placebos are used in experiments to group of answer choices control for the variability of individuals who tend to volunteer for research studies. control for the expectations of some research participants that they will improve just because they are in a research study. determine whether an independent variable actually causes a statistically significant change in a dependent variable. make certain that the treatment and control group are randomly selected.

If a fungus a plant take up water and nutrients, that would be an example of which type of relationship? a. commensalism b. symbiotic mutualism c. predation d. parasitism

The earth consists of a variety of different organisms. despite their diversity, however, some similarities on the structural and metabolic levels may be seen. these similarities can be attributed to a. similarities among organisms in their proteins and nucleic acids. b. the ability of organisms to readily adapt to sudden environmental changes. c. similarities in organisms' habitats and niches. d. the ability of all organisms to interbreed and produce new species.

Which of the following describes a boom period? a. as one population increases, another population decreases. b. as one population increases, the other population also increases. c. as one population decreases, another population increases. d. as one population decreases, another population also decreases