Scientists tested the effect of a fertilizer on the growth of plants. they had 2 sets of plants, group a which gets fertilizer, water and sun and group b which gets only water and sun (but in equal amounts to group a).
1. explain how this scenario is a controlled experiment and identify the manipulated variable.

2. if the scientists only performed 1 experiment but it supported their hypothesis, why can it not be considered a theory?

3. the graph below was created showing the growth of the plant. how would you know that the y-axis is measuring the growth of the plant?

Would really appreciate it, i have an idea but not completely sure

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.

How can a geological time scale best be reconstructed? a) comparing vestigial structures in living species b) comparing homologous structures in living species c) examining homologous structures in fossil remains d) examining the written records of scientists from past cultures