Which of the following must be true for diffusion to occur? Molecules or particles must have different sizes.

Special protein channels must always be available.

There must be areas of different concentrations.

Energy must be available.

a- all cells come from pre-existing cells

genetic variation can be caused by mutation (which can create entirely new alleles in a population), random mating, random fertilization, and recombination between homologous chromosomes during meiosis (which reshuffles alleles within an organism's offspring).

answeranovulation;