(1) Mitochondria: These are small rod-shaped organelles. Each mitochondrion is bounded by a double membrane. The outer membrane provides a smooth, uninterrupted boundary to the mitochondrion. The inner membrane is raised up into a large number of finger-like projections, called cristae, towards the interior of the mitochondrion. The interior is known as matrix. Matrix is filled with semi-liquid fluid. In a matrix and on the inner side of it, many enzymes are present, which control and regulate the release of energy during oxidation of food molecules, in respiration.
Function: Mitochondria is the site of respiration. Energy is released during oxidation of food, in the form of chemical energy, stored as ATP molecule(s). This energy can be used by the cell to carry out its various activities. That is why mitochondria are the powerhouse of a cell.
(2) Ribosomes: Ribosomes are small, dense, rounded and granular particles, made up of RNA, proteins, and remain with the membrane of the endoplasmic reticulum. They may occur free, in cytoplasm also.
Function: The main function of ribosomes is to synthesise protein and it regulates the protein synthesis.
(3) Lysosomes: Lysosomes are rough, spherical sac-like structures, bounded by a single membrane. They are filled with dense liquid. The liquid mainly consists of enzymes, which help in the digestion of food molecules.
Functions:
1. They control the digestion of cells.
2. They help in the digestion of dead cells and disintegration cells.
3. They are more in number, in white blood corpuscles. That is why they are capable of digesting the microbes or bacteria.
(4) Endoplasmic reticulum: They were discovered by Keith Porter. These organelles are found in eukaryotic cells. These organelles are not found in prokaryotic cells and in red blood corpuscles of mammals.
These are of two types:
(i) Smooth endoplasmic reticulum: Ribosomes are not found on their outer surface. These are found mainly in those cells which synthesise and store carbohydrates, fats, steroid hormones and other products, devoid of proteins.
(ii) Rough endoplasmic reticulum: Ribosomes are stuck firmly on their outer surface.
Functions of endoplasmic reticulum:
1. They transport different soluble materials inside the cell.
2. They are helpful in the synthesis of protein and steroid hormones.
3. They manufacture the nuclear membrane and golgi bodies.
