Answer:
(d) Each cell is bounded by an extremely delicate,
thin elastic living membrane, called the plasma membrane. The plasma membrane
is made up of two layers of lipid (fat) molecules with protein molecules which
is sand witched between lipid layer.
The structure of plasma membrane can be observed under an
electron microscope only. It is a selectively permeable membrane which allows
the flow of only some substances into the cell and out of the cell. Viruses do
not have any membranes.
Functions
1. It gives a definite shape to the cell.
2. It provides protection to the in contents of the cell.
3. It regulates entry and exit of substances in to and out
of the cell.
4. It can internalize solid and liquid materials by in folding
or extending around them.
This is the process of active intake of materials,
5. In animal cells, it is involved in adhesion,
recognition and in the formation of vesicles, cilia, flagella, microvilli etc.
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