Question

Stirred-tank bioreactors have been designed for
a. Availability of oxygen throughout the process
b. Ensuring anaerobic conditions in the cultural vessel
c. Purification of product
d. Addition of preservatives to the product

Answer 1

When an alien DNA is inserted into the cloning vector and then transferred to the host cell, DNA gets multiplied and proteins are formed. To obtain such recombinant proteins on a large scale, bioreactors are needed.

Complete answer:
- A basic stirred-tank bioreactor consists of a large stainless steel vessel around which there is a jacket of circulatory water that controls the temperature within the fermenter.
- It also has an agitator consisting of flat blades that can be rotated with the help of a motor. It ensures the thorough mixing of the contents so that the nutrients mix well. It also prevents the settling out of cells at the bottom.
- It also has adequate arrangements for the aeration, pH and temperature control. The proper aeration is maintained by the process called sparging in which the air is forced into the bottom of the tank through a porous ring called sparger.
- The top of the tank also has a number of inlet tubes called ports through which material can be introduced or withdrawn from the tank.
- The base of the tank has a harvest line for extracting culture, medium and microbial products.
- These are usually costly due to high energy requirements to drive the agitators and introduce the compressed air. These are commonly used in industries for large scale production of antibodies and vaccines.

Hence, the correct answer is option (A).

Note: Such small scale fermenters of 10-100 liters of capacity are used in research labs and they are provided with many controls for the monitoring of physical, chemical and biological parameters that affect the growth of cells.