Q1 of 102 Page 127

State the functions of the following:

(i) Eyelids ………………………………………


(ii) Eyelashes ………………………………………


(iii) Tears ………………………………………


(iv) Iris ………………………………………


(v) Ciliary muscles ………………………………

(i) Eyelids: They protect the front of the eyes and shut out the light entering into the eye.


 


(ii) Eyelashes: They prevent the falling of large particles into the eye.


 


(iii) Tears: Tears help in washing away the dust particles in our eye.


 


The labelled diagram of the eye is shown below:


 



 


(iv) The thin and circular iris of the eye is responsible for controlling the diameter and size of the pupil and thus, the amount of light reaching the retina.


 


(v) The ciliary muscle fibers in the eyes enable change in the lens shape for focusing light falling on the eyes.


 































Parts of eye




Function




(i) Eyelids




The upper and lower movable eyelids protect the outer surface of the eyes by shutting out light and other dust particles. The eyelids contain flexible muscles that naturally shut down on seeing a foreign particle approaching close to the eyes in order to protect it from being hurt.




(ii) Eyelashes




The hair of the eyelashes helps trap the dust particles that come close to the eyes. This prevents any infection in the eyes that can be caused due to various dust particles




(iii)Tears




Tears act as a lubricant on being spread by the eyelids. It keeps the front portion of eyes clean by washing away dust particles. Tears also have an antiseptic property due to having lysozymes which kill germs.




(iv) Iris




The thin and circular iris of the eye is responsible for controlling the diameter and size of the pupil and thus, the amount of light reaching the retina.




(v) Ciliary muscles




The ciliary muscle fibers in the eyes enable change in the lens shape for focusing light falling on the eyes.



 

More from this chapter

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2

Given below are a few situations. What effective change will occur in the organ/body part mentioned and which part (sympathetic or parasympathetic) of the autonomic nervous system brings it about?













































Situation



Organ/Body part



Change/Action



Part of autonomic nervous system involved



1. You have entered a dark room



Eye



………….



………….



2. Your body is consuming lot of glucose while running a race



Liver



………….



…………



3. You are chewing a tasty food



Salivary gland



……………..



…………



4. You are running a race



Adrenal gland



………………



…………..



5. You are retiring to bed for sleep



Heart



……………



…………



6. You are shivering in intense cold



Body hairs



………….



…………






 3

Given below is the partially incomplete scheme of the components of the peripheral nervous system. Fill up the blanks numbered (1)-(8):

 2

Write in proper sequence the names of all the parts of the human eye through which the light rays coming from an object pass before they form an image on the retina.

 3

Name the following:

(i) Place of best vision in the retina of the eye __________________


(ii) Place of no vision in the retina of the eye __________________


(iii) Kind of retinal cells sensitive to dim light __________________


(iv) The circular opening enclosed by iris __________________


(v) The fibers which collectively hold the lens in position __________________


(vi) The capacity of the eye to focus at different distances __________________


(vii) The kind of lens required to correct nearsightedness __________________


(viii) The layer of the wall of the eye-ball that corresponds to the black lining of the box of a camera __________________