Final answer:
In scientific experiments, variables can affect the outcome and must be carefully controlled. The pot size and soil type are likely independent variables in a plant growth experiment, with plant growth being the dependent variable. For a valid experiment, each variable except the one being tested should be held constant as a control.
Step-by-step explanation:
Understanding Variables in Scientific Experiments
In scientific experiments, identifying and controlling variables is crucial. A variable is an element, feature, or factor that can be changed and might affect the outcome of an experiment, while a control is a constant and unchanging standard of comparison in scientific experimentation. Based on the information provided, if you are setting up an experiment to determine how different factors affect the growth of plants, the size of the pot (a) and the kind of potting soil (b) you mentioned could be considered independent variables. The dependent variable could be the growth of the plants, which you are measuring. Essential controls might include consistent watering, equal amounts of sunlight, and maintaining the same type of environment for each plant.
In Gary's experiment, it's suggested that the container size for all plants should be the same to ensure it does not affect the growth of the plants, making it a control variable. Similarly, the requirement of giving all plants the same amount of water every day would serve to control for water as a variable, focusing the experiment on the effects of the independent variable, which might be sunshine in Gary’s hypothesis. Errors in experimental design, like varying additional factors such as soil temperature, can lead to confusing results and are referred to as experimental errors. In the example provided, where pots with and without detergent were used and placed in different lighting conditions, this represents a flawed experiment because it includes two independent variables when only one should be tested at a time.