Independent variable in a investigation is the factor you control and change (e.g. in plant biology it could be light intensity, a concentration level of substances in added water or soil) that influence the dependent variable (in plant biology this would be the rate of photosynthesis). There must be a number of groups to prove the influence of the independent variable on the dependent variable and trials to increase credibility of the results. Remember to include a control group where independent variable is not changed. (e.g. in measurement of light intensity on the rate of photosynthesis there must be a control where the light intensity is not manipulated to present the regular rate).
