Question

a scientist wants to test the effect of water temperature on the success of developing frog embryos. the scientist monitors developing embryos in different water temperatures and counts the number of embryos that mature into tadpoles. why should the scientist keep all variables except water temperature constant? to protect the developing embryos to ensure that the results only reflect changing temperature to test multiple variables at once to ensure at least some embryos develop into tadpoles

Explanation:

In a scientific experiment, to accurately determine the effect of the independent variable (water temperature in this case), other variables must be controlled. This is to avoid confounding factors. If other variables are not constant, it would be impossible to know if the result (number of embryos maturing into tadpoles) is due to water temperature or some other variable. For example, if water quality (another variable) also changed, the result could be due to water quality instead of temperature.

Answer:

to ensure that the results only reflect changing temperature