Science Buddies: "Ask an Expert"

My 3rd grade son has been conducting his science project for the past 2-3 weeks on the effects of red, yellow, and blue light on how plants grow. Essentially, I have been noticing that they have been growing at a similar pace. However, this weekend, evidentally, my son forget to water the plants and they pretty much died. I am currently trying to start the project over, but with a week to go, I do not know what the final results should be. Does anyone know what the results are supposed to be? The sight where we got the project from did not have the results posted. I have heard that the blue light was supposed to be the best, but I could not confirm.

Howard

Hi howard,

Normally this kind of experiment is done with varying levels of intensity of white light. Is your son really studying phototropism (how plants move towards light), or is he just seeing how healthy the plants will be with different colors of light?

If you are doing different colors, what you are really measuring is what wavelength of light is the best for photosynthesis. Some of the colored light will be better at growing healthier plants. I suppose you can also measure how effective the wavelength is in attracting the plant (i.e. having it move towards the light), but like I said, this is normally done with varying levels of intensity of one color of light.

Don't worry, your son's experiment is not a failure. If the plants don't grow quick enough to get results, just have him explain the mistakes he made and have him write in his report what he expected the results to be and why, and how he could improve his experiment in the future. The most important part of this project is that he followed the steps of the scientific method and learned how plants use light to make their own food.

You might try radish seeds, as they are supposed to grow pretty quickly, but I don't know how much they'd grow in a week, probably not much. If you really want your son to have a project with results, we have a list of projects that only take a day to complete and require readily available materials:
https://www.sciencebuddies.org/science- ... arents.php

The answer to your question about which wavelength is best is on this page: http://www.sunmastergrowlamps.com/SunmL ... lants.html

We actually just wrote a blog entry about experiments that don't turn out the way you expect: https://www.sciencebuddies.org/blog/201 ... cience.php

I would help him understand the difference between absorption and reflection of different colors of light, and why plants don't use green light.

We have some project ideas about this topic which might be useful to you:
https://www.sciencebuddies.org/science- ... p015.shtml
https://www.sciencebuddies.org/science- ... p041.shtml

And, check out our project guide too, which will guide your son through writing up his report and doing a display board:
https://www.sciencebuddies.org/science- ... ndex.shtml

Also, I can't tell from just one post how involved you are with the project, but I want to remind you to let him do as much of the project as he can. Parents have a habit of helping too much sometimes .

Good luck and let us know if you have more questions!