What is responsible for telling cells how to behave

Its DNA.

Explanation:

The genetic material of which all living beings are created recieves the name of DNA (deoxyribonucleic acid). It is present in living organism cells and it is the one that provides the instructions of what to do to the cell, it gives orders as of when a  cell needs to grow, to do an specific function and how that cell would respond to its environment.

b) the inside picture would look at a very high temperature in a very low ph