In biology, factors that limit a population are known as density limiting factors. These factors are classified into density-dependent if they affect populations with a high density such as predation or food availability or as independent if they affect different populations of animals despite their density which includes mainly disasters such as fires or floods.
This means the forest fire described is a density-independent factor because the population of birds and trees were reduced or limited but this did not occur because of the density of the population as all species in the forest are affected no matter if the population if high or low.
A. Bacteria are single-celled. I think it would be this because humans have way more than one cell, and the other ones are the same as us. Just guessing
