What is wrong with this experiment?

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.

What is wrong with this experiment? Explain.

Answer 1

i agree with tj. you cant have a valid experiment when each plant is different. use the same plant for each color light. and if you really want to know what color light is best for plants, test each species of plant with all the colors of light and then see which color worked best for each kind.

Answer 2

Your experiment doesn't address the possible difference in growth rates between the four types of plants. Why don't you use the same kind of plant under each light? It removes one variable, and makes for more reliable results.

Answer 3

Too many variables - if you're testing to determine what wavelength of light affects the most growth, the types of light should be the only variables in the experiment.  The experiment you described above also introduces the variable of different types of plants (which , by definition, have different growth rates).  Even if they all grow "quickly," they grow at different rates and will effect the results of the experiment.

To fix it, use only one type of plant under each light.