Final answer:
The question asking if water affects grass growth is indeed testable by varying water amounts and measuring growth. The main variable in Gary's experiment is water, and such an experiment would involve controlled conditions to isolate the effects of different factors on plant growth.
Step-by-step explanation:
A student wants to know if the amount of water grass receives affects the growth and whether this is a testable question. Yes, this is a testable question because it involves a manipulation of a variable, which is the amount of water, to observe an effect on another variable, the growth of grass. To test this, you could set up an experiment where grass is given different quantities of water over a period of time, and the growth is measured and recorded.
Considering Gary's experiment, the variable being tested in his experiment is the effect of water rate on plant growth. However, if he wanted to solely focus on water as a variable, he would need to make sure all other conditions like sunlight, soil type, and any other additives are kept constant across the plants being tested.
In regard to a lab experiment studying plant growth, it would involve controlled conditions where variables such as amount of sunshine, type of soil, and water are manipulated one at a time to see their individual effects on plant growth. For proper scientific validity, all other factors must be kept constant, and only the one variable being tested should change.