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Green leaves

Postby Bguerra » Thu Nov 17, 2005 11:02 am

The title of my project is DO leaves need sunlight to stay green?

I placed 8 different kinds of leaves in 8 plasitc pouches and exposed them to sunlight and then the other set of 8 leaves, I placed them in between construction paper in a dark location for 8 days. The leaves that were placed in the plastic turn brown first, but the ones in the construction paper are still green. I expected the one expose to light to stay green longer. Is it because of the plastic I'm stuck Hopefull some can explain way this happen.

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Postby Artshark » Thu Nov 17, 2005 1:15 pm

I see how the results contradict not only what you expected, but 'science', so to speak. Believe it or not, your project actually sought to imitate winter! This is because leaves change their color to a dark brown in fall by removing the chlorophyll in their chloroplasts, as their will no longer be sufficient day light in winter to make food. One question: were neither of the sample sets given light and water? Good luck!

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Postby bradleyshanrock-solberg » Tue Nov 22, 2005 9:24 am

Well, what happened here is that you ended up testing for the wrong variable.

In one case you sealed the leaves away from air, but exposed them to sunlight.

In the other case the leaves could "breathe" but were kept from sunlight.

In both cases, the leaves were "dead" already, in that they weren't attached to a living plant.

So what you discovered is that dead leaves are preserved better in the dark, with construction paper, than in plastic pouches, in sunlight.

Unfortunately it is hard to say which factor caused the result, because the two trials had too many things different about them. My guess would be that the sunlight dried out the leaves (no photosynthesis when the leaves are dead, just removal of moisture) where the dark leaves retained their water longer and that the construction paper and plastic didn't enter into it, but I'm just guessing based on general knowledge of how dead leaves behave in the real world. (leaves on top of a pile, exposed to the sun, dry out faster than leaves in the middle of the pile)

Without more careful testing it is impossible to say for sure what the cause is. What is certain is that both the question and the control of variables was flawed. To test the connection between sunlight and green leaves, you would need living plants.

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Postby Artshark » Tue Nov 22, 2005 6:47 pm

Thank you Bradley, I see what you mean. :)

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