After a certain drug is injected into a patient, the concentration c of the drug in the bloodstream is monitored. At time t ≥ 0 (in minutes since the injection), the concentration (in mg/L) is given by

c(t) =(40t)/(t^2 + 2)

What eventually happens to the concentration of drug in the bloodstream? ...?

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.

not sure if this is what you'r looking for prokaryotes have organelles hope this out at least.