Why are plants green?

Factual Questions
1

I just found this site and it looks interesting. Is this site worth investing some time to get to know? I’ve spent some time on other boards and many seem to be dominated by a few who talk amongst themselevs and ignore newcomers but this site seems to have a different feel to it. It also seems to have many science topics, which I like but don’t get to spend much time thinking about these days.

I have a question that I’ve wondered about from time to time. Our sun is ‘yellow’ but plant life is green. Wouldn’t it be more efficient for plant life to be yellow so as to absorb sunlight better? Wouldn’t our plants do better under a green sun?

Stupid question?

If so, I apologize.

2

Clorrophyl is green. It’s what plants use to synthesize sunlight into food.

Zev Steinhardt

3

Same question then except substitute Chlorophyll for plant.

4

Or maybe a better question would be, why do plants use chlorophyll and haven’t evolved a mechanism for taking better advantage of the ‘yellow’ sun. Maybe there is no better?

5

Plants are green because of chlorophyll.

Objects that are color X, appear to be that color because that is the spectrum of light they reflect. Thus, if plants were yellow, they’d reflect most of the sun’s light in that part of the visible spectrum.

White vegetable matter (like mushrooms) doesn’t have chlorophyll, and they appear white because they reflect nearly the full visible spectrum back at us.

6

It’s green because plants (specifically, cholorphyll) reflect green light.

One thing you can be sure of, if something’s yellow, it’s not absorbing much yellow light.

The sun’s light is pretty close to white, anyway.

7

Here’s a question, then: Why are wavelengths in the “green” area of visible light so comparatively useless to plants? What makes them less valuable for photosynthesis than other wavelengths?

And welcome to the SDMB, Hippydippy.

8

Oh! So plants using cholorphyll would to really crappy under a green sun?

Thanks for the welcome toadspittle.

9

to=do

10

Exactly. Most of the light absorbed by chlorophyll is in the upper-end blue-violet range of the spectrum, and the lower red range as well.

Here is a bit of a primer on how chlorophyll works.

And another “welcome to the boards!”

11

Thanks for the link, Finch.

So, Terran plants using cholorphyll would not do as well if we were to put them on an Earthlike planet around a Green sun but looks like it would do well with a more ‘violet’ sun? Or is the ‘color’ of the sun irrelevant to the wavelength of light it emits?

12

Here is a very good primer on chlorophyll and photoreactive pigments in general.

http://www.ucmp.berkeley.edu/glossary/gloss3/pigments.html

It still does address the question of why but is very good base info.

The why can or cannot be answered in a couple of ways.

  1. We didn’t design it, so we can’t answer.
  2. God must like green.
  3. With enough research, we may be able to say that there isn’t any reasonable alternative.
  4. If we find alternatives, we might simply assume that nature hasn’t found them yet.
  5. or the alternatives might be difficult enough to make that it isn’t worth effort for the increase in efficiency from it.

Some of the necessity of different chlorophyll types has been gotten around by the use of accessory pigments as stated in the linked document.

Hope the enumerated answers don’t seem flippant, but that seems to be the ways of looking at that I can identify.

13

ooops: It still doesn’t address…

14

Here is yet another site, which actually looks pretty in-depth. Specifically, look around pages 3-5. The blue end of the spectrum appears to be used primarily because of the energy content of each photon; this energy drives the various reactions involved in photosynthesis.

15

The theory is that plants evolved from green algae that competed with purple algae which already used the profitable green part of the light. They eventually outcompeted them and are now kinda stuck with being green, for some reason. Here’s a thread with some more info: Why aren’t plants black?

(I don’t think there can be a green sun. It’s a glowing hot ball of gas, the color of its light is mainly determined by its temperature. With increasing temperature the visible color of thermal radiation ranges from dark-reddish, over yellow, white, to whitish-blue.)