The speed of a nerve signal is fastest in the

alpha motor neuron in the spinal cord

Explanation:

268 Speed (in miles per hour)  the fastest such transmission in the human body.

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.