Students collected the above items to test the effects of different factors on indoor plant growth. These items include potted plants, water, plant food, and a lamp to provide light. Which procedure will best determine if more food makes plants grow taller?

Question

A.
Water both plants the same amount each day.
Expose both plants to the same amount of light each day.
Give one plant the larger plant food packet, and give the other plant the smaller one.
Measure both plants' heights after one month.
B.
Divide all of the plant food evenly between both plants.
Water both plants the same amount each day.
Expose both plants to the same amount of light each day.
Measure both plants' heights after one month.
C.
Water both plants the same amount each day.
Expose both plants to the same amount of light each day.
Split the larger plant food packet evenly between both plants.
Measure both plants' heights after one month.
D.
Give one plant the larger plant food packet, and give the other plant the smaller one.
Water one plant, but not the other.
Expose both plants to the same amount of light each day.
Measure both plants' heights after one month.
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Answer 1

The best procedure to determine if more food makes plants grow taller would be A. Give one plant the larger plant food packet, and give the other plant the smaller one. Measure both plants' heights after one month. This procedure isolates the effect of the different amounts of plant food on the plants' growth, as the water and light conditions are kept constant for both plants.