The Protoplasmic mass of the cell leaving out the nucleus and the plastids is call cell protoplasm or cytoplasm. When the cell is young to cytoplasm completely fills its cavity i.e. the space between the cell wall and the nucleus. As the cell repidly increases in size it cannot keep peace with the growth of the cell wall. Consequently a number of small non protoplasmic cavities appear in the cytoplasm which are called vacuoles. As the cell further increases in size and matures all these small vacuoles fuse together into a large one which then occupies the greater part of the cell pushing the cytoplasm outwards as a thin living layer against the cell wall.
In some cells comparatively small vacuoles persist and then the cytoplasm forms delicate strands around them. The vacuole is filled with a fluid called cell sap which is water containing a large number of soluble chemical substances such as inorganic salts, organic acids, soluble carbohydrates e.g. sugar, soluble proteins, amino acids and in certain cells, nucilage, anthocyanins, tannins, latex, alkaloids etc in varying proportions. The vacuole is thus a tiny reservoir of the cell from which the cytoplasm draws water and other material according to its need.
They cytoplasm has three distinct parts (1) its outer surface forms an extremely thin and delicate membrane called plasma membrane or ectoplasm. (2) Its middle part is granular and is called the endoplasm; its fluid portion is called hyaloplasm and (3) its innermost part surrounding the vacuole as a thin membrane is called the vacuole membrane of tonoplasm. The ectoplasm controls the entrance and exit of water and many chemical substances into and out of the cell, the tonoplast does the same in respect of the vacuole, while the endoplasm performs the general function of the cytoplasm. The membranes are hyaline in nature and are made up of lipoproteins. Cytoplasm includes various substances like plastids, endoplasmic reticulum, ribosomes chondriosomes, golgi bodies, centrosomes and ergastic substances.
Kolliker in 1862 gave the name cytoplasm to the substance found around the nucleus. The cytoplasm usually consists of water which may be 85 to 90 percent in it. Many organic and inorganic substances also occur in the cytoplasm either in true solution or in colloidal state. Salts, carbohydrates and other water soluble substances are found in dissolved state. Proteins and fats are also found in the form of very minute particles which are invisible in the microscope of ordinary light. They are found in colloidal state. The cytoplasm remains always in dynamic state due to constant phase inversions. It is bounded by a non molecular or multi-molecular layer on the outside called ectoplasm or plasma membranes while the layer on inside called tonoplast or the vacuolar membrane. The protoplasmic layers are semi permeable in nature which involve in differential absorption. In the cytoplasm the fatty substances such as lipids and certain proteins take part in the formation of plasma membrane. The vacuolar membrane also develops from the same substance and possesses similar structure to that of plasma membrane.
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