What is a population?

all the organisms in an ecosystem
a collection of all the abiotic factors in an ecosystem
a collection of all the biotic factors in an ecosystem
a group of organisms of the same kind or species

Molecules like glucose and amino acids are not lipid soluble, so cannot cross the cell membrane by simple diffusion. instead, they are shuttled across by carrier proteins in the membrane from high to low concentration. does this process require energy from the cell? this is an example of what type of molecular movement?