Cell is the basic structural and functional unit of organism. As described earlier cell is a self contained unit.
Every cell has the necessary metabolic machinery to meet its requirements. In spite of a great diversity among the living organisms the construction pattern and the metabolic activities of all kinds of cells are remarkably similar.
Components of all kinds of cells are made up of almost of the same six elements (C, H, 0, N, P & S). About 5% of cellular materials also consist of non-metals like chlorine, iodine and metals like calcium, phosphorus, sulphur, potassium, sodium, magnesium and iron, which are known as minor elements. Carbon, oxygen, Hydrogen and Nitrogen are called major elements.
Other non-metals like silicon, boron, fluorine, selenium and metals like copper, zinc, cobalt, molybdenum, chromium and aluminium are present in very small amount and are known as trace elements. All the chemical compounds, ions and elements together constitute the cellular pool.
In the cellular pool, the chemical occur in two phases – aqueous and non-aqueous. In the aqueous phase soluble molecules like sugar, amino acids, fatty acids and inorganic salts form transparent homogeneous solution. Other molecules like starch proteins, nucleic acid etc. form colloidal solution.
The non-aqueous phase contains mainly the organic molecules, such as components of plasma membrane, cell-wall and cell organelles. Depending upon their size, molecular weight and solubility, the constituents of cellular pool are divided into micro molecules and macromolecules.
The micro-molecules are of small size, low molecular weight and high solubility. These include water, minerals, sugars and amino acids. The macromolecules are of larger size, high molecular weight and relatively less solubility.
They are formed by the polymerization of micro molecules. Polysaccharides, lipids, proteins and nucleic acids are the common macromolecules. The cell inclusions or ergastic substances or deutoplasmic substance include the reserve or storage substances, secretary substances and excretory substances.