Agroup of scientists are studying the effects of different fertilizers on the growth of pea plants. they began their study with 10 pea plants. they gave each plant a different type of fertilizer and tracked their growth over a period of 2 months. the results of this experiment weren’t considered valid by other scientists because there was no control group. which of the following represents an appropriate control group for this experiment? a. a group of plants that’s not subjected to any fertilizer b. a group of plants that’s subjected to one fertilizer c. a group of plants that’s subjected to all types of fertilizers d. a group of plants that’s subjected to two fertilizers

1. the is the thinnest part of the earth. 2. the is the thickest part of the earth. 3. what metals are mentioned in the text?

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.

Cathy hypothesized that corn would not grow in mud. to test this hypothesis, she took corn kernels and placed 5 in mud, 3 in soil, and 2 in water. to her surprise, the kernels in the mud grew faster than the kernels in the soil. what error might have caused these unexpected results? a. wrong hypothesis b. not enough variables c. undefined control d. too many variables