Matter is recycled within and between ecosystems through closed loops called biogeochemical cycles. How is this unlike how energy is passed through ecosystems? A. Energy has a multidirectional flow.
B. Energy is constantly reused.
C. Energy has a one-way flow.

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.