To determine the effect of color of light on plant growth, 4 groups of bean plants were grown under the light conditions below.
group 1—under red light group 2—under green light
group 3—under violet light group 4—in normal, white light
which of the variables below should be held constant?
options:
the color of light each group of plants receives
all of the above
how much each plant grows
the amount of light each group of plants receives