Answer:
The cells get all the required micro and macro nutrients from the medium in which it is kept for growing. The nutrient media is prepared in such a way that it contains all the required elements in adequate amount.
The cells inside the medium has amino acids, oxygen, air in it which is used by the cells for their growth.
The cells on growth produces the desired product which is then extracted from the bioreactor.
The purification of product is done by its bio processing and in this way the desired product in a purified form is obtained.