Final answer:
To determine how different liquids affect plant growth, the controlled variables should mainly include the plant type, soil amount, sunlight exposure, and pot type. Uncontrolled factors in a similar experimental setup may consist of individual plant variation, soil temperature differences, evaporation rates, and potential insect effects.
Step-by-step explanation:
In an experiment designed to see how different liquids affect plant growth, several variables should be kept constant to ensure that the results are due to the independent variable (type of liquid) alone. These controlled variables include the type of plant, the amount of soil, the amount of sunlight, and the type of flowerpot. Keeping these factors constant ensures that the plants are growing under as similar conditions as possible, except for the liquid they are receiving.
Regarding Gary's experiment, the variables that he may not have controlled could potentially influence his results. These include individual plant variation, soil temperature caused by different colors of containers, water loss due to evaporation from the soil, and the effect of insects which may attack one set of plants but not the other.