Naked Science Forum
General Science => General Science => Topic started by: chris on 27/06/2006 22:08:37
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I have just received an email from Dirk at Stanford in the US.
His question really intrigued me because I can't answer it. Maybe someone here can help me?
Here it is:
"I have a simple question that's been bothering me for a while. Why are most plants green? Sure, it's because chlophyll rejects green, but why does it?
The green part of the solar spectrum is the most intense. It seems like a waste to reject it."
Chris
"I never forget a face, but in your case I'll make an exception"
- Groucho Marx
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That's an easy 1.
Cytochrome molecules are present in all living organisms and chlorophyll molecules are their kissing cousins. That means it wasn't a particularly large evolutionary leap to produce chlorophyll. Plus, of course, plants were originally aquatic, and green light doesn't penetrate water particularly well.
Chlorophyll is pretty good at absorbing red light and as plants do not even absorb all of the blue & red light they get, what's the point of being able to absorb yet more energetic light?
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Thanks Eth.
I'm not sure I agree with your point about water. Red is strongly absorbed / scattered by water, blues and greens much less-so. That's why blood from cuts (or even shark attacks) looks a bizarre dark colour underwater. So ideally, by your argument, aquatic plants should absorb green and reject red wavelengths.
Chris
"I never forget a face, but in your case I'll make an exception"
- Groucho Marx
-
Maybe plants just don't like red
Brand new forum at
http://beaverlandforum.y4a.net
More than just science
-
quote:
Originally posted by chris
Thanks Eth.
I'm not sure I agree with your point about water. Red is strongly absorbed / scattered by water, blues and greens much less-so. That's why blood from cuts (or even shark attacks) looks a bizarre dark colour underwater. So ideally, by your argument, aquatic plants should absorb green and reject red wavelengths.
Chris
"I never forget a face, but in your case I'll make an exception"
- Groucho Marx
Just thinking on the hoof, so to speak.
Photosynthesis needs light, but it also requires CO2, and requires to be able to dispose of O2.
Could it be that in the depths of the oceans, there is either a deficit of CO2, or a risk of too high a buildup of O2; and so it makes sense to switch off photosynthesis as one gets deeper.
Another issue to consider is how many hours of the day is the light available. Blue/green peeks around midday, but reds are available far further into the extremities of the day, the dawn and the dusk.
George
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Seaweed of course uses a different reddey version of chlorphyl, which must mean that it absorbs the blues and greens which travel through water the best, which makes sense.
All the green sea plants are based quite shallow, so I suppose that green chlorophyl must have some advantage if you get the whole spectrum, but I don't know what.
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quote:
Originally posted by daveshorts
Seaweed of course uses a different reddey version of chlorphyl, which must mean that it absorbs the blues and greens which travel through water the best, which makes sense.
All the green sea plants are based quite shallow, so I suppose that green chlorophyl must have some advantage if you get the whole spectrum, but I don't know what.
I think both of my suggestions could apply to this.
That green plants tend to grow near the surface would indicate they know where the surface is, and if the use the colour of light to tell them when they are near the surface, then this would certainly be one way of doing it.
Beyond that, as I suggested, maybe the number of hours of daylight in each spectrum might make a difference. If this is the case, then it should imply that plants in temperate regions, where there is a longer sunrise and sunset, would be greener than those in tropical regions. No-doubt, factors such as how shaded an area the plants grow in, and how much of the time is the sky above them overcast, would also have an impact upon this.
What may be particularly an issue is the colour if light in winter, when those plants that are well away from the equator would be suffering a severe shortage of light.
George
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Plant consist several type of chlorophyll, chlorophyll a and b, and another type of chlorophyll caroteinoid, which concentrate on absorbing red part of spectrum.
The question might be that if photosynthesis requires light energy, why isn't plant black. I think by absorbing more solar energy there is a counter-effect on the efficiency of photosynthesis. Too much energy have destructive effect on plant cell, to lessen the effect plant carry out photorespiration which uses up the excess light energy.
Detail of photorespiration ...I've forgotten. But it's a energy wasting process and many plants try to reduce this by alternative pathway, which give rise to C4 cycle (used by maize plant...etc to increase efficient use of light and CO2) and Crassulacaen Acid Metabolism (CAM cycle) used by plants in drier or harsher condition such as catti. The two pathway is aim to concentrate CO2 in plant cell and reduce photorespiration
We were taught this in the biochem module but er.. I wasn't paying too much attention by the end of year, so the information might be wrong.
Tom
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quote:
Originally posted by chris
I have just received an email from Dirk at Stanford in the US.
His question really intrigued me because I can't answer it. Maybe someone here can help me?
Here it is:
"I have a simple question that's been bothering me for a while. Why are most plants green? Sure, it's because chlophyll rejects green, but why does it?
The green part of the solar spectrum is the most intense. It seems like a waste to reject it."
Chris
Great minds think alike [:)]
http://www.thenakedscientists.com/forum/topic.asp?TOPIC_ID=2993&SearchTerms=GREEN,NOT,BLACK
A possible answer is that the ancestors of modern plants evolved in purple oceans:-
http://www.rsc.org/chemistryworld/News/2005/October/06100502.asp
In purple light green plants appear black, like an efficient solar cell should.
-
If you look at conifers that live in nothern lattitudes their leaves are a lot darker than more tropical plants, I don't know if this is due to chlorophyls or another pigment.
-
Maybe plants just don't like red
Brand new forum at
http://beaverlandforum.y4a.net
More than just science
-
quote:
Originally posted by chris
Thanks Eth.
I'm not sure I agree with your point about water. Red is strongly absorbed / scattered by water, blues and greens much less-so. That's why blood from cuts (or even shark attacks) looks a bizarre dark colour underwater. So ideally, by your argument, aquatic plants should absorb green and reject red wavelengths.
Chris
"I never forget a face, but in your case I'll make an exception"
- Groucho Marx
Just thinking on the hoof, so to speak.
Photosynthesis needs light, but it also requires CO2, and requires to be able to dispose of O2.
Could it be that in the depths of the oceans, there is either a deficit of CO2, or a risk of too high a buildup of O2; and so it makes sense to switch off photosynthesis as one gets deeper.
Another issue to consider is how many hours of the day is the light available. Blue/green peeks around midday, but reds are available far further into the extremities of the day, the dawn and the dusk.
George
-
Seaweed of course uses a different reddey version of chlorphyl, which must mean that it absorbs the blues and greens which travel through water the best, which makes sense.
All the green sea plants are based quite shallow, so I suppose that green chlorophyl must have some advantage if you get the whole spectrum, but I don't know what.
-
quote:
Originally posted by daveshorts
Seaweed of course uses a different reddey version of chlorphyl, which must mean that it absorbs the blues and greens which travel through water the best, which makes sense.
All the green sea plants are based quite shallow, so I suppose that green chlorophyl must have some advantage if you get the whole spectrum, but I don't know what.
I think both of my suggestions could apply to this.
That green plants tend to grow near the surface would indicate they know where the surface is, and if the use the colour of light to tell them when they are near the surface, then this would certainly be one way of doing it.
Beyond that, as I suggested, maybe the number of hours of daylight in each spectrum might make a difference. If this is the case, then it should imply that plants in temperate regions, where there is a longer sunrise and sunset, would be greener than those in tropical regions. No-doubt, factors such as how shaded an area the plants grow in, and how much of the time is the sky above them overcast, would also have an impact upon this.
What may be particularly an issue is the colour if light in winter, when those plants that are well away from the equator would be suffering a severe shortage of light.
George
-
Plant consist several type of chlorophyll, chlorophyll a and b, and another type of chlorophyll caroteinoid, which concentrate on absorbing red part of spectrum.
The question might be that if photosynthesis requires light energy, why isn't plant black. I think by absorbing more solar energy there is a counter-effect on the efficiency of photosynthesis. Too much energy have destructive effect on plant cell, to lessen the effect plant carry out photorespiration which uses up the excess light energy.
Detail of photorespiration ...I've forgotten. But it's a energy wasting process and many plants try to reduce this by alternative pathway, which give rise to C4 cycle (used by maize plant...etc to increase efficient use of light and CO2) and Crassulacaen Acid Metabolism (CAM cycle) used by plants in drier or harsher condition such as catti. The two pathway is aim to concentrate CO2 in plant cell and reduce photorespiration
We were taught this in the biochem module but er.. I wasn't paying too much attention by the end of year, so the information might be wrong.
Tom
-
quote:
Originally posted by chris
I have just received an email from Dirk at Stanford in the US.
His question really intrigued me because I can't answer it. Maybe someone here can help me?
Here it is:
"I have a simple question that's been bothering me for a while. Why are most plants green? Sure, it's because chlophyll rejects green, but why does it?
The green part of the solar spectrum is the most intense. It seems like a waste to reject it."
Chris
Great minds think alike [:)]
http://www.thenakedscientists.com/forum/topic.asp?TOPIC_ID=2993&SearchTerms=GREEN,NOT,BLACK
A possible answer is that the ancestors of modern plants evolved in purple oceans:-
http://www.rsc.org/chemistryworld/News/2005/October/06100502.asp
In purple light green plants appear black, like an efficient solar cell should.
-
If you look at conifers that live in nothern lattitudes their leaves are a lot darker than more tropical plants, I don't know if this is due to chlorophyls or another pigment.