Experiment with Light Color - Knowledgebase Question

Goshen, NY
Question by zahra7
December 13, 1997
I'm doing this experiment with 4 different types of plants: Jade, Ivy, African Violet, and a Birdsnest Fern. I'm testing how different colors of light affect their rate of transpiration. I'm unsure of how to water them. Should I water them every other day with the same amount of water?

Answer from NGA
December 13, 1997


This is a difficult question for me to answer, and it seems like a very complex experiment. How are you measuring the rates of transpiration? With four different types of plants, and several different light levels, you must have lots of plants! (I assumethat you have more than one plant for each treatment--usually a scientist has at least 2, but preferably more, plants getting each kind of treatment so the results don't depend on just one plant.)

If you trying to compare the transpiration rates of the different types of plants (ivy vs. jade with green light, for ex.), then you would have to give them all the same amount of water, to make sure that light color is the only variable.

If you are comparing transpiration rates for each typeof plant (ivy with blue light vs. ivy with green) then you should give each type of plant (all the ivies, for ex.) the same amount of water.

If you water a jade plant with the same amount and frequency of water as you do a fern or ivy, the plant probably won't last long--it will be getting too much water. If you are doing the second type of experiment I describe above, you might water all the jade plants with one half a cup of water once a week; all the ivies with one half a cup twice a week, or whatever seems best for the conditions (The amount of water the plants need depends on light level, pot size, humidity, etc.) You won't be able to get any meaningful result comparing the transpiration rates of different types of plants this way, however.

Next time, when you are designing an experiment, I suggest you keep it simple. Instead of trying to experiment with many different types of plants, choose one or two and have several "reps", or repetitions, of each treatment. For example, grow 16 pots of ivy. Place four pots under blue lights, four under red, four under green, and four under white (full spectrum). Then average out the data from the 4 reps, and compare the four treatments. Also, when designing an experiment, you needto think of all the possible variables--like watering--and incorporate those into the design so that you are testing only one variable. You could even design an experiment that investigates if the amount of water a plant receives affects its rate of transpiration! I hope this is helpful, and good luck!

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