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ETD 34: A. Why would a plant have leaves with green tops + red bottoms? B. Why do tree become more colorful in the fall?
December 11, 2013 at 7:48am


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Jordan Johnson
December 11, 2013 at 6:16pm


A) Learned that some plants have evolved to have red bottoms to help with photosynthesis. Because the red light that comes through reflects off the red bottom and gives the plant a second chance to hit the chloroplasts.

B) Trees become less colorful (biologically) in the fall because they lose pigment and not able to photosynthesize, so they die and fall off the tree.


After the discussion with my dad I got a better understanding of why plants have red bottoms and white bottoms. This ETD has also made me think more about why things actually happen instead of just accepting it. 

Sophie Wulfing
December 11, 2013 at 10:36pm

light energy hits the leaf, random that it hits a chloroplast.  A normal leaf would be waste dby going through the leaf.  By having a red bottom, the red reflects the red light back up into the leaf, providing another pass to hit a chloroplast.  Seen in the Amazon where there's little light for ground plants.  Better color could be white which reflects all colors, which is why leaves tend to be lighter on their bottoms.  Leaves don't actually get more colorful in the fall, they get less colorful and therefore reflect more colors of light.  They absorb less and reflect more.  This is a result of less light in the fall (not as much energy).

Sophie- I do have a question as to why the only colors that a plant and use are green and blue, and why they can't use green. I did have to look up that the green pigment in plants is due to chlorophyll and the red is due to anthanocyanin, which is in strawberries and grapes, and that they use this color to block out potentially harmful rays of light from their seeds

Francisco Perez
December 16, 2013 at 7:00pm

Parent: Francisco had told me that plants evolve depending on where they are located. The plant that has a red bottom is like that because of evolution and the light it receives. It reflects red light on the bottom and green on the top. Also, he told me that trees do not become more colorful in the fall instead the decrease in sunlight causes less photosynthesis to take place which means they lose green pigment. 

Student- I taught my mom that a plant can have multiple colors because it allows it to absorb more light. In fact, a white bottom plant would be ideal for a plant because white reflects all colors which will cause an increase in light energy for the plant. Also, i taught her about why leaves change color in the fall. Because of the decreases in photosynthesis.

Sam Paige
December 22, 2013 at 1:44pm

Parent: Sam taught me that all of this has to do with how much light and how plants absorb light for photosynthesis. The reason they are green at the top and red at the bottom is because they absorb purple-blue and red light the best and reflect green light more. Sam used the analogy of a vending machine that will take dollars, quarters and pennies but not nickels of dimes; the machine(leaf) takes in some currencies(light frequencies) and gives back others. They have red bottoms because sometimes light does not hit a pigment and the red bottom means that it is reflecting red light thus any light the misses pigments is reflected back through and has another chance to be picked up by a pigment. Trees leaves change color in the fall because they receive less light from their environment and so they need to absorb as much light as they can and thus must change color to absorb green light as well.

Student: This topic was much easier to explain to my mom however there were still some tricky parts. Mainly it was the part of having to teach her how light works and I did that by using posters in my room explaining how we see a color from a poster because it is absorbing all other light and only reflecting that color light. Once this was out of the way it was easier and I was able to use an analogy about a cashier or vending machine only accepting certain types of currency to explain how plants absorb purplish-bluish and red light better. then I was able to explain that a red bottom was like a safety net which saves light that would be other wise lost. Then explaining about trees was a little more difficult because she wasn't getting the idea that the pigments act like the posters. However finally I was able to explain it to her and she got it fairly well. By figuring out how to teach my mom I understand the subject better especially because she has never been as she says "great at science" so I have to work harder to make the information really simple and then work her up to more complex understandings.

Kevin Turek
January 01, 2014 at 1:03pm

Parent: Kevin Told me that some plants have green on top and red on bottom to help them gain as much light as they can. They are actually every shade except the color they display because they reflect that light. With this the plant can take the green light and then if it misses some the red will reflect it back to the chloroplasts again. Also the leaves change color in the fall because they lose there chlorophyll.

Student: My mom found it interesting that plants actually reflect the only shade they are not. Also she just believed the leaves were too cold and died when they fell off there trees. This was easier to explain, simply because I think I'm getting better at these subjects.

Brett Babbel
January 05, 2014 at 8:55pm

Parent: I learned how plants have adapted the color of their leaves to help them absorb light energy to help the photosynthesize. I didn't realize all the many features plants have to help them extract as much rays of sunlight as possible. I learned that the color of the leaves dictates the type of light rays it absorbs for photosynthesis and that plants actually reflect green light. And how plants need red and indigo colored light to do photosynthesis and thats why you find red bottom leaves which reflect the red light back to the leaf giving it a second chance to absorb the light ray. Also learned that white bottom leaves reflect all of the light.

Student: I did more thinking on the colors of light needed for photosynthesis, red and indigo, which are the on both ends of the wave length spectrum, Blue being one of the shortest wave length and red being the longest wave length. I found it strange how photosynthesis needs the biggest and the smallest yet none of the light in between. 

Kayla Harbold
January 06, 2014 at 7:10pm


A) Kayla was actually very excited to teach me about the differing colors of plants and why the differ, specifically in the color of their bottoms. to start off she told me that plants are green NOT because they absorb green light but they absorb all colors EXCEPT green light therefor causing our eye to see the reflected green light. So with that fundamental down Kayla could then draw a diagram of how light passes into a chloroplast and is absorbed however some light passes though and is very absorbed. But if the plant has a different color bottom such as red, and red light that passes through will be reflected back up into the chlorophyll and the plant has a second chance to absorb that light! A very effective method for gaining more energy!! 

B) TRICK QUESTION! Plants become LESS colorful in the fall. This is because they loose their pigments because during the winter it is not energy-efficent so spend it's energy making leaves when you have minimal light to power photosynthesis. Therefore during the winter leaves fall off and photosynthesis is put off until spring time.


Teaching my mom about leaves and how they function was very fun. I realized that when teaching people you have to give them background knowledge about the subject matter. The hardest thing for me was learning to not assume that she knew everything that I was talking about and they I had to teach her some basic principals about photosynthesis before we began otherwise I ended up reteaching her the basic idea. For example, I had to establish the reason why leaves are even green in the first place to further expand on why a red bottom is efficient. And once again, draw pictures always helped my mom see things more clearly than just my words alone. 

Kelli Vetter
January 06, 2014 at 8:22pm

Parent: The sun gives off light energy which is absorbed by the plant. Sometimes, the light photons miss chloroplasts in the top of the leaf so the plant cannot undergo photosynthesis. Fortunately, plants have a an underside which can give the plant another chance to hit a chloroplast. A plant that has a white bottom is the best plant to undergo photosynthesis because the white color reflects all the colors. The plants change colors because the pigments in the plant are breaking down, so they are essentially reflecting more.

Student: Most plants reflect green light, giving the plant its color. I was still confused about why most plants reflect green light when green light gives off the most energy in visible light. I looked it up and found out that the chlorophylls in the plant are easily damaged by high energy. The high energy can also damage the plant itself which could kill the plant. It  makes sense why plants evolved to reflect green light because in the end it is survival of the fittest, and reflecting green light protects the plant.

Madison Boggan
December 05, 2014 at 7:53pm

Parent: After hearing Madison talk about these plants that have leaves that are green on top and red on bottom, I say you guys should take a field trip to the rainforest to find some! I understand now that having this feature benefits the plant. It gives them a 2nd chance in the form of light energy being able to either hit chloroplasts in the green part or reflecting back up after hitting the red and hitting a chloroplast in the green on the 2nd try. I also learned that fall leaves don't actually gain color, they lose color. They always had the red / orange / yellow tint and once the chlorophyll shuts down, the other colors show. I'm excited to see this in a new way next fall!

Student: It was interesting to teach my mom about this because she loves fall and is always very interested in the leaves. She was surprised by the fact that fall leaves actually lose color instead of gaining it. I said it was like hiding a pink piece of paper behind a blue one. If you remove the blue paper, the bright pink might make you think color was gained but actually it was there all along and color was actually lost in the form of the blue paper leaving. I agree that I should go to the rainforest in search of a plant there that has leaves with green on top and red on the bottom. It made me realize how awesome it is that they have a second chance as I explained it to my mom. 

Anne Sweeney
December 13, 2015 at 10:14am

Parent: So the chloroplasts in the green leaf absorb the sun’s rays and if the sun’s rays miss a chloroplast in the green leaf above they pass through to the bottom part of the leaf which is red and this will reflect the light back to hit the chloroplasts which starts photosynthesis.  In the fall leaves become more colorful because the chlorophyll breaks down and the other colors which were present are able to show their true colors.  

Student: I was excited to teach my mom about leaves, as gardening and plants is something she is interested in! Explaining the green/red plant was easier when I drew it out and had my reasoning down. I realized that my mom and I are both visual and hands on learners, so when I explain something to her I have to incorporate both for better understanding. It was new to me that the leaves don't change colors based on the 'typical change in season', but that when the chlorophyll inside of them breaks down, we see all the other pigments that were already present in the leaf.

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