Which telescope gathers only visible light

How many pounds does the earth weigh?

What determines whether a particular cell is able to respond to a hormone?

What is a population? a. all the members of the same species living in the same ecosystem at the same time b. the number of a species living in the same ecosystem over a period of time c. the total number of organisms living in an ecosystem at a point in time d. all the members of a food web in the same ecosystem