Which of the following methods are collectively referred to as downstream processing?

Explain $PCR$ in short.

Refer to the following statements for agarose-gel electrophoresis:
$(a)$ The $\text{DNA}$ fragments resolve according to their size.
$(b)$ The separated $\text{DNA}$ fragment can be visualised only after staining with ethidium bromide followed by exposure to $UV$ radiation.
$(c)$ $\text{DNA}$ is always loaded into the well.
$(d)$ The smallest fragment of $\text{DNA}$ is near the well.
Choose the correct statements:

Having become an expert on gel electrophoresis,you are asked to examine a gel for a colleague. Where would you find the smallest segment of $DNA$?

Consider the following figure of a stirred-tank bioreactor and identify $A, B, C$,and $D$.

When a protein-encoding gene is expressed in a heterologous host, it is called a: