A student places four identical cells into four different liquids. Cell Description of Liquid
W Saltier than the cell
X Less salty than the cell
Y Higher concentration of water than the cell
Z Lower concentration of water than the cell
Which cells would take in water and swell?
cells X and Z
cells W and Y
cells X and Y
cells W and Z

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.