Why are leaves green?

[MrMistery]

I said generally guys...
Yes there are two basic cases when "sharing" (what is actually called altruism) is good:
Kin altruism - when the two organisms share part of their alleles the reproduction of one will actually increase the fitness of the other, because it passes down genes they both have. From this you can derive the "two brothers or eight cousin case" postulated by G.B.S. Haldane, in that the minimum people you should be altruistic is is either two brothers or 8 cousins, as that is equivalent with 100% of your genes.
Reciprocal altruism - what you described with the bats. I think my old textbook had the same example, though it's been a few years. From what I remember, some of the bats stick around the cave because they need to take care of the young. The adult bats take turns in gathering food, and also feed the "baby-sitters" when they return.
About humans, it is a bit complicated: if a man is risking his life to save a complete stranger, then he is apparently risking his life to save completely different genes for no good reason. Generally in the human population this kind of altruism is never reciprocated, so i find it hard to examine how human altruism can be evolutionary good, at least in some cases. Nor do I care really.
About plants: I do not believe reciprocal altruism to be the case here, with the advent of green-reflecting pigments. It is still possible, but I honestly doubt it. In most ecosystems photosynthetic organisms are in terrible competition with each other for light, and I see no reason why this was not true when photosynthesis was just emerging.
I have to say I am not a physicist. The explanation I gave I learned from a botany book. If you think that does not agree with physics, I would be more than happy to listen to your opinions as to why not.
BTW, here is a person who apparently did some research on the topic: http://theforcethat.blogspot.com/2007/0 ... green.html

[Sumi]

I learned from a photovoltaic (PV) manufacturer that PV has over-heating problems. Commonsense tells me that to increase the energy output of PV, you can just increase the amount of light. I did this using a mirror. Doubling the amount of light increased the electrical output of PV but also it made the PV panels very hot. Hot PV fails for its wiring and other electrical systems.

A tree’s interest is to gain most amount of energy from the sunlight. It does not want to get fried in the process. Although black may be the logical color, the cooling system does not keep the leaves cool enough. Leaves have limited amount of air and water cooling mechanism. The nature’s solution is to collect some energy at the first layer of leaves, let the rest of the energy go through and catch them at the second layer of the leaves and so on. This does not overheat the leaves.
But why green?

I saw an experiment at a students’ science fair that compared the energy going through various colored glass. It was a simple experiment of placing a PV at the bottom with a light bulb at top, placing different colored glass plates in between. Green allowed the least amount of energy to go though next to black. In another word, green is the best color to collect energy but not overheating the leaves. By having the secondary layers of leaves, trees achieve their goal of the most effective energy collection.

[wrong16]

The leaves contain chlorophyll which is green in colour.
Mostly leaves make up of MOST chlorophyll out of all other pigment make the leave green,
and they reflect the green light (thus they appears green) and abosorb other lights.

This chlorophyll carries out photosynthesis: food making process; take in carbon dioxide and give out oxygen. Changes light energy to food. Only carries out when there is light, water and carbon dioxide.

The higher rate of photosynthesis and absorbance by green leaves are
in the red (chlorophyll a: 650 nm) and violet light (chlorophyll b : 400 nm) range.
While the lowest is green which is reflected and minimal green light is also absorbed.
[ more information check out Action & Absorption Spectra]

My opinion is :
"It not only about the 'quality' of light ; how much energy it gives"
"it is also about the quantity that is absorbed and make use of."

If it has two higher reading for violet and red wavelenght (which they absorbed and make use of)
red is kinda the longest, lowest energy wavelengths and
violet is kinda the shortest and highest energy wavelengths.

and green (510 nm) is in between of them.
so what do you think now ?

[MrMistery]

so why is it better to be in the middle?

[sanjid123]

leaves are green for the present of chlorophyll pigment and i hope everyone knows it well. I understood that english is not you 1st language and also mine as well.

[Linn]

I agree with that herb86, many photosynthetic plants /algae found some distance below the surface contain red pigments so that they can utilize the red wavelength, which is basically almost the only light wavelength that can reach deeper waters.

Another thing, many scientists believe that sometime in the past, chloroplasts are actually living cells that have been engulfed or had symbiotic relationship with other cells. This will explain why chloroplasts and mitochondria have their own DNA that is separate from the genomic DNA of photosynthetic cells.

So its possible that in the past, if these chloroplast ancestors were predominantly green pigmented, the leaf color that we see now are simply a carry over charateristic of those cells.

This would seem to make sense since many plant leaves with red pigments are found as understory plants, however it's not always the case as many are found growing in full sun.

[MrMistery]

it also depends on what "red pigments" you are considering.
The red pigment mkwaje was referring to is phycoerythrin, which indeed has the role to allow the organism to use light that would otherwise be useless. However, most land plants that we see colored in red owe their color to anthocyan pigments. these pigments are stored in the central vacuole of a cell (and thus have absolutely nothing to do with photosynthesis) and serve the role of attracting insect and bird pollinators.

I would advise caution when using the word "pigment". While many classical biologists (especially botanists) still classify substances by their color, and refer to anything colored as "pigments", most of these pigments are very different chemically and some have entirely different roles. A chemical/biochemical classification would be much better in my opinion.

[Linn]

well I just read the original post again and realized you said that green light has the most energy.
But really it's the blue and violet light that has the most at 400 nm wavelenght, followed by green which I think is 500. Also I think, if I remember right, that some pigments do utilize the green wavelength.