then enter into the external auditory meatus, which produces vibrations in the tympanic membrane.

After this, the vibrations reach the internal ear through the three ear ossicles- malleus, incus stapes and fenestra ovalis.

These vibrations provide movement to the liquid present in the cochlea. Organs of the Corti receive the vibrational movements from the fluid and send it into the cochlear nerves, as the nerve impulses. These nerves send the impulses to the brain.

Q.8. Explain about the sense of taste and smell.

Sol: The tongue, the sense of taste provides the feeling of the taste and the nose, provides the sense of smell. Both tongue and the nose sense the smell and it depends on the nature of the chemical compounds coming in its contact.

Tongue- The sense of taste

The tongue is a muscular organ in the mouth covered with a moist, pink tissue called the mucosa. It is involved in licking, tasting, breathing, swallowing, and speaking. The papillae present on the tongue is covered by a number of taste buds. There are several nerves in the tongue that help in transmitting taste signals to the brain, and thus help in taste sensation.

The sense of taste is known by the tongue and it happens when the substances come in direct contract with the taste buds, which are found on the tongue.

Nose – The sense of smell

The nose is the primary organ of smell and functions as an important respiratory organ in the body. Besides this, it is also involved in functions such as hearing and tasting.

The sense of smell is known by the nose and it happens, when the chemicals come in contact with the sensory epithelium cells of the nose. i.e. when the chemical molecules come in contact with the sensory epithelium cells through the breathing air, then the sensory epithelium cells of the nose are excited and the sense of the smell is experienced.

Q.9. Describe the type of sense organs.

Sol: Types of sense organs.

There are different types of sense organs in the body, which functions by receiving the stimuli.

Sir Charles Scott Sherrington, an English neurophysiologist, distinguished three main groups of sense organs:

• Exteroceptors.

This includes Tangoroceptors, Photoreceptors, Baroreceptors, Algisoroceptors, Skin Receptors, etc.

• Interoceptors.

This includes sense organs found in the visceral organs.

• Proprioceptors.

This includes sense organs found in the involuntary muscles, joints, tendons, ligaments, etc.

Later, George Howard Parker, an American zoologist classified sense organs into three main groups based on the nature of the stimuli.

• Chemoreceptors.

This includes Gusto Receptors and olfactory receptors.

• Mechanoreceptors.

This includes Algis Receptors, Tangoreceptors, Pressuroreceptors, etc.

• Radio Receptors.

This includes Thermoreceptors, Photoreceptors, etc.

Both exteroceptors and interoceptors remain interconnected by somatic and visceral sensory nerve fibres. The receptor sends the stimuli to the central nervous system (CNS).

The below table provides the complete details of the sense organs found in human beings.

Q.10. List out the disorder of the human ear.

Sol: The ear disease is a disorder that destroys the internal part of the ear. Ears are the most sensitive sense organs and play an important role in our life by providing the sense of hearing. There are different types of ear diseases, which can either be small and curable and some can also lead to a permanent loss of hearing or deafness.

Listed below are the different types of ear disease:

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