Spring has sprung, and my brain came up with: is a plant a plant because it has green (chlorophyll), sort of by definition?
Thinking more about green, I wondered about “a just ok green” vs some other frequency “super-duper green” which for a given area produces more energy. Then I thought that of course the whole system can work together to increase the energy generated, even given a relatively “inefficient” energy absorber.
So, “bang-for-the-buck” means as a frequency/area unit of where the sun hits the green stuff, or as a plant as a whole, can “efficiency” be discussed in any coherent units?
There are certainly non-plant organisms that photosynthesize (cyanobacteria, for starters), and I’m pretty sure that there are some plants that don’t photosynthesize, or at least photosynthesize very little (they’re parasites that fill a similar niche as fungi).
Plants don’t necessarily have chlorophyll, seeing as they can be parasitic, living off other plants’ chlorophyll (i.e. dodders and Indian pipe).
I haven’t heard of any quantitative ways to measure this, but in general variegated plants with green and white foliage are not as vigorous as their all-green counterparts.
There are also chlorophyll-free plants (saprophytes) that “eat” decomposing matter in the soil. Pine drops, snow plant, and several types of orchids, to name a few.
I read it as asking whether there is an ideal shade of green to maximize the energy return on photosynthesis. Not that I can answer that particular question.
I don’t have an answer for the efficiency question, but I’ll note that plants are green because that’s the color of light that they don’t use. They reflect the “waste” light, and absorb the other colors as they photosynthesize.
Yeah, but the problem with questions of efficiency is that you have to define what you mean by efficient. Total energy efficiency, overall cost efficiency, use of space, mass, some combination, and do you just need pure sugar and oxygen, or do you need vitamins and lipids and cellulose and so forth?
In a closed system, red and blue light in combination are the most effective at stimulating metabolic activity. But most places on earth, it can’t compete on a dollar basis with sunlight, which is very nearly free. Similarly, algae has the lowest overhead in terms of non photosynthetic mass. But if you try growing it in the ocean, you’ll quickly find much of your crop eaten by the critters living there. Despite that it could still be the most efficient option if all you want is oxygen production.
We can answer any number of plausible interpretations of the question, but there’s no ‘right’ answer until the question is pinned down a bit more.
Ornamental plum trees have purple leaves, and use anthocyanin to get energy from sunlight. They also use chlorophyll but the high levels of anthocyanin keeps the leaves from being green.
Thanks to all. The first part of OP I’ll have to take up with Linnaeus, or whoever it was, besides God, who decided what makes a plant.
Obtenebrate nails the bang-for-the buck part of OP. I knew so many different conditions/costs/benefits must exist in such a complicated system, but didn’t know where to start.
About green being the color that isn’t: thanks, of course, and it was silly of me to put it that way. Don’t humans have particularly acute retina receptors in the green areas? [Warning: Finnegans Wake cite perhaps in a subsequent post]
I thought someone else might have been along to educate us; perhaps they will, but in the meantime I might as well put down what I can remember.
Chlorophyll is not the only photosthesising pigment, although it is the most common one; there are bacteria that use a form of rhodopsin, the sort of pigment we use in our retinas to convert light into nerve impulses.
it may be the case that life on some other planet out there has never evolved chlorophylls, so would rely on the rhodopsins for their metabolism. But this would be much less efficient.
Many forms of Algae use additional pigments to gather more energy, although they use chlorophyll fr the main event; these pigments, called accessory pigments, allow algae to live deeper beneath the waves.
Fucoxanthin gives brown algae their colour,
while phycobiliproteins give red algae their colour.
Maybe plants on another planet around a different star would use some, or several, of these accessory pigments to gather more light energy. I suspect, but can’t prove, that chlorophylls aren’t the only option for photosynthesis, and maybe these other light-collecting compounds will have their own accessory pigments, creating a very wide possible range of plant colours.
It’s black, but I dont think it’s any more photosynthetic as a result. It’s absorbing more visible light than some other green plants, but not necessarily making food with it.
