Sslc biology chapter2 notes |windows of knowledge

Kerala pareeksha bhavan decided to conduct sslc public exam 2023 on march.Here we are discussing Sslc biology chapter2 notes from chapter windows of knowledge

Feelings are possible by impulses from different sense organs reach at the brain through different sensory nerves.our sense organs include Eyes, Ears, Nose,Tongue & Skin

Sslc biology chapter2 notes about EYES

  • Eye :
    • Function: vision.
    • Protection:eyes are protected in Bony eye socket called orbit. External eye muscles gives support to this
    • Eyelids,Eyelashes &Eyebrow have various function
    • Tears cleans&lubricate the front part, washes away the materials particles.For destroy ing germs tears contains an enzyme called lysozyme
    • Conjunctiva it secretes mucus to prevent the eye from being dry.
  • The 3 layers of human eye ?
    • a. Sclera –The outermost layer, that gives firmnessto eye. Its transparent anterior portion is the cornea. Conjuctiva covers anterior part of sclera,excluding cornea.
    • b.Choroid- It is middle layer contains blood capillaries, suppies nutrients & oxygen. Its anterior dark screen with pupil is the iris. The pigment, melanin gives colour to iris.A convex lens, which is connected to ciliary muscles by ligaments, is placed behind the iris.
    • c. Retina- The inner layer on, images are formed here. Retina contains photoreceptors (cone cells and rod cells). Yellow spot which contains
  • plenty of photoreceptors is the point of maximum visual clarity and the blind spot where no photoreceptors seen due as the begininng of optic nerve is the point of no vision. The sensory optic nerve starting from retina.

The fluids filled in the chambers of eye ?

  • Aqueous humor – It is watery fluid seen in the aqueous chamber,which is between the cornea and lens.It formed from the blood. Acques humor fluid supplies nutrients and O2(oxygen) to cornea and lens.
  • Vitreous humor – It is jelly like fluid of the vitreous chamber .Vitreous chamber is found in between lens and retina.By the help of this eyeball maintain its shape

  • Radial muscles and circular muscles are found in the iris regulate the size of pupil according to the light intensity.
  • In dim light, radial muscles contracts& increases it’s size
  • In intense light, circular muscles contracts & decrease the size of pupil.
  • Ciliary muscles adjust the curvature of eye lense and there by adjusting focal length.
  • While seeing near objects, ciliary muscles contract to increase the curvature of lens-decreases the focal length.
  • While viewing far objects, ligaments stretch to relax the ciliary muscles and curvature of lens decrease to increase the focal length .

Colour vision is provided through cone cells,which are 3types (red, green & blue)
Retinal is one of visual pigment found in the photoreceptors that is formed from vitamin A.
Under dim light -rhodopsin splits to form retinal and opsin to produce impulses .
Under intense light-photopsin (iodopsin) splits to form retinal and opsin to produce
impulses.After that impulses are transmitted through the optic nerve to the brains crebrum. Thus vision made possible.

Experiencing of vision :

Image appears on retina – stimulation of the photo receptors – dissociation of rhodopsin / photopsin
– impulses form – optic nerve – coordination of images by cerebrum – perfect vision.
Binocular vision is the ability of two the eyes to focus on same object to get perfect image when brain combines these images. This help us to get a 3d vision image of the object and by this we can calculate the correct distance,depth,height and width of the object.

Defects and diseases of eyes :

  1. Hyper metropia also known as long sight: the person can’t see near-by objects clearly due to shortened eyeball.
  2. Myopia also known as short sight:The person Can’t see far objects clearly due to elongated eyeball.
  3. Night blindness : the person can’t get clear vision in dim light due to vitamin A deficiency
  4. Colour blindness :The person Fails to detect colours like red or green colours due to defects in red cone cells and green cone cells.
  5. Xerophthalmia : In this patients conjunctiva and cornea become dry & opaque due to long-term deficiency of vitamin A.
  1. Cataract : Eye Lens become opaque-the person become blind
  2. Glaucoma : In this situation re-absorption of aqueous humor obstructed by pressure inside the eyes increases,resulting damage to eyes retina and photoreceptors of eyes. By this person become blind
  3. Conjunctivitis : Infection of bacteria or virus causes red eye with pain Points related with the health of our eyes.


  • Ear : for hearing and body balance.
  • Main parts:
    • a. External ear : Pinna, auditory canal and tympanum.
    • b. Middle ear : Ear ossicles,bones of middle like malleus, incus, stapes and eustachian tube.
    • c. Internal ear : Cochlea, Auditory nerve, Vestibule, semicircular canals and vestibular nerve.Oval window and round window.
  • Fluids inside the internal ear :
    Endolymph and perilymph.

  • Pharynx; It protects tympanm by balancing the pressure on either sides of it.
  • Ear ossicles malleus, incus, stapes amplifies and transmit the vibrations of tympanum to internal ear.
  • Oval window attached with stapes, speed up the vibrations of ear ossicles(malleus,incus,stapes) to internal ear.
  • The internal ear, constitutes membraneous labyrinth, seen inside a bony labyrinth. A coiled tube like cochlea, auditory nerve,
  • thevestibular apparatus (vestibule & 3 semi- circular canals) and vestibular nerve are the
    parts of internal ear.
  • The membraneous labyrinth is filled with a fluid known as endolymph and the space between the bony labyrinth and membraneous labyrinth is filled with another fluid, named perilymph.
    The part,cochlea functions in hearing,
  • Vestibular apparatus helps to maintain body balance through transmitting impulses to the cerebellum.Auditory receptors – hair cells seen in the
  • Organ of Corti of cochlea. Sensory hair cells are also seen in the vestibule and semicircular canals.

Hearing. (Flowchart).

Sound waves — ear pinna – auditory canal – tympanum vibrates – ear ossicles amplify it –
oval window – cochlear perilymph vibrates — endolymph vibrates – stimulation in auditory receptors (hair cells) of the basilar membrane of Organ of Corti – impulse form — auditory nerve – auditory centre of the brain – hearing.

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Role of ear in maintaining the equilibrium :

Auditory receptors- hair cells seen inside the vestibule and semicircular canals stimulated according to the movement of head.Then the impulses formed are transmitted to the cerebellum through the sensory nerve- vestibular nerve. Cerebellum functions so as to maintain the equilibrium of body.

C.Sense of Taste

C. Sense of Taste : Chemoreceptors seen inside the mouth and tongue help us to detect taste. They
seen inside the papillae of the tongue are the taste buds.
The different taste buds of the tongue include Sweet, salt, sour, bitter, umami etc.When substances dissolve in saliva, chemo- receptors in the taste buds stimulate and impulses reach the brain through the respective nerves. Then we experience taste.

D. Sense of Smell

D. Sense of Smell : by the olfactory receptors in the mucus membrane. When aromatic particles dissolve in the
mucus, the olfactory receptors get stimulate and the impulses reach the brain through the olfactory nerve. Brain helps in feeling smell.

E. Skin : has receptors fto sense Temperature, Cold, Touch, Pressure and Pain.

F. Receptors in a few organisms :

  • Eye spot in Planaria – to detect light)
  • Ommatidia (cluster of photoreceptors in housefly)
  • Jacobson’s organ in snake-(to detect smell
  • Receptors in the Lateral line of shark -to detect changes in the balancing of body
    Olfactory receptors in shark are highly sensitive.

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