It’s c cause I know and I was just too lazy to type the word lol
Even if a microorganism is a part of the normal microbiota of a human being, it may cause the death of the person. For example, say E. coli, it resides in intestines and is harmful. But, if its number increases way too large, it may cause infection (Colitis) and even death. So, even the normal microflora needs to be present in the controlled quantities, inside the body.
Scientists believe that the Earth's early atmosphere lacked oxygen because photosynthetic organisms did not yet exist. Hope this helps and have a great day!
Active transport. this is the only transfer of material that is again the concentration gradient, unlike diffusion or osmosis
