Like animals, plants undergo cellular respiration to produce energy. plants use oxygen and release carbon dioxide and water. water returns to the atmosphere and becomes part of the water cycle through the process of a) condensation. b) perspiration. c) precipitation. d) transpiration.

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.