How does climate affect the rate of weathering

Which macromolecule catalyzes chemical reactions this be considered enzyme chemical reactions thus he considering enzymes

Stephen is a student who wants to test his knowledge of medical terminology. which option could he use?

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.