4 ms·

> Yes, but why? Scientific writing style is not always very good at highlighting the unknowns. "We don't know this" doesn't make very convincingly looking text

by sampo 1y ago

> Yes, but why? Scientific writing style is not always very good at highlighting the unknowns. "We don't know this" doesn't make very convincingly looking text, so people tend to avoid admitting it up front. But you are, of course, correct to ask. Like another comments said, this is an open question. One theory is, that while the algae floating in water were absorbing broad spectrum, the algae growing attached at the bottom of the water evolved to chlorophyll to capture whatever was left at the edges of the spectrum. And then later land-based plants would have evolved from the water plants that were already attaching themselves to the bottom. But then why are also the current ocean-floating algae green now? http://hyperphysics.phy-astr.gsu.edu/hbase/Biology/imgbio/plantblack.png http://hyperphysics.phy-astr.gsu.edu/hbase/Biology/imgbio/pl... Another theory is that a perfectly-absorbing leaf would somehow absorb too much energy and get overheated, and that it was better to absorb only part of the available light. None of these theories are fully convincing, so the question remains open.

enopod_ 1y ago
According to the article, at least todays retinal-based photosynthesis is anoxygenic and does not invole carbon fixation. At night, these cells metabolism stops. Chlorophyllic photosynthesis with attached carbon fixation allows the cell to build up starch during the day, which it breathes under the use of oxygen at night, so the cell remains active during the night. Looks like a big evolutionary advantage to me. Also, light is not the limiting factor for plant growth, it‘s usually water or nutrient availability.
- throwawaymaths 1y ago
  carbon fixation is a completely separate process. in principle you could hook up a sufficiently engineered cell to electrodes and do the carbon fixation part in the dark by supplying it with juice from the mains. accordingly there is no particular reason for purple photon assimilation to not be attached to carbon fixation... though i suppose as the electron energy levels dont quite match up it might be a schlep to get purples to make sugar.
tbrownaw 1y ago
> "We don't know this" doesn't make very convincingly looking text, so people tend to avoid admitting it up front. Saying definitively that we don't know something (1) requires an investment of time to verify that lack of knowledge, and (2) can become incorrect at any time. If you want to do something with the answer but find that it doesn't exist, sure make a note of that to request that someone could maybe try to find out. But if it's just a curiosity rather than directly relevant, why bother?
- khfsoc 1y ago
  > Saying definitively that we don't know something (1) requires an investment of time to verify that lack of knowledge, and (2) can become incorrect at any time. And (3) doesn’t necessarily make you lose credibility but too many believe it does and partially it can. Those who believe science is truth are innocently choosing an answer without full knowledge. That is the definition of religion and faith. True science is a search for truth like philosophy and theology. I think you can get too caught up in any one of these three. If you have hard core faith, that’s awesome, but put your faith into that which won’t fail you.
  - prerok 1y ago
    I am sorry but I don't quite agree with you. In science, there is clear delineation between things we know to be true (laws), things that appear to be true based on our current knowledge (theories) and things that may or may not be true but seem to be true based on limited data/limited research (hypotheses). I don't think the three (I only see two, though, but don't want to nitpick) approaches are really comparable.
    - vcvitae 1y ago
      Scientific laws are not solid. Newton's First Law (Law of Inertia) – assumes objects remain at rest or in uniform motion unless acted upon by an external force; inaccurate in non-inertial (accelerating) frames without fictitious forces. Newton's Second Law – assumes constant mass and low velocities; inaccurate at relativistic speeds where mass increases with velocity. Newton's Third Law – inaccurate in electromagnetic, quantum, or relativistic contexts. Newton's Law of Universal Gravitation – assumes instantaneous action at a distance and weak fields; replaced by General Relativity in strong fields or at high velocities. Boyle's Law – inaccurate at high pressures, low temperatures, or with real gases, which deviate from ideal behavior. Charles's Law – assumes ideal gas behavior; deviations occur at high pressures or low temperatures. Ohm's Law – assumes constant resistance; inaccurate for non-ohmic materials like diodes or at high voltages where resistance varies. 2nd Law of Thermodynamics – inaccurate with fluctuations at microscopic scales, temporarily decreasing entropy. Kepler's Laws – inaccurate when considering relativistic effects. Laws of Motion of Fluids (e.g., Bernoulli's Law) – assumes incompressible, non-viscous flow; inaccurate for real fluids with viscosity or compressibility effects. Dalton's Law of Partial Pressures – assumes gases do not interact; inaccurate at high pressures or with strong intermolecular forces. Fick's Laws of Diffusion - inaccurate in complex systems with reactions or non-constant diffusion coefficients. Laws of Electromagnetic Induction (Faraday's Law) – assumes ideal conditions; real systems have hysteresis and other non-ideal effects. Laws of Radioactive Decay – exponential decay is inaccurate as does not fully regard environment or decay chain complexities.
Etherlord87 1y ago
How about this: it takes energy to build a photo-synthesis machine. A machine like this won't consume all photons but only some range of electromagnetic spectrum. This is because you need to have such structure to allow light to pass through the outer part of the body of the organism, but be absorbed at a very specific place inside. This is why multi-junction solar cells exist, to use more of the solar spectrum. It would cost a plant more energy to build such a multi-layered chloroplast, so perhaps having just a single layer using a single range of the spectrum is the most optimal (at least as a local maximum).
flockonus 1y ago
> Another theory is that a perfectly-absorbing leaf would somehow absorb too much energy and get overheated If having both pigments means the plant would be close to black, overheating is an absolutely valid hypothesis imo, plants just like animals have optimal temperature metabolism and often getting too hot is deadly, while under optimal temperature is tolerable.
- geokon 1y ago
  sure but there are probably ecological niches that are light starved. for instance deeper in the water column or in dark areas like caves or polar regions
  - Theodores 1y ago
    Evolution is only possible along certain paths, for example, we are not going to evolve to have more than four limbs, eyes at the back of our heads or extra hands. Similarly, at the cell level, we have just the one photosynthesis process in plants and that isn't going to take an entirely different path to work on different wavelengths. The evolutionary investment is in chlorophyll with a magnesium element at the heart of it. Imaginably you would need an entirety different molecule with some other magic atom in the middles of the usual organic chemistry and that isn't going to happen given the sunk cost in the chlorophyll way of doing things. There is a greater chance that we will get six hands than that happening.
  - prerok 1y ago
    Indeed, and frequently you will see that leaves are a much darker hue of green than the ones exposed directly to sunlight. So, using the same mechanism, still more is absorbed if light is scarce.
  - flockonus 1y ago
    Of course, for example several sea weeds come to mind in dark green to brown tones; which makes sense, they can disperse heat very fast since they are immersed in cold water / liquid cooling

by sampo 1y ago

enopod_ 1y ago

According to the article, at least todays retinal-based photosynthesis is anoxygenic and does not invole carbon fixation. At night, these cells metabolism stops. Chlorophyllic photosynthesis with attached carbon fixation allows the cell to build up starch during the day, which it breathes under the use of oxygen at night, so the cell remains active during the night. Looks like a big evolutionary advantage to me. Also, light is not the limiting factor for plant growth, it‘s usually water or nutrient availability.

throwawaymaths 1y ago
carbon fixation is a completely separate process. in principle you could hook up a sufficiently engineered cell to electrodes and do the carbon fixation part in the dark by supplying it with juice from the mains. accordingly there is no particular reason for purple photon assimilation to not be attached to carbon fixation... though i suppose as the electron energy levels dont quite match up it might be a schlep to get purples to make sugar.

tbrownaw 1y ago

> "We don't know this" doesn't make very convincingly looking text, so people tend to avoid admitting it up front. Saying definitively that we don't know something (1) requires an investment of time to verify that lack of knowledge, and (2) can become incorrect at any time. If you want to do something with the answer but find that it doesn't exist, sure make a note of that to request that someone could maybe try to find out. But if it's just a curiosity rather than directly relevant, why bother?

khfsoc 1y ago
> Saying definitively that we don't know something (1) requires an investment of time to verify that lack of knowledge, and (2) can become incorrect at any time. And (3) doesn’t necessarily make you lose credibility but too many believe it does and partially it can. Those who believe science is truth are innocently choosing an answer without full knowledge. That is the definition of religion and faith. True science is a search for truth like philosophy and theology. I think you can get too caught up in any one of these three. If you have hard core faith, that’s awesome, but put your faith into that which won’t fail you.
- prerok 1y ago
  I am sorry but I don't quite agree with you. In science, there is clear delineation between things we know to be true (laws), things that appear to be true based on our current knowledge (theories) and things that may or may not be true but seem to be true based on limited data/limited research (hypotheses). I don't think the three (I only see two, though, but don't want to nitpick) approaches are really comparable.
  - vcvitae 1y ago
    Scientific laws are not solid. Newton's First Law (Law of Inertia) – assumes objects remain at rest or in uniform motion unless acted upon by an external force; inaccurate in non-inertial (accelerating) frames without fictitious forces. Newton's Second Law – assumes constant mass and low velocities; inaccurate at relativistic speeds where mass increases with velocity. Newton's Third Law – inaccurate in electromagnetic, quantum, or relativistic contexts. Newton's Law of Universal Gravitation – assumes instantaneous action at a distance and weak fields; replaced by General Relativity in strong fields or at high velocities. Boyle's Law – inaccurate at high pressures, low temperatures, or with real gases, which deviate from ideal behavior. Charles's Law – assumes ideal gas behavior; deviations occur at high pressures or low temperatures. Ohm's Law – assumes constant resistance; inaccurate for non-ohmic materials like diodes or at high voltages where resistance varies. 2nd Law of Thermodynamics – inaccurate with fluctuations at microscopic scales, temporarily decreasing entropy. Kepler's Laws – inaccurate when considering relativistic effects. Laws of Motion of Fluids (e.g., Bernoulli's Law) – assumes incompressible, non-viscous flow; inaccurate for real fluids with viscosity or compressibility effects. Dalton's Law of Partial Pressures – assumes gases do not interact; inaccurate at high pressures or with strong intermolecular forces. Fick's Laws of Diffusion - inaccurate in complex systems with reactions or non-constant diffusion coefficients. Laws of Electromagnetic Induction (Faraday's Law) – assumes ideal conditions; real systems have hysteresis and other non-ideal effects. Laws of Radioactive Decay – exponential decay is inaccurate as does not fully regard environment or decay chain complexities.

Etherlord87 1y ago

How about this: it takes energy to build a photo-synthesis machine. A machine like this won't consume all photons but only some range of electromagnetic spectrum. This is because you need to have such structure to allow light to pass through the outer part of the body of the organism, but be absorbed at a very specific place inside. This is why multi-junction solar cells exist, to use more of the solar spectrum. It would cost a plant more energy to build such a multi-layered chloroplast, so perhaps having just a single layer using a single range of the spectrum is the most optimal (at least as a local maximum).

flockonus 1y ago

> Another theory is that a perfectly-absorbing leaf would somehow absorb too much energy and get overheated If having both pigments means the plant would be close to black, overheating is an absolutely valid hypothesis imo, plants just like animals have optimal temperature metabolism and often getting too hot is deadly, while under optimal temperature is tolerable.

geokon 1y ago
sure but there are probably ecological niches that are light starved. for instance deeper in the water column or in dark areas like caves or polar regions
- Theodores 1y ago
  Evolution is only possible along certain paths, for example, we are not going to evolve to have more than four limbs, eyes at the back of our heads or extra hands. Similarly, at the cell level, we have just the one photosynthesis process in plants and that isn't going to take an entirely different path to work on different wavelengths. The evolutionary investment is in chlorophyll with a magnesium element at the heart of it. Imaginably you would need an entirety different molecule with some other magic atom in the middles of the usual organic chemistry and that isn't going to happen given the sunk cost in the chlorophyll way of doing things. There is a greater chance that we will get six hands than that happening.
- prerok 1y ago
  Indeed, and frequently you will see that leaves are a much darker hue of green than the ones exposed directly to sunlight. So, using the same mechanism, still more is absorbed if light is scarce.
- flockonus 1y ago
  Of course, for example several sea weeds come to mind in dark green to brown tones; which makes sense, they can disperse heat very fast since they are immersed in cold water / liquid cooling