If DNA has only four nitrogen bases, how are organisms so complex within a species?

Nucleic acids, and DNA in particular, are key macromolecules for the continuity of life. DNA bears the hereditary information that’s passed on from parents to children, providing instructions for how (and when) to make the many proteins needed to build and maintain functioning cells, tissues, and organisms.

How DNA carries this information, and how it is put into action by cells and organisms, is complex, fascinating, and fairly mind-blowing, and we’ll explore it in more detail in the section on molecular biology. Here, we’ll just take a quick look at nucleic acids from the macromolecule perspective.

the correct answer is:

a population changes in response to a change in the environment.