Question

(a)Have you ever thought how do you feel the climatic changes in the environment?

(b)How do you see an object and its colour?

(c)How do you hear a sound?

Answer 1

(a)
Part 1: Introduction
We humans are able to touch,smell,hear, taste primarily because of our sense organs.Given below are the sense organs in human beings:
Sense of sight- Eye
Sense of hearing- Ear
Sense of smell- Nose
Sense of taste- Tongue
Sense of touch- Skin
These senses are perceived by means of various sensory structures. It helps an organism to respond to stimuli, gather and process the information about the changes in its immediate environment.
For example -to perceive the sense of hearing sensory organ ear receive the respective stimuli and help generate the appropriate response.

Part 2: Detection of environmental changes

• Skin is a sense organ responsible for sensation of touch, heat, cold etc.
• Skin has thermoreceptors that receive different stimuli related to touch, temperature, pain etc.
• If there is any climatic change (change in temperature) in an environment, it will be sensed by the receptors of skin and sent to the brain.
• In the brain this information will be processed and an appropriate response will be given.

(b)
Part 1: Mechanism of vision

• Light rays of visible wavelength enter the cornea & lens and are focused on the retina.
• Photoreceptors in the retina are composed of opsin & retinal, In dark, retinal and opsin interact with each other.
• Light induces the dissociation of retinal and opsin from each other causing a change in the structure of opsin/
• This further causes change in the permeability of the membrane.
• Change in permeability generates an action potential which is transmitted by optic nerves to the visual cortex area of the brain.
• These impulses are analysed & an image is formed on the retina which is recognised on the basis of earlier memory & experience.

Part 2: Colour vision

• Retina has cone cells which help in the colour vision.
• There are three types of cones found in the human eye, namely, red, green and blue cones.
• Each type of cone is sensitive to a particular wavelength of light.
• When light of different wavelengths stimulates more than one type of cone cells simultaneously, it results in the detection of different colors.

(c)
Part 1: Mechanism of hearing
We hear sound due to the presence of the ear (a sense organ) which is sensitive to sound.

• The pinna of the external ear collects sound waves which pass through the external auditory meatus all the way to the eardrum.
• These vibrations are passed from the eardrum to the malleus, incus and stapes of the middle ear which causes an increase in the frequency of the vibrations.
• The vibrations furthermore are passed to the cochlea of the inner ear through the oval window.
• These vibrations in the endolymph of the cochlea cause vibrations to be induced in the basilar membrane, which in turn cause the sensory hair of the organ of corti to vibrate.
• The receptor hair cells force themselves against the tectorial membrane, converting sound energy to a nerve impulse or action potential.
• This nerve impulse is transmitted to the auditory cortex of the brain, where the impulse is evaluated and analyzed causing the sound to be recognized.