Decomposers are essential in breaking down organic matter into useful ones. For the nitrogen cycle, they break down bodies of dead organisms turning it into ammonia. Also, some bacteria break down nitrates turning into nitrogen which goes back to air.
Fungus because it is a living thing in its own right as opposd to a brain cell which is part of an organism.
Monoploid organisms reproduce asexually since they need to transmit all of their genetic material to their offspring. Diploid organisms, have 2 copies of their genetic material that differ slightly in their genes. Since the progeny gets half of the DNA from each parent, we have that new combinations can emerge; for example, if the mother is AA for some allele and the father aa, their offspring will be Aa, a new genotype. This might have different implications (for example, the recessive gene for thalassemia also provides resistance to malaria). Finally, during meiosis, there is also an event called crossover that increases the genetic variation of the offspring.
