Final answer:
The independent variable in Sara's experiment is the amount of water given to the bean plants. For the experiment with detergent in the soil, the major flaw is that it contains two independent variables, which are the presence of detergent and the amount of sunlight, making it difficult to determine the effect of either factor on plant growth.
Step-by-step explanation:
The independent variable is the factor that is changed or controlled in a scientific experiment to test the effects on the dependent variable. The dependent variable is the factor that is measured or observed to see how it is affected by the independent variable.
In Sara's experiment, the independent variable is the amount of water given to the bean plants because this is the
factor that Sara is changing. One plant receives 15ml of water each day, and the other plant receives 10ml of water each day. The dependent variable would most likely be the growth of the bean plants, which Sara would measure to see how it correlates with the different amounts of water provided.
Regarding the experiment with the presence of detergent, the mistake is that there are two independent variables: the presence of detergent in the soil and the differing sunlight conditions (sun for the detergent pots, shade for the non-detergent pots). The experiment should have only one independent variable to accurately measure its impact on plant growth. Other factors, such as soil temperature, evaporation, insect effects, and individual plant variation, should be controlled to ensure that they do not influence the outcome of the experiment.