SELINA Solutions for Class 10 Biology Chapter 11 - Sense Organs

Page / Exercise

Chapter 11 - Sense Organs Exercise Ex. 1

Solution A.1
(b) Cornea
Solution A.2
(b) Cochlea
Solution A.3
(c) Eustachian tube, tympanum and utriculus
Solution A.4
(a) Retina
Solution B.1

(a) Rhodopsin

(b) Eustachian tube

(c) Hammer

(d) Eustachian tube

(e) Cornea

(f) Auditory nerves

(g) Rods and cones

(h) Hypermetropia

Solution B.2
(a) Cones: Iodopsin:: rods: rhodopsin

(b) Sound: ear drum:: dynamic balance: semi-circular canals
Solution B.3

Column I 

Column II 

(i) The blind spot 

(e) no sensory cells  

(ii) The yellow spot 

(d) maximum sensory cells 

(iii) Ciliary muscle 

(b) shape of the lens  

(iv) Iris 

(a) colour of the eye  

(v) Pupil 

(c) amount of light entering the eye 

 

Solution C.1

(a) False

Correct statement: Deafness is caused due to rupturing of the eardrum.

(b) False

Correct statement: Semicircular canals are concerned with dynamic balance.

Solution C.2

(a) Yellow spot lies at the back of the eye almost at the centre on the horizontal axis of the eyeball. It is the region of brightest vision and also of colour vision.

 

(b) Lacrimal glands are located at the upper sideward portion of the eye orbit. They pour the secretion in the form of tears which serves as a lubricant, antiseptic and even washes away dust particles from the eyes.

 

(c) Organ of Corti is present in the middle cochlear canal of the ear. It helps in hearing.

 

(d) Semicircular canals are located in the inner ear. These help in maintaining the dynamic equilibrium of the body.

 

(e) Oval window is located in the middle ear. It helps in setting the fluid in the cochlear canals into vibration.

 

(f) Utriculus is located in the inner ear. It joins the semi-circular canals to cochlea. It also helps in maintaining static balance of the body.

Solution C.3

(a) Auditory canal, tympanum, ear ossicles, oval window, cochlea

(b) Conjunctiva, cornea, lens, retina, optic nerve

Solution C.4

(a) Cochlea: Cochlea contains organ of Corti which contains sensory cells for hearing. They transmit sound impulses to the brain through auditory nerve.

 

(b) Auditory nerve: It is the main nerve formed by nerve fibres arising from the sensory cells present in cochlea. This nerve carries sound impulses from inner ear to the brain.

 

(c) Retina: It is the innermost layer of eye which is sensitive to light. Retina forms the image of an object seen by the eyes.

 

(d) Choroid: It is middle vascular layer of the eyeball. Choroid provides nourishment to the eye.

 

(e) Sacculus: It is a part of semicircular canals of the inner ear. It contains sensory cells called macula which help in static balance of the body when it is a stationary position. 

Solution C.5

Structure 

Function 

Auditory nerve 

Transfers impulse from inner ear to brain 

Ciliary muscle 

Helps to change the focal length of the eye lens 

Semicircular canals 

Dynamic equilibrium 

 

Solution C.6

(a) Rhodopsin and iodopsin.

(b) Dark adaptation and light adaptation.

(c) Distant vision accommodation and near vision accommodation.

(d) Sclera, choroid and retina. 

Solution C.7

Cause

Eye defect

(a) Lens turns opaque

Cataract

(b) Uneven curvature of the cornea

Astigmatism

(c) Deficiency of vitamin A

Night blindness

(d) Lens loses its flexibility

Presbyopia

(e) Eye ball lengthens from front to back

Myopia

(f) Lens becomes too flat

Hyperopia

 

Solution D.1

(a) Conjunctiva: A thin membrane covering the front part of the eye is called conjunctiva.

 

(b) Macula lutea: Macula lutea or yellow spot is a point in the centre of the retina where rods and cones are highly concentrated which offers brightest vision.

 

(c) Adaptation: Adaptation is the ability to adjust vision in bright and dark areas.

 

(d) Ampulla: Ampulla is the swollen wide part of each semicircular canal which contains sensory cells called cristae which help in dynamic equilibrium or dynamic balance of the body when it is motion. 

Solution D.2

(a) Differences between myopia and hyperopia (type of lens used for correction):

Myopia

Hyperopia

Myopia can be corrected by suitable concave (diverging) lens.

Hyperopia can be corrected by suitable convex (converging) lens.

 

(b) Differences between rods and cones (sensitivity):

Rods

Cones

Rods are sensitive to dim light but do not respond to colour.

Cones are sensitive to bright light and are responsible for colour vision.

 

(c) Differences between aqueous humour and vitreous humour (location):

Aqueous humour

Vitreous humour

Aqueous humour is the front chamber between the lens and the cornea.

Vitreous humour is larger cavity of the eyeball behind the lens.

 

(d) Differences between near and distant accommodation (shape of lens):

Near accommodation

Distant accommodation

For near accommodation, the lens becomes more convex or rounded.

For distant accommodation, the lens is more flattened or thinner.

 

(e) Differences between dark and light adaptation (pigments which will be regenerated):

Dark adaptation

Light adaptation

For dark adaptation, visual purple or rhodopsin pigment will be regenerated.

For light adaptation, visual violet or iodopsin pigment will be regenerated.

 

(f) Differences between night blindness and colour blindness (sensory cells which cannot function properly):

Night blindness

Colour blindness

In night blindness, the rod cells cannot function properly.

In colour blindness, the cone cells cannot function properly.

 

Solution D.3

(a) Sometimes medicines dropped into the eyes come into the nose and even throat because the nasolacrimal duct conducts the secretion into the nasal cavity.

 

(b) Three small bones of ear ossicles transmit the vibrations received by the tympanum and amplify them. If these were replaced by a single bone, the vibrations received by the tympanum would not be amplified. Hence, three small bones of ear ossicles are advantageous as compared to one single bone for hearing.

 

(c) There are no sensory cells in the blind spot and therefore, this is considered as 'area of no vision' and image striking it cannot be perceived.

Solution D.4

(a) The process of focusing the eye at different distances is called the power of accommodation. The ciliary muscles are responsible for the power of accommodation.

 

(b) The image formed on the retina is inverted and real.

Solution D.5

While reading a book, the lens is more convex or rounded due to contraction of ciliary muscles because the book is usually read from a short distance. When we raise our head and look at a distant object, the ciliary muscles relax to build the tension on the suspensory ligament so that they can stretch the lens. This change in the curvature of the lens makes us focus on distant object.



Solution D.6

If we look at a bright object and then close our eyes, the sensation of light persists for a short period. This is known as persistence image or the after image. It lasts for one-tenth of a second. Therefore by closing the eyes and gently pressing them with your palms, you see some specs of brilliant light.

Solution D.7
The three ear ossicles are: Malleus (hammer), Incus (anvil) and Stapes (stirr up).

The last ear ossicle, stapes, vibrates and transmits the vibration to the oval window.

The role of other two ear ossicles is to magnify the vibration of stapes as a result of their lever like action.
Solution E.1

a. Shape of the eye:

 Near vision - flattened

 Distant - rounded or more convex

 

b. Ciliary muscles and suspensory ligament

 

c. In the dark: Cells - rod cells, Pigment - rhodopsin

In the light: Cells - cone cells, Pigment - iodopsin

Solution E.2

a. The middle ear or membranous labyrinth has two structures inside it, the cochlea and the semi-circular canals.

b. Static balance - Utriculus and sacculus (inner ear)

Hearing - Internal ear

Dynamic balance - Semi-circular canals (inner ear)

c. Collectively they are termed as ossicles.

Solution E.3

(a) 1 - Aqueous chamber, 2 - Lens, 3 - Iris, 4 - Cornea, 5 - Conjunctiva, 6 - Sclera, 7 - Choroid, 8 - Retina, 9 - Yellow spot, 10 - Optic nerve (Blind spot)

 

(b) Part 3 (Iris) - It contains radial muscles to dilate the pupil and circular muscles to constrict the pupil.

Part 7 (Choroid) - It is the middle layer of the eyeball, richly supplied with blood vessels and provides nourishment to the eye.

 

(c) Part 9 (yellow spot) contains sensory cells especially the cone cells while part 10 (blind sport) contains no sensory cells.

 

(d) Part 6 (sclera) gives shape to the eyeball and part 8 (retina) acts as screen to form image of an object. 

Solution E.4

(a) Myopia

(b) The two possible reasons for myopia are either the eye ball is lengthened from front to back or the lens is too curved.

(c) 1 - vitreous humour, 2 - blind spot, 3-lens, 4-pupil

(d) Concave lens

(e)

Solution E.5

(i) Ear

(ii) m - malleus, i - incus and s - stapes respectively. These are collectively called as ear ossicles.

(iii) Cochlea. The vibrating movements in the hair of the sense cells of cochlea transmit the impulse for hearing to the brain via auditory nerve.

(iv) Tympanic membrane. It vibrates and then sets the ear ossicles into vibration in the process of hearing.

Solution E.6

(i) Ear ossicles

(ii) A - Cochlea, B - Semicircular canals, C - Ear ossicles

(iii) Cochlea helps in transmitting impulses to the brain via the auditory nerve. Semicircular canals help in maintaining dynamic equilibrium of the body.

(iv) Organ of Corti

Solution E.7

 

 

Utriculus and Sacculus are responsible for maintaining static balance in human beings.

Solution E.8

(a) Myopia

(b) A-Normal eye, B-Myopia

(c) Looking glasses with the concave lens are required here.

Solution E.9

(a) 1 - External ear (pinna), 2 - Ear drum (tympanum), 3 - Auditory canal, 4 - Malleus, 5 - Semicircular canals, 6 - Cochlea, 7 - Auditory nerve, 8 - Eustachian tube.

 

(b) Part 6 (Cochlea) - It contains sensory cells for hearing.

Part 7 (Auditory nerve) - It transmits impulse of hearing to the brain.

Part 8 (Eustachian tube) - It equalizes air pressure on both the sides of the tympanum.

 

(c) It is harmful to use a sharp object to remove ear wax as it can rupture the ear drum.

The part involved is part 2 - Ear drum (tympanum).