What is wrong with this experiment? Explain.?

Question

Consider the following experiment procedure.

Question: Which color light is best for plants?

Hypothesis: If plants are placed under red light, then they should grow faster and better.

Set up: There are four plants: Green Bean, butter bean, rye grass and a sunflower. These plants grow rather quickly. The green bean plant is placed under white light and is used as the control. The butter bean is placed under green light, the rye grass plant under red light and the sunflower under blue light. All the plants are watered one cup of water ever other day and kept under the light the same amount of time. At the end of 4 weeks, the sunflower plant grows the most.

Answer 1

They should have exposed different specimens of each plant to each color of light.  The test results don't answer the question very well, because there are many possible reasons for the sunflower plant growing the most.

i.e.

1.  Blue light helps plants grow better.

2.  Blue light helps sunflowers grow better.

3.  Sunflowers grow better than the other plants under these conditions, regardless of the color of light.

And others.  A better experiment would be to test four different sunflowers under four different colors of light, and see which one grows the most.  Then repeat for green bean, butter bean, and rye grass.  And see if one color consistently performs better.