Biology XII Notes for Biology Notes

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Cell Organelles: They are the living, sub-cellular bodies of cytoplasm which have definite shape and size and are specialized for particular functions. For e.g. mitochondria, chloroplast, golgi bodies etc.

Ultra structure of Mitochondria:
Mitochondria, known as “the power house of cell”, was first of all observed by Kolliker and named by Benda. Mitochondria are the largest cell organelles in animals. The ultra structure of mitochondria is briefed below:


Mitochondria consist of two membranes and two chambers- outer and inner. Outer membrane is smooth while the inner membrane has many infoldings called as cristae that increase the physiologically active area.
The inner side of inner membrane bears a tennis racket like bodies called oxysomes or F1 particles consisting of a head, a stalk and a base. ATPase, an enzyme necessary for the formation and breakdown of ATP, is present in the head. Inner chamber contains a gel like substance called matrix. The matrix contains – 70s type of ribosomes, proteins, a double stranded circular naked DNA, amino and fatty acids etc.

Functions of Mitochondria:

There are different functions of mitochondria some of which are mentioned below:
1) Primarily, a mitochondrion generates energy in the form of ATP, therefore is called “the power house of cell”.
2) It regulates the calcium ion concentration of cell.
3) It provides the intermediates for the synthesis of chlorophyll, steroids etc.
4) They form the middle piece of sperm.
5) They help in the yolk formation during the ovum formation.

Note: The question- “describe the ultra structures and functions of mitochondria (or any other cell organelles) “is often asked from this unit (in 3 marks).

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