A biologist is using a dichotomous key to identify fish. 1. (a) Has a single dorsal fin ® 5 (b) Has a double dorsal fin ® 2 2. (a) One fin is spiny, the other is smooth ® 3 (b) One fin is not spiny or smooth ® 4 5. (a) Has small fin on back near tail ® 6 (b) Has no fin on back near tail ® 7 6. (a) Has barbs near the mouth ® Catfish (b) Does not have barbs near the mouth ® 10 7. (a) Tail is asymmetrical ® 8 (b) Tail is symmetrical ® 9 10. (a) Scales are small ® Trout (b) Scales are large ® Whitefish What is the next step to take to identify a fish that has a single dorsal fin and no fin on the back near the tail? step 5 step 2 step 7 step 6 Mark this and return

What is called the "building block" of life?

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.

Knowing the importance of the essential elements, why would someone chose a diet that does not address all of them?