The protoplasm outside the nucleus is called cytoplasm. In some cells e.g. Amoeba, the cytoplasm has two distinct parts and outer clear ectoplasm and an inner granular endoplasm in most cell. Under the light microscope cytoplasm appears as a semi fluid colloid that fills the cell. The cytoplasm exhibits active streaming movements around the inner surface of the cell. This movement is known as cyclosis.
Cytoplasm is composed of several types of organelles occupying as much as half of the volume of the cell and a fluid matrix, the cytosal. Cytosal is watery solution of salts, sugar, amino acids, Proteins, fatty acids, nucleotides and other material. Giving shape and organisation to the cytoplasm it is the network of Protein fibres, the cytoskeleton s. many of them organelles and individual molecules of the cytoplasm are thought to be attached to cytoskeletion observation under electron microscope however reveal that cytoplasm not a simple colloid since it contains many different kinds of minute organelles are also a mesh of tiny filaments, the microfibrils that form a sort of skeleton giving rigidity to cell and helping unicellular organisms in movement.
A variety of cytoplasmic organelles are present in cells, majority of them are on the basis of membrane.
Membrane bound organelles:
(i) ENDOPLASMIC RETICULUM
It extends from plasma membrane to the nuclear membrane. It is an elaborate tube like system of lipoprotein.
They appear to be associated with enzyme formation, proteins synthesis, storage and transport metabolic products. They may also contribute to the formation of cell plate in nuclear division and of the nuclear membrane around the newly formed nuclei.
(ii) MITOCHONDRIA
They appear as minute granular vesicles, rodlets, threads or strings. They are the centre of aerobic respiration. They are called power house of the cell.
(iii) GOLGI APPARATUS (DICOTYOSOME)
This was found by scientist golgi and was names as Golgi body. Each of them is disc shapedand ahs central, flattered, plate like cisternae, peripheral network interconnecting tubules and peripherally occurring vesicles and golgian vacuoles.
(iv) PLASIDS
They are protoplasmic membrane bound organelles which function as chemical synthesizers and storage bodies. They occur in great number in the cell of plants.
Non-membrane bound organelles
(i) RIBOSOMES
They contain high concentration of Ribonucleic acid (RNA). Ribosomes are associated with the membrane of the tubes and also occurring free in the cytoplasm and are very small particles. They synthesize some of the enzymes and are mainly concerned with protein synthesis.
(ii) CENTRIOLE
In the cytoplasm near nucleus the cells of certain lower plants possess centriole. Higher plants generally lack centiole. Each centrosome consists of two cylinders called centriole lying perpendicular to one another. Each cylinder is composed of nine parallel triplets of hollow cylindrical microtubules. During cell division the centriole replicates and moves to opposite side of the cell and thread like fibres begin to radiate from centriole in all directions called astrial rays.
(iii) VACUOLES
They are non-protoplasmic liquid filled cavities in the cytoplasm and are surrounded by a membrane called tonoplast. It is permeable and allows certain substances to enter in the vacuole. They are more prominent in nature cells. Vacuoles in plant cells are filled with cell sap and act as store house which often play role in plant defence which is necessary for plant cell enlargement.
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