Lichens are a mix of two organisms—a fungus and an alga. the alga, by virtue of its ability to carry out photosynthesis, provides food for the fungus. the fungus, in turn, protects the alga by forming a covering over it. what kind of an interaction is being exhibited by the fungus and the alga?

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.