Why is the plasma membrane called a selectively permeable membrane ?

What would happen to the life of a cell if there was no Golgi apparatus ?

Carry out the following osmosis experiment :

Take four peeled potato halves and scoos each one out to make potato cups. One of these potato cups should be made from a boiled potato. Put each potato cup in a trough containing water. Now,

$(a)$ Keep cup $A$ empty

$(b)$ Put one teaspoon sugar in cup $B$ 

$(c)$ Put one teaspoon salt in cup $C$

$(d)$ Put one teaspoon sugar in the boiled potato cup $D$.

Keep these for two hours. Then observe the four potato cups and answer the following :

$(i)$ Explain why water gathers in the hollowed portion of $B$ and $C$.

$(ii)$ Why is potato $A$ necessary for this experiment ?

$(iii)$ Explain why water does not gather in the hollowed out portions of $A$ and $D$.

Make a comparison and write down ways in which plant cells are different from animal cells.

Who discovered cells, and how ?