Old existing cells.......
If no oxygen is available to a cell, then the net atp productiion resulting from the metabolism of a single glucose molecule is Two ATP molecules.
Answer:
Common examples of physical contaminants include hair, bandages, fingernails, jewelry, broken glass, metal, paint flakes, bone, the body parts of pests, or pest droppings.
Explanation:
For giving you understanding ; we need Free O2 but Oxygen is also available in H20 right why dont we use it !!
As the early atmosphere was reducing as there was no free oxygen but it was later produced by chemoautotrophic bacteria !! Living thing release O2 in atmosphere thus making it oxidising in nature and then life evolves !!