Which of these best describes the role of plants in the carbon-oxygen cycle? a. to absorb oxygen from the atmosphere and release carbon dioxide into the atmosphere b. to absorb carbon dioxide from the atmosphere and use it to make sugar c. to absorb oxygen from the soil and use it to make carbon dioxide for sugar production d. to absorb carbon dioxide from the atmosphere and release it back into the atmosphere

In this case, the statement that people who exercise for an hour may have lower cholesterol levels is .

Ais a group of individuals of the same that exist together in the same place at the same time

To answer this question, researchers studied populations of the dusky salamander (desmognathus ochrophaeus) living on different mountain ranges in the southern appalachian mountains. the researchers tested the reproductive isolation of pairs of salamander populations by leaving one male and one female together and later checking the females for the presence of sperm. four mating combinations were tested for each pair of populations (a and b)—two within the same population (female a with male a and female b with male b) and two between populations (female a with male b and female b with male a). the proportion of successful matings for each mating combination was measured. for example, when all the matings of a particular combination were successful, the researchers gave it a value of 1; when none of the matings were successful, they gave it a value of 0. then the researchers calculated an index of reproductive isolation that ranged from 0 (no isolation) to 2 (full isolation). the reproductive isolation value for two populations is the sum of the proportion of successful matings of each type within populations (aa + bb) minus the sum of the proportion of successful matings of each type between populations (ab + ba). the table provides data for the geographic distances and reproductive isolation values for 27 pairs of dusky salamander populations.