A typicl cell has rwo major parts are the nucleus and the cytoplasm.The different substances that make up the cell are collectively called protoplasm.Protoplasm is composed mainly of five basic substances:water,electrolytes,proteins,lipid,and carbohydrates.

Water:water is the principle fluid medium of the cell,which is present in more cells except fat cells,in a cocentration of 70 to 80%.Many cellular chemicals are dissolved in water.

Ions:The most important ions are in the cell are potassium,magnesium,phosphate,sulfate,bicarbonate and smaller quantities of sodium,chloride and calcium.The ions are responsible for cellular control mechanisms.For instance,ions acting at the cell membrane are required for transmission of electrochemical impulse in nerve and muscle fibers.

Protien:After water themost abundant substances in most cells are proteins,which normally constitute 10 to 20 per cent of the cell mass.These can be divided into two parts: structural protein and functional proteins are present in the form of long filaments.These filaments remain in the form of microtubules that provide the "cytoskeleton" of such organelles as cilia,nerve axons,the mitotic spindle of mitosing cells.

The functional proteins are an entirelydifferent type of protein,usually composed of combination of a few molecules in tubular-globular form. Lipid:Lipid are several types of substances that are grouped together because of their common property of being soluble in fat solvents.Important lipids are phospholipids and cholesterol.

The additional phospholipids and cholesterol,some cells contain large quantities of triglycerides.The fat stores in these cells represents the body's main storehouse of energy giving nutrientsthat can later be solute and used to provide energy wherever in the body is needed.

Carbohydrates: Carbohydrates play a major role in nutrition of the cells.Carbohydrates in the form of dissolved glucose is always present in the surrounding extracellular fluid .Also a small amount of carbohydrates is virtually always stores in the cells in the form of glycogen and used rapidly to supply the cell's energy needs.