RBSE Solutions Class 12 Biology Chapter 27 Man-Sensory Organs (Sense Organs)

Rbse Class 12 Biology Chapter 27 Multiple Choice Questions

 

Question 1. The shape of ear ossicle, malleus is:
(a) Hammer like
(b) Stirrup like
(c) Oval
(d) None of the options
Answer: (a) Hammer like
In simple words: The malleus, one of the tiny bones in your ear, has a shape like a hammer. These small bones help in hearing by passing sound vibrations. It is one of three small bones that help you hear.

🎯 Exam Tip: Remember the shapes of the three ear ossicles: Malleus (hammer), Incus (anvil), and Stapes (stirrup) for easy identification.

 

Question 3. Man in the eye defect Myopia:
(a) Unable to easily see nearer objects
(b) Unable to easily see distant objects
(c) Unable to be the monocular vision
(d) None of the options
Answer: (b) Unable to easily see distant objects
In simple words: When a person has myopia, also known as nearsightedness, they find it difficult to clearly see things that are far away. Objects that are close appear clear, but distant ones look blurry. Myopia means you can't see far-off things clearly.

🎯 Exam Tip: Myopia is a common refractive error where light focuses in front of the retina, making distant objects appear blurry, hence the difficulty in seeing far away.

 

Question 4. The balance est lavish by the part of the internal ear is
(a) Incus
(b) Sacculus
(c) Sacculus, Utriculus, semicircular canals
(d) Organs of Corti
Answer: (c) Sacculus, Utriculus, semicircular canals
In simple words: The internal ear is responsible for maintaining the body's balance. Specifically, the sacculus, utriculus, and semicircular canals within the inner ear work together to detect head movements and position, sending signals to the brain to help you stay balanced. They help your body stay balanced by sensing how your head moves.

🎯 Exam Tip: Remember that the vestibular system, comprising the sacculus, utriculus, and semicircular canals, is key for balance and spatial orientation in the body.

Rbse Class 12 Biology Chapter 27 Very Short Answer Type Questions

 

Question 1. Write the names of bones present in the middle ear.
Answer: The middle ear contains three tiny bones that help transmit sound. These bones are called the Malleus, Incus, and Stapes. They work together like a small lever system to amplify sound vibrations.
In simple words: The three bones in your middle ear are the Malleus, Incus, and Stapes. They help carry sound deeper into your ear.

🎯 Exam Tip: Always list all three ossicles correctly: Malleus, Incus, and Stapes, ensuring accurate spelling for full marks in an exam.

 

Question 2. Where the tectorial membrane is found?
Answer: The tectorial membrane is a special gel-like structure found within the cochlea of the ear. It is located in the Scala Media, which is one of the fluid-filled compartments of the cochlea. This membrane plays a vital role in converting sound vibrations into nerve signals. You can find the tectorial membrane inside the ear's cochlea.
In simple words: You can find the tectorial membrane inside the ear's cochlea, specifically in the Scala Media. It helps turn sounds into messages for the brain.

🎯 Exam Tip: Specify 'Scala Media' and 'cochlea' when describing the location of the tectorial membrane, as these are precise anatomical terms expected in answers.

 

Question 4. Which structure of the ear completes the mechanism of body balance?
Answer: The structures in the inner ear that complete the body's balance mechanism are the Cristae and Maculae. Cristae are found in the semicircular canals and detect rotational movements, while Maculae are in the utricle and saccule, detecting linear acceleration and head position. These structures work together to tell your brain about your head's movement and position.
In simple words: The Cristae and Maculae in your inner ear work together to help you keep your balance. They tell your brain about your head's movement and position.

🎯 Exam Tip: Distinguish between Cristae (for rotational balance in semicircular canals) and Maculae (for static and linear balance in the utricle and saccule) to show a thorough understanding.

Rbse Class 12 Biology Chapter 27 Short Answer Type Questions

 

Question 1. What is the role of the eustachian tube in the ear?
Answer: The eustachian tube plays an important role in the ear by ensuring that the air pressure inside the middle ear stays the same as the air pressure outside. This balance is crucial for the eardrum to vibrate correctly and for clear hearing. It opens when you swallow or yawn, equalizing the pressure, which is why your ears pop. This helps your eardrum work well and makes sure you can hear clearly.
In simple words: The eustachian tube keeps the air pressure inside your middle ear equal to the outside air. This helps your eardrum work well and makes sure you can hear clearly.

🎯 Exam Tip: Highlight the primary function of the Eustachian tube as 'equalizing air pressure' in the middle ear for proper eardrum function, a key term for examiners.

 

Question 2. Name the places found in the retina in the sequence where vision is the best and where nothing is seen.
Answer: On the retina, the part of the eye that senses light, there are two key areas:
1. Site of Best Vision - Yellow Spot (Macula Lutea): This area, also known as the macula lutea, provides the sharpest and most detailed vision because it has a high concentration of cone cells. This high density of cones allows for fine visual discrimination.
2. Site of No Vision - Blind Spot (Optic Disc): This area is called the blind spot because it lacks any photoreceptor cells (rods and cones), so it cannot detect light. It's where the optic nerve leaves the eye, creating a natural gap in vision. The retina has two special spots.
In simple words: The 'Yellow Spot' is where you see things clearest. The 'Blind Spot' has no light sensors, so you can't see anything there.

🎯 Exam Tip: Clearly differentiate the 'Yellow Spot' (macula lutea) for sharp vision and the 'Blind Spot' (optic disc) where the optic nerve exits and no vision occurs, mentioning the reason for each.

 

Question 3. Write the names of muscles found in the human eyes.
Answer: The human eye is moved and controlled by six muscles, known as extraocular muscles. These muscles allow the eye to move in many directions, ensuring we can track objects and focus correctly. They are:
1. External rectus muscle
2. Internal rectus muscle
3. Superior rectus muscle
4. Inferior rectus muscle
5. Superior oblique muscle
6. Inferior oblique muscle
These muscles work together to provide a wide range of eye movements.
In simple words: Six muscles help move your eyes. They are the External rectus, Internal rectus, Superior rectus, Inferior rectus, Superior oblique, and Inferior oblique muscles.

🎯 Exam Tip: List all six extrinsic eye muscles accurately for a complete answer, as they are crucial for eye movement and coordination to score full marks.

 

Question 4. What is myopia?
Answer: Myopia, commonly known as nearsightedness or short-sightedness, is an eye condition where distant objects appear blurry while close objects are seen clearly. This happens because the eye's lens has too much focusing power, making it more convex, or because the eyeball itself has grown too long. To correct this vision problem, people with myopia typically use biconcave lenses, often referred to as 'minus lenses'. This type of lens helps to diverge light rays before they enter the eye, allowing them to focus correctly on the retina.
In simple words: Myopia is when you can't see far things clearly; it's also called nearsightedness. It happens because your eye lens is too strong or your eyeball is too long. Glasses with 'minus lenses' can fix it.

🎯 Exam Tip: Define myopia clearly by mentioning the blurriness of distant objects, its causes (lens power or eyeball length), and the corrective measure (biconcave lenses) for a thorough explanation.

 

Question 5. What do you mean by colour blindness?
Answer: Colour blindness is a condition where a person cannot see certain colors or distinguish between them correctly. It is a hereditary eye disorder, first described by Horner, and mainly comes in two types: red-green colour blindness and blue colour blindness. Red-green colour blindness is the most common, occurring due to the absence of specific red-green cone cells in the retina. People with this condition struggle to identify red, green, yellow, and orange. This condition is a sex-linked disease, meaning it is passed through genes on the X-chromosome. Females can carry the gene without showing symptoms, while males are more commonly affected. For instance, if a carrier mother and a normal father have children, there is a chance of normal, carrier, and colour-blind offspring in certain percentages. Similarly, the inheritance pattern changes if the father is colour-blind.
In simple words: Colour blindness means you can't see some colors well. It's passed down in families, often affecting males. The most common type is red-green, where special cells in the eye are missing.

🎯 Exam Tip: When explaining colour blindness, mention its hereditary nature, the role of cone cells, the common types (red-green), and its sex-linked inheritance pattern to cover all key aspects.

Rbse Class 12 Biology Chapter 27 Essay Type Questions

 

Question 1. Describe various eye diseases in detail.
Answer: Our eyes can be affected by several conditions that impact our vision. Here are some common eye diseases:
1. Myopia (Nearsightedness): Myopia, or nearsightedness, makes distant objects appear blurry. This can happen if the eye's lens focuses light too strongly (becomes more convex) or if the eyeball is too long. Biconcave lenses, also known as 'minus lenses,' are used to correct this condition.
2. Hypermetropia (Farsightedness): Hypermetropia, or farsightedness, causes difficulty in seeing nearby objects clearly. It occurs when the lens has a reduced focusing power (less convex) or the eyeball is too short. It can be corrected using biconvex lenses, often called 'plus lenses,' which help to converge light rays correctly.
3. Cataract: Cataract is an age-related eye disease where the eye's natural lens slowly becomes cloudy or opaque. This cloudiness prevents light from properly reaching the retina, leading to blurry vision. It is also known as 'salad motia'. Treatment usually involves surgically removing the cloudy lens and replacing it with an artificial one, or using spectacles with convex lenses.
4. Astigmatism: Astigmatism is an eye condition caused by an irregularly shaped cornea, where different parts of the cornea have different curvatures. This uneven shape causes light to focus improperly on the retina, resulting in blurred or distorted vision at all distances. Cylindrical lenses are used to correct astigmatism, as they have different refractive powers in different meridians.
5. Conjunctivitis: Conjunctivitis, also known as 'pink eye,' is an inflammation or irritation of the conjunctiva, the clear membrane covering the white part of the eye and the inside of the eyelids. It is typically caused by viral or bacterial infections. Symptoms include redness, itching, and discharge from the eye. It can be quite contagious.
6. Colourblindness: Colour blindness is a hereditary condition where a person cannot distinguish between certain colors, most commonly red and green. It is often a sex-linked genetic disorder, affecting the cone cells in the retina. The inability to differentiate colors like red, green, yellow, and orange is characteristic of this condition. There is currently no cure, but certain colored lenses can help.
In simple words: Many eye problems can affect our vision. Myopia makes distant things blurry, and hypermetropia makes near things blurry. Cataract makes the eye lens cloudy, while astigmatism means the eye's front part is shaped wrongly. Conjunctivitis is an eye infection, and colour blindness means you can't see some colors well.

🎯 Exam Tip: For an essay question on eye diseases, ensure you describe the cause, key symptoms, and correction method for each disease mentioned to provide a comprehensive answer.

 

Question 2. Describe in detail the mechanism of hearing.
Answer: Hearing is a complex process that converts sound waves into signals the brain can understand. Here's how it works:
1. First, the outer ear, or pinna, collects sound waves and channels them into the external auditory canal.
2. These sound waves then reach the eardrum (tympanum), causing it to vibrate.
3. Any pressure differences in the middle ear caused by the vibrating eardrum are equalized by the eustachian tube.
4. Next, three tiny bones in the middle ear-the malleus, incus, and stapes (ossicles)-receive these vibrations and amplify them about 20 times. They pass these amplified vibrations to the oval window (fenestra ovalis).
5. The vibrations from the oval window are then balanced by the round window (fenestra rotunda), preventing pressure buildup inside the cochlea.
6. These vibrations make the fluid (perilymph) inside the inner ear move, which in turn causes the Reissner's membrane to vibrate.
7. The vibrating Reissner's membrane causes the fluid (endolymph) in the scala media to move. This movement causes the tectorial membrane to brush against the hair cells of the Organ of Corti.
8. Finally, the Organ of Corti, a special structure in the cochlea, converts these mechanical movements into electrical signals. These electrical signals are then sent to the brain through the auditory nerve (VIII cranial nerve), where they are interpreted as sound. This intricate pathway ensures that even faint sounds can be detected and processed.
In simple words: Sound waves enter your ear and make your eardrum shake. Small bones then make these shakes stronger. These strong shakes move fluid in your inner ear, which then tickles tiny hairs in the Organ of Corti. The Organ of Corti turns these tickles into messages for your brain, so you can hear.

🎯 Exam Tip: Detail each step from sound wave collection by the pinna to signal transmission by the auditory nerve, emphasizing the role of the eardrum, ossicles, and Organ of Corti for a complete answer.

 

Tongue & Nose:

 

Question 3. Describe the type of sense organs and describe them.
Answer: Sense organs are special body parts that detect different types of stimuli from our environment or from inside our body. These organs then send signals to the brain. Sherington classified sense organs into three main groups:
1. Exteroceptors: These organs detect stimuli from outside the body. Examples include tangoreceptors (for touch), photoreceptors (for light), rheoreceptors (for water currents), algisoreceptors (for pain), and skin receptors.
2. Interoceptors: These organs detect stimuli from inside the body, such as hunger, thirst, or pain from internal organs. They are found in the visceral organs.
3. Proprioceptors: These receptors give us a sense of our body's position and movement. They are found in muscles, tendons, joints, and ligaments, helping us maintain balance and posture. These ensure precise body coordination.
Parker further classified sense organs based on the type of stimulus they detect:
1. Chemoreceptors: These detect chemical stimuli, like taste (gustoreceptors) and smell (olfactoreceptors).
2. Mechanoreceptors: These respond to mechanical stimuli such as pressure, touch, and sound. Examples include algisoreceptors, tangoreceptors, and pressuroreceptors.
3. Radioreceptors: These detect changes in temperature and light. Examples include thermoreceptors and photoreceptors.
These various receptors are connected to the central nervous system through somatic and visceral sensory nerve fibers, which ensure that stimuli are properly conveyed and processed.
Here is a summary of some receptors and their associated senses:

In simple words: Our body has many sense organs to feel the world. Some sense things outside (like touch, sight), some feel inside (like hunger), and some tell us where our body parts are. Other ways to group them are by what they sense: chemicals (taste, smell), movement (touch), or light and heat. All these senses send messages to our brain.

🎯 Exam Tip: When describing sense organs, ensure you cover both Sherington's (Exteroceptors, Interoceptors, Proprioceptors) and Parker's (Chemoreceptors, Mechanoreceptors, Radioreceptors) classifications with clear examples for each to demonstrate comprehensive knowledge.

 

Question 4. Explain the structure of the inner ear.
Answer: The inner ear is a complex and delicate structure located within the temporal bone of the skull. It is also known as the membranous labyrinth, which is housed inside a protective bony labyrinth. The space around the membranous labyrinth is filled with a fluid called perilymph. The inner ear has two main parts:
1. Vestibule: This part includes the utriculus and sacculus, which contain maculae that are important for sensing static balance and linear acceleration. From the utriculus, three semicircular canals (anterior, posterior, and external) arise at right angles to each other. These canals detect rotational movements. The anterior and posterior canals share a common origin called the crus commune. Each semicircular canal has a swollen end called an ampulla. Both the semicircular canals and their ampullae are filled with a thick fluid called endolymph. The sacculus also has a macula, which is sensory to static balance, and it gives off an endolymphatic duct.
2. Cochlea: This is a spiral-shaped tube that originates from the sacculus. It has about 2.5 coils in rabbits and 2.75 coils in humans. Inside, the cochlea is divided into three fluid-filled chambers: the scala vestibuli, scala media, and scala tympani. The scala vestibuli and scala tympani contain perilymph and are connected by a small opening called the helicotrema. The scala media contains endolymph. A basilar membrane separates the scala media and scala tympani, while Reissner's membrane separates the scala vestibuli and scala media. The basilar membrane has a specialized structure called the Organ of Corti, which contains sensory hair cells (Deiter's, Hensen's, and pillar cells) with stereocilia and nerve fibers that form the VIII cranial nerve. Above the Organ of Corti is the tectorial membrane. The Organ of Corti is crucial for hearing, as it converts sound vibrations into nerve impulses. This intricate structure is essential for both hearing and maintaining balance.
In simple words: The inner ear is a tiny, complex part hidden deep inside your head, filled with fluid. It has two main parts: the vestibule, which helps with balance and sensing movement, and the cochlea, which is shaped like a snail and is for hearing. The cochlea has special cells in the Organ of Corti that turn sounds into messages for your brain.

🎯 Exam Tip: When describing the inner ear, include both its balance (vestibule, semicircular canals) and hearing (cochlea, Organ of Corti) functions, mentioning the key structures and fluids involved, and their specific roles.

 

Question 6. Describe the structure of the eye with diagrams.
Answer: The human eye is positioned within a bony socket called the eye orbit. Each eye is highly mobile due to the action of six voluntary and striated extrinsic eye muscles attached to it. These muscles control the precise movements of the eyeball. They are categorized as four rectus muscles and two oblique muscles:
1. **Anterior or External Rectus (Lateral Rectus):** This muscle is attached to the outer side of the eyeball and helps in moving the eye outwards. It is controlled by the Abducens cranial nerve.
2. **Posterior or Internal Rectus (Medial Rectus):** Attached to the inner side of the eyeball, this muscle moves the eye inwards. It is controlled by the Oculomotor cranial nerve.
3. **Superior Rectus:** Located on the upper-middle side of the eyeball, this muscle helps in rotating the eye upwards and slightly inwards. It is also innervated by the Oculomotor cranial nerve.
4. **Inferior Rectus:** This muscle is located on the lower-middle side of the eyeball and helps in rotating the eye downwards and slightly inwards. It is also innervated by the Oculomotor cranial nerve.
5. **Superior Oblique Muscle:** This muscle is connected between the external rectus and superior rectus. It is responsible for rotating the eyeball downwards and outwards, and is controlled by the Trochlear cranial nerve.
6. **Inferior Oblique Muscle:** Attached between the inferior rectus and external rectus, this muscle rotates the eyeball upwards and outwards. It is innervated by the Oculomotor cranial nerve.
In summary, the anterior and posterior rectus muscles mainly rotate the eyeball horizontally (inside and outside), while the superior and inferior rectus muscles primarily control vertical movements (up and down). The oblique muscles provide rotational stability and fine-tune eye movements. Together, these muscles ensure comprehensive eye mobility.
In simple words: Your eye sits in a bony hole and can move around because of six strong muscles. These muscles are named rectus and oblique muscles. They help your eye look up, down, left, and right. For example, the anterior rectus pulls the eye outward, and the superior rectus helps it look up.

🎯 Exam Tip: For a question on eye structure, focus on the roles and innervation of the six extrinsic eye muscles, as they are key to eye movement and a detailed understanding of the eye's mechanics.

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