Write short notes on
(a) Mitochondria;
(b) Plastids.
(a) The mitochondria are tiny bodies of varying shapes and size. Each mitochondria is bounded by a double membrance envelope. Outer membrane is porous. The inner membrane is thrown into folds. These folds are called cristae and are studded with small rounded bodies known as F1 particles or oxysomes. The interior cavity of the mitochondria is filled with a proteinaceous matrix which contains a few small-sized ribosomes, a circular DNA molecule and phosphate granules. Mitochondria are sites of cellular respiration.
(b) Plastids occur in most plant cells and are absent in animal cells. They have their own genome and ribosomes. There are three types of plastids : chromoplasts, chloroplasts and leucoplasts.