Effects of colored light on leaves

Danielle · Post by **Danielle** » Sat Mar 31, 2007 3:54 pm

I have put different colored transparencies (red, blue, green, yellow, clear, and black construction paper) onto leaves of 2 philodendrons. The transparencies have been on the plants for a week and i don't notice any change in color of the leaf. What is supposed to happen to the leaves?

MelissaB · Post by **MelissaB** » Sat Mar 31, 2007 4:53 pm

Danielle,

What grade are you in? Have you looked up the term 'photosynthesis' on Google or Wikipedia.org? That may help you to understand what should happen in the experiment (note that frequently in science, what is 'supposed' to happen doesn't necessarily happen--and that's okay!).

Do you see any changes in your plants with black construction paper? And are the covers on all the leaves on the plants, or just some of them? It may be that not enough time has passed to see an effect...

Danielle · Post by **Danielle** » Sat Mar 31, 2007 4:58 pm

Im in seventh grade and i did look up the term. but nothing has happened at all with the black construction paper and i thought that the leaf would turn yellow due to lack of light but nothing has happened. Nothing has happened to any of the other leaves with the other colors either and the plants are by a sunny window. Is it possible that it would take more than a week for the leaves to change in any way?

deleted-2131 · Post by **deleted-2131** » Sat Mar 31, 2007 8:21 pm

Danielle,

The plant's leaves may only be affected if the ENTIRE plant is covered. (e.g. an entire plant covered in black paper, an entire plant covered with yellow transparency, etc.) If you are only covering part of your plants, then that would explain your results.

In addition, it's important to remember that photosynthesis is a series of chemical reactions dependent on the wavelength of light striking the chloroplast. It is entirely possible that just becaue the transparenies are different colors that they are not filters changing the wavelength of the light passing through them.

If you need more help understanding this, please ask!

Danielle · Post by **Danielle** » Sun Apr 01, 2007 5:11 am

Terik,

I got this experiment from the Science Buddies website...

https://www.sciencebuddies.org/mentorin ... ?from=Home (Leaves and light)

It told me only to buy one plant and "space the different colored sleeves out upon the plant." It said that after one week I should remove the sleeves and note the appearance of the leaves.

I am already one and a half weeks into this project and cannot change my idea because the teacher has already approved different steps in the project in my logbook. What should I do?

deleted-71588 · Post by **deleted-71588** » Sun Apr 01, 2007 7:18 am

My experience with philodendrons is that they are VERY tolerant to a wide variety of lighting conditions and neglect (I tend to kill plants that are intolerant of drought and lack of attention). Their vine like nature means they share nutrients, energy, etc over long distances along a shoot or run.

I'm just guessing here, but you might get a bigger effect if you treated all the leaves on a run identically. That should cause the same effect on all leaves on the run and reduce their ability to compensate. If the filter on that run was detrimental, it should show up sooner.

Now lets talk about light and filters. Even the best scientific grade filters aren't perfect, they only block some percentage of the light energy at each wavelength (or frequency). If you have a strong enough light source in a wavelength that the filter is supposed to block, it will only blocks a percentage, so you still get energy in that wavelength through.

If you have enough light in the correct wavelengths and filters that don't block a high enough percentage and are using a plant that doesn't need much light to begin with, then the differences are probably going to be very small.

Do you have a room that you can temporarily keep dark most of the time? By reducing the length of time the plant has light and the strength of the light, you MAY be able to induce a difference caused by your filters if you combine this with the idea of filtering a whole run with the same filter.

MelissaB · Post by **MelissaB** » Sun Apr 01, 2007 7:37 am

I think Craig's right about all of this. So, as for what to do now, you have two options. I don't know what sort of approval you may need from your teacher, so I don't know which one you can do.

1. Change your methods. Like Craig said, it would be good to reduce the plant's exposure to light and/or to filter all the leaves on one part of the plant. Could you do a second follow-up experiment where you bought multiple plants (one for each color filter) and covered all their leaves?

2. Do nothing! You did an experiment, and it didn't work the way you expected. As I said in my very first post, that happens a lot in science. Famously, we wouldn't have penicillin if not for a scientific 'accident' where the experiment didn't work! It's fine to not have the results you expected to get--especially if you can explain them. Craig has given you several hypotheses for why you didn't see a difference--the filters didn't work properly, or the philodendron is sharing nutrients amongst its leaves. Alternatively, perhaps not enough time has passed to see a difference.

Danielle · Post by **Danielle** » Sun Apr 01, 2007 8:42 am

Thanks for your help. I will try your suggestions and see what works.

deleted-71588 · Post by **deleted-71588** » Sun Apr 01, 2007 10:03 am

Now that Melissa has taken us from thinking about the issues to actually thinking about modifying the experiment... You need to think about scientific methods again!

Your original experiment was basically using different portions of the same plant as a "self-control" (even though you had two plants, presumably that was just to prevent a single accident from wiping out your experiment). The only real control concern was that the plant was rotated so that the amount of light reaching each part of the plant was roughly the same.

If you start treating different whole plants differently, you loose the "self-control" aspect and you need a LOT more plants in each group plus an equal number in a control group to keep a scientific basis. This would be a MAJOR change in methods and if I were your teacher, I would frown on it! Having room for enough plants might be a problem for your parents.

Changing methods in mid stream with the same plants is also BAD! Again, you are introducing change to something that already has a different history. You need to continue treating your existing plants and leaves the same way and see what happens. If I were your teacher, I would frown on you not continuing the original experiment with the proposed methodology with the existing plants!

Any reasonable science teacher should welcome you going further with a second independent experiment that might explain why you aren't seeing much of a difference in your original experiment. This takes a new set of plants and a new altered proceedure with thought out controls. You really don't need your teacher's approval to do another experiment entirely on your own. What you do need is your parent's approval. You will need your teacher's approval to use the results of any new experiment for a graded project, so it wouldn't hurt to talk about doing a second experiment before you start!

Danielle · Post by **Danielle** » Mon Apr 09, 2007 12:35 pm

Unfortunately, I did not read your post after I posted my last reply. Not realizing that changing the experiment on the existing plant was BAD, I went ahead and put all the sleeves of the same color on one run of the plant. For the past week, all the runs have the same color transparency on them. Still nothing has happened. I have not been able to get the advice of my teacher because we are on spring break and the experiment is due in one week.

I was assuming that the leaves covered in blue and red transparency would stay green because blue and red light is absorbed by leaves. I was assuming that the leaves covered in green would suffer because green is reflected and not absorbed. The same effect wold happen with those covered with yellow. I thought that the clear transparency leaves would be okay because they were receiving all light and the black construction paper would die from lack of sunlight. The green and yellow covered leaves are still green and so are the black construction papered ones. With one week left, I must now prepare my display and I guess I must now state that my project did not work and that is part of science. I really wish my assumptions had been correct and would have worked.

deleted-71588 · Post by **deleted-71588** » Wed Apr 11, 2007 9:31 am

Given your experimental results (no visible change on any leaves) your mid experimental change in methods didn't create a lot of unanswerable questions.

You still have the what would happen if you ran the experiment longer and/or with lesser amounts of light, but that is about where you were a week ago.