In kidney cells, charged ions like sodium and chloride are reabsorbed from the urine against a concentration gradient. which mode of cellular transport is employed here?

select one of the options below as your

a. facilitated diffusion
b. simple diffusion
c. osmosis
d. active transport

Which of the following statements is true about the relationship between genetic variation and natural selection? a. genetic variation must be present in a population before natural selection can act on it. b. genetic variation arises in a population as a result of natural selection. c. natural selection can act on a population whether there is genetic variation within the population or not. d. after natural selection acts on a population, the amount of genetic variation in the population always increases.