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Does the amount or intensity of light affect a plant's phenotype?
Question Date: 2013-04-07
Answer 1:

Another student asked me a similar question recently about the color of light. Maybe you are in the same class. As you know, the phenotype is what the plant is like. For example, is it tall, does it have a lot of leaves, what is its shape, and what color is it? More intense light—which is another way of saying more light—provides more energy for photosynthesis. More photosynthesis means more building of molecules that the plant is made of—more growth and a bigger plant. Of course, there’s a limit where too much light is a problem high-energy light can actually damage the chlorophyll, which is the pigment that plants use to do photosynthesis.

Another problem is that with light, you get heat. This usually means that the plant will dry out too fast. To protect itself from drying out, the leaves will close their tiny holes (stomata or stomates). Unfortunately, this also means that they can’t get rid of the oxygen that they produce as a waste in photosynthesis. They also can’t bring in the carbon dioxide that they need for doing photosynthesis.

Can you just water the plant more? That will help if the light isn’t too intense.

Photosynthesis only works because there are many enzymes that speed up all of the chemical reactions. If the temperature gets too high, these enzymes can be destroyed. Then the plant will probably die.

You can test your ideas about plants for yourself by putting plants at different distances from a light source. According to the inverse-square law, the plants that are 10 cm away from the bulb will get four times the energy of the plants 20 cm away. Put soil in small cups and put 2 or 3 seeds in each. Be sure to design a good experiment. Have at least a few cups at each distance. Make sure that the cups are alike in every other way (don’t have some closer to the heater or the window, for example). Make careful measurements and write everything down.

If you are interested in questions like these, you may be interested in a career in botany or plant ecology.

Thanks for asking,

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