it is flu season! the flu is caused by a virus. scientists continue to debate whether or not viruses are alive. if we consider the image of the flu virus seen here, we could say that a virus is not alive because

All living organisms are composed of a. only one cell. b. at least 100 cells. c. at least three cells. d. one or more cells.

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.

This rapid change in species that rarely leaves behind fossil evidence is referred to as