1. Give reasons:
a) A de-shelled egg is placed in pure water, after 5 minutes it swells.
b) When placed in hypotonic solution for a very long time, an animal cell bursts but a plant cell does not.
c) Mitochondria and chloroplasts can synthesize their own proteins.
d) In the laboratory, after removing the onion peel, it should immediately be transferred to water.
e) Plasma membrane is known as selectively permeable membrane
Answers
(a) A deshelled egg has lesser concentration of water inside when compared to the outside of the egg. As a result, endosmosis occurs and the cells shrink, resulting in the overall shrinkage of the egg after some time.
(b) In a hypotonic solution, the animal cells burst as the contents of the cell exert pressure on the cell membrane, which is not able to bear that pressure and bursts. But in a plant cell, the cell wall is present which exerts an equal pressure on the conte and prevents the cell from bursting.
(c) Mitochondria and Chloroplasts are unique cell organelles with their own ribosomes and DNA. They are independent and can synthesise their own proteins.
(D) This is done because the onion peel (Epidermis) may dry up or get folded. This results in inappropriate mounting of the peel on the glass slide of the microscope. The epidermis needs to be flat and smooth in order to be observed.
(E) Plasma membrane allows only a particular substances to enter and exit the cell. So, it is known as a selective permeable membrane.
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