The correct answer to this question is this one: they lacked oxygen. The earliest organisms were completely heterotrophic in nature because of the reason that they lacked oxygen. <span>A heterotroph is an organism that cannot fix carbon and uses organic carbon for growth. </span>
That organisms are called CONSUMERS...
The role of DNA in all cells is to produce molecules of RNA that are involved in protein synthesis. Through the proteins, all the metabolism of the cell is controlled. DNA is also used to synthesize new DNA for daughter cells.