some species of fungi protists and bacteria play a vital role in every biogeochemical cycle including the carbon and nitrogen cycles which best indetifies their common role​

the answer is true when observing or determining population size, a direct observation is use, in which each organism is counted in a population or in an area. one benefit of this measure is that you get the exact population count but it will take a long time to  determine  the  size  of a  population.