When microorganisms are cultured for desirable products in the laboratories the quantity of produce is fairly low and cannot meet the high market demand. Thus, to meet the market demands when the desired products are produced in an industrial scale in the bioreactors the yield is much higher. In industries these cells are allowed to multiply in a continuous culture system where the used medium is drained out from one side while fresh medium is added from the other to maintain the cells in their exponential phase. Thus bioreactors can be defined as large containers in which raw materials are biologically converted to specific desired products such as enzymes, hormones, antibodies, etc., using microbial, plant, animal or human cells. A bioreactor provides optimum growth conditions including temperature, pH, substrate, salts, vitamins, oxygen, etc., and even mixing if needed to achieve its desired product.

Note: Exponential phase of a cell is the most metabolically active phase of any cell where it utilises high amount of substrate and grows and divides at a higher rate.