Q.Justify the statement, "Mitochondria are power houses of the cell".

If a cell were a factory, two rooms would stand out above the rest: the manager's office that gives all the orders, and the power plant that keeps the lights on. In a eukaryotic cell those two rooms are the nucleus and the mitochondria — and comparing them side by side is a great way to see how a cell divides up its most important work.

The nucleus is the control centre. It directs the activities of all the other organelles and carries the hereditary material. It is wrapped in a nuclear envelope — a double membrane pierced by nuclear pores through which RNA and proteins move between nucleus and cytoplasm. Inside sit the chromatin (made of DNA, histone and non-histone proteins, and RNA), which condenses into chromosomes during cell division, and one or more nucleoli, which are the sites where ribosomal RNA is made. In short, the nucleus stores the genetic instructions and runs the cell.

The mitochondria are the power houses. Each is a double membrane-bound organelle: a smooth outer membrane forms the boundary, while the inner membrane is thrown into folds called cristae that increase its surface area, and inside lies the dense matrix. Here aerobic respiration takes place, generating the cell's energy currency, ATP. So the mitochondria supply the power that every other part of the cell depends on.

What makes the pairing genuinely interesting is a feature they share:

• Both are bounded by a double membrane — the nucleus by its nuclear envelope, the mitochondrion by its outer and inner membranes.
• Both hold their own DNA — the nucleus carries the cell's main store of DNA in its chromosomes, while a mitochondrion contains its own single circular DNA molecule. …