State the reason for the following:
$(i)$ Mitochondria are known as the powerhouse of the cell.
$(ii)$ Plastids are able to make their own protein.
$(iii)$ Plant cells shrink when kept in a hypertonic solution.

(N/A) $(i)$ Oxidation of food takes place in mitochondria,and they release energy in the form of $ATP$. This energy is required for various chemical activities essential for life. Hence,mitochondria are known as the powerhouse of the cell.
$(ii)$ Plastids contain their own $DNA$ and ribosomes. Therefore,they are capable of synthesizing their own proteins.
$(iii)$ $A$ hypertonic solution has a lower water concentration than the cytoplasm of the cell. When a plant cell is placed in such a solution,water moves out of the cell due to the process of exosmosis,causing the cell to shrink.