5 ms·

unfortunately to meet animal energy requirements one would need a huge canopy; it'd probably only be feasible outside our gravity well.

gus_massa 2y ago
Relevant what-if-xkcd https://what-if.xkcd.com/17/ https://what-if.xkcd.com/17/
- card_zero 2y ago
  How come chlorophyll photosynthesis isn't more efficient? 6% for plants, 20% for (ordinary) solar panels. Don't plants have to outcompete other plants? Then there's red algae, which inhabit dark places like caves and the ocean, and they're apparently way more efficient. Is it somehow not advantageous to a tree to photosynthesize efficiently?
  - dekhn 2y ago
    plants only use part of the spectrum. Likely they have hit some local or maybe even global maximum that would be hard to evolve past. See https://en.wikipedia.org/wiki/Photosynthetic_efficiency https://en.wikipedia.org/wiki/Photosynthetic_efficiency
    - adrian_b 2y ago
      The terrestrial plants use only a small part of the spectrum, because the available light is frequently too abundant for them, which was even more true at the beginning of their evolution, when there were no forests providing shadows. For terrestrial plants, it is usually a more important problem to not be overwhelmed by too much energy captured from light, than to capture more. This is why the green plants dominate on continents, because they reflect a good part of the light, instead of absorbing it, so they are not destroyed by excessive light. On the other hand, in the oceans the green algae are a minority in comparison with diatoms, brown algae and other kinds of algae that absorb much larger fractions of the solar light, because they can use only the less intense light that remains after passing through water. On the bottoms of waters there are many places where there are combined algal and bacterial mats that act like a multijunction photovoltaic cell, i.e. there are multiple layers of different algae and bacteria, e.g. diatoms, blue-green algae (cyanobacteria), purple non-oxygenic phototrophic bacteria and green non-oxygenic phototrophic bacteria, so that each layer absorbs a different part of the solar light spectrum, resulting in almost complete absorption through all layers.
      - card_zero 2y ago
        You might clarify "too abundant", "overwhelmed", and "destroyed". Elsewhere, somebody told me: > one must know that chemical reactions with gases are very dependent on the pressure of the gases. Even the direction, that is if it's exothermic or endothermic, depends highly on the pressure. If RuBisCo would be faster the carbon dioxide could not come fast enough onto the site of enzymatic activity and would therefore drop in pressure there. And > Generally plants have too much energy for the amount of water and, most important, carbon dioxide, to synthesize sugar. So the idea I come away with is that CO2 is not abundant enough for the energy (that a differently-made plant could extract from the light) to be useful.
        gus_massa 2y ago
        Can a plant near a volcano get a boost? How fast can plants (or gree algae) evolve to absorb the increased CO2 in the air?
        card_zero 2y ago
        That is a fun question. Like life around hydrothermal vents, but on land. I can't search for answers easily because of course volcanic soil is really fertile anyway, so people have plenty to say about plants that grow around volcanos already, without reference to carbon dioxide.
        adrian_b 2y ago
        That is correct. By overwhelmed, I have meant exactly this, i.e. if the terrestrial plants had captured more solar energy, the only effect would have been the accumulation in their cells of free oxygen and of intermediate reduced chemical compounds that could not be used fast enough to synthesize useful substances like carbohydrates, for various reasons, of which the lack of enough captured carbon dioxide is a major reason. The capture of carbon dioxide can be hampered by the free oxygen produced by capturing solar light, even if the plant cells attempt to separate the cell parts where these incompatible processes occur. It might be possible to improve the productivity of the plants by improving their ability to capture carbon dioxide, more than by improving their ability to capture light. However I believe that such research directions are misguided. We are already able to capture light very efficiently with non-biological devices and the same is likely to become true for carbon dioxide capture and electrolytic reduction. What is unlikely to happen any time soon is to find any way for synthesizing complex organic molecules like those needed for food as efficiently as by using living cells. So the non-biological capture of solar energy and capture and reduction of carbon dioxide and dinitrogen should be combined with biological syntheses in cultivated organisms.
  - gus_massa 2y ago
    I think efficiency of plants, but that's measure from light to sugar that is a good long term storage material. Solar panels get 20% but you get electricity that is difficult to store. Some plants have slightly better efficiency https://en.wikipedia.org/wiki/C4_carbon_fixation https://en.wikipedia.org/wiki/C4_carbon_fixation but not too much. I think you linked an article about red algae. I took a look and I think they are counting the efficiency in a strange way to claim "almost 100%". Probably almost 100% in the first step of capturing the energy, not in the complete process to transform it into something useful. (And probably using only monochrome light, but I can't understand the details)
    - card_zero 2y ago
      Oh, I removed that link because it was talking about efficiency of light transmission to reaction centers, or something like that, i.e. only the start of the process. And you're quite right, I wasn't even looking at the whole process myself, I'd need to consider a solar-powered carbon-fixing, uh, plant. As in industrial plant.
      - gus_massa 2y ago
        I agree.
  - d_silin 2y ago
    You got me thinking about incorporating silicon-based photosynthesis chemistry into plants. Making that work would be tricky, for sure.
    - adrian_b 2y ago
      The solution is not incorporating photovoltaic cells into living plants. The most efficient way of making food and other complex organic molecules is to make artificial devices that would use solar panels and which would use the energy to capture both carbon dioxide and nitrogen from the air (possibly also water from the air humidity) and which would make ammonia and some very simple organic molecule. Whatever is produced with solar energy, could be used as food for some genetically modified fungi or other similar organisms (e.g. genetically modified parasitic plants). These genetically modified living organisms would perform all the complex enzymatic syntheses required to make food suitable for humans or any other complex organic substances of interest. Some time in the future it should become possible to create a fungus (or a parasitic plant) capable of growing not only mushrooms, but also bananas, wheat grains, chicken eggs, turkey thighs or whatever else one could want to harvest from such a culture. So the coupling between solar panels and some culture of living beings should be external, through food. This has the advantage that the surface would be occupied only by the solar panels and the associated chemical reactors that would store the solar energy into simple organic molecules and ammonia (possibly combined in a simple amino-acid like glycine), while making food could be done e.g. in underground facilities and only when needed and producing only whatever is in demand at a given time.
culi 2y ago
You're thinking entirely replacing our energy source. What about just boosting it passively. Imagine if energy requirements for every human were decreased by 2%
- simcop2387 2y ago
  Probably not dolable on planetary scale but ii imagine it'd help in space, esp if combined with some other mods like fiximg the vitamin c gene to remove scurvy. If we could use light to suppliment our metabolism it'd mean fewer physical resources to bring alon.
  - euroderf 2y ago
    > fixing the vitamin c gene to remove scurvy There's other possible fixes too. For starters, Vitamin D?
- 082349872349872 2y ago
  > Imagine if energy requirements for every human were decreased by 2% Taking the spherical human to require 8400 kJ/day, we're talking ~170 kJ replacement, or: ~6g butter, or ~1/3 of a can of Coke, or ~1/3 of a single Bounty piece, or ~1 McNugget (without sauce) Not sure that all that biohacking would be worth the single extra smear/swig/bite?
  - manvillej 2y ago
    per day though. I think others are right that it has applications in space. going with the butter example, 5 people on a year long mission is almost 11kg you don't have to bring up to space. on an environmental perspective, if applied to everyone, its almost half a quadrillion kJ removed a year, plus supply chain logistics, waste, packaging, I still think its probably a ridiculous pipedream, but even pipedreams are meant to be dreamt.
    - pishpash 2y ago
      11kg is nothing...
PaulHoule 2y ago
The metabolic rate of an animal scales as 0.75 the mass, I guess surface area is about the 0.66 power of mass so I guess it gets more favorable when you get smaller but not by a lot. See https://book.bionumbers.org/how-does-metabolic-rate-scale-with-size/ https://book.bionumbers.org/how-does-metabolic-rate-scale-wi... Note thermal efficiency is a problem too. For instance you could imagine wearing an LED suit that exposes you to a lot of light. You need 100W for your basal metabolism, if photosynthesis were 10% efficient you'd be dealing with 900W of waste heat which is a lot, real-life efficiency would be worse than that.
- ggu7hgfk8j 2y ago
  Maybe you could combine it with some kind of hibernation to drastically reduce metabolism?

gus_massa 2y ago

Relevant what-if-xkcd https://what-if.xkcd.com/17/ https://what-if.xkcd.com/17/

card_zero 2y ago
How come chlorophyll photosynthesis isn't more efficient? 6% for plants, 20% for (ordinary) solar panels. Don't plants have to outcompete other plants? Then there's red algae, which inhabit dark places like caves and the ocean, and they're apparently way more efficient. Is it somehow not advantageous to a tree to photosynthesize efficiently?
- dekhn 2y ago
  plants only use part of the spectrum. Likely they have hit some local or maybe even global maximum that would be hard to evolve past. See https://en.wikipedia.org/wiki/Photosynthetic_efficiency https://en.wikipedia.org/wiki/Photosynthetic_efficiency
  - adrian_b 2y ago
    The terrestrial plants use only a small part of the spectrum, because the available light is frequently too abundant for them, which was even more true at the beginning of their evolution, when there were no forests providing shadows. For terrestrial plants, it is usually a more important problem to not be overwhelmed by too much energy captured from light, than to capture more. This is why the green plants dominate on continents, because they reflect a good part of the light, instead of absorbing it, so they are not destroyed by excessive light. On the other hand, in the oceans the green algae are a minority in comparison with diatoms, brown algae and other kinds of algae that absorb much larger fractions of the solar light, because they can use only the less intense light that remains after passing through water. On the bottoms of waters there are many places where there are combined algal and bacterial mats that act like a multijunction photovoltaic cell, i.e. there are multiple layers of different algae and bacteria, e.g. diatoms, blue-green algae (cyanobacteria), purple non-oxygenic phototrophic bacteria and green non-oxygenic phototrophic bacteria, so that each layer absorbs a different part of the solar light spectrum, resulting in almost complete absorption through all layers.
    - card_zero 2y ago
      You might clarify "too abundant", "overwhelmed", and "destroyed". Elsewhere, somebody told me: > one must know that chemical reactions with gases are very dependent on the pressure of the gases. Even the direction, that is if it's exothermic or endothermic, depends highly on the pressure. If RuBisCo would be faster the carbon dioxide could not come fast enough onto the site of enzymatic activity and would therefore drop in pressure there. And > Generally plants have too much energy for the amount of water and, most important, carbon dioxide, to synthesize sugar. So the idea I come away with is that CO2 is not abundant enough for the energy (that a differently-made plant could extract from the light) to be useful.
      - gus_massa 2y ago
        Can a plant near a volcano get a boost? How fast can plants (or gree algae) evolve to absorb the increased CO2 in the air?
        card_zero 2y ago
        That is a fun question. Like life around hydrothermal vents, but on land. I can't search for answers easily because of course volcanic soil is really fertile anyway, so people have plenty to say about plants that grow around volcanos already, without reference to carbon dioxide.
      - adrian_b 2y ago
        That is correct. By overwhelmed, I have meant exactly this, i.e. if the terrestrial plants had captured more solar energy, the only effect would have been the accumulation in their cells of free oxygen and of intermediate reduced chemical compounds that could not be used fast enough to synthesize useful substances like carbohydrates, for various reasons, of which the lack of enough captured carbon dioxide is a major reason. The capture of carbon dioxide can be hampered by the free oxygen produced by capturing solar light, even if the plant cells attempt to separate the cell parts where these incompatible processes occur. It might be possible to improve the productivity of the plants by improving their ability to capture carbon dioxide, more than by improving their ability to capture light. However I believe that such research directions are misguided. We are already able to capture light very efficiently with non-biological devices and the same is likely to become true for carbon dioxide capture and electrolytic reduction. What is unlikely to happen any time soon is to find any way for synthesizing complex organic molecules like those needed for food as efficiently as by using living cells. So the non-biological capture of solar energy and capture and reduction of carbon dioxide and dinitrogen should be combined with biological syntheses in cultivated organisms.
- gus_massa 2y ago
  I think efficiency of plants, but that's measure from light to sugar that is a good long term storage material. Solar panels get 20% but you get electricity that is difficult to store. Some plants have slightly better efficiency https://en.wikipedia.org/wiki/C4_carbon_fixation https://en.wikipedia.org/wiki/C4_carbon_fixation but not too much. I think you linked an article about red algae. I took a look and I think they are counting the efficiency in a strange way to claim "almost 100%". Probably almost 100% in the first step of capturing the energy, not in the complete process to transform it into something useful. (And probably using only monochrome light, but I can't understand the details)
  - card_zero 2y ago
    Oh, I removed that link because it was talking about efficiency of light transmission to reaction centers, or something like that, i.e. only the start of the process. And you're quite right, I wasn't even looking at the whole process myself, I'd need to consider a solar-powered carbon-fixing, uh, plant. As in industrial plant.
    - gus_massa 2y ago
      I agree.
- d_silin 2y ago
  You got me thinking about incorporating silicon-based photosynthesis chemistry into plants. Making that work would be tricky, for sure.
  - adrian_b 2y ago
    The solution is not incorporating photovoltaic cells into living plants. The most efficient way of making food and other complex organic molecules is to make artificial devices that would use solar panels and which would use the energy to capture both carbon dioxide and nitrogen from the air (possibly also water from the air humidity) and which would make ammonia and some very simple organic molecule. Whatever is produced with solar energy, could be used as food for some genetically modified fungi or other similar organisms (e.g. genetically modified parasitic plants). These genetically modified living organisms would perform all the complex enzymatic syntheses required to make food suitable for humans or any other complex organic substances of interest. Some time in the future it should become possible to create a fungus (or a parasitic plant) capable of growing not only mushrooms, but also bananas, wheat grains, chicken eggs, turkey thighs or whatever else one could want to harvest from such a culture. So the coupling between solar panels and some culture of living beings should be external, through food. This has the advantage that the surface would be occupied only by the solar panels and the associated chemical reactors that would store the solar energy into simple organic molecules and ammonia (possibly combined in a simple amino-acid like glycine), while making food could be done e.g. in underground facilities and only when needed and producing only whatever is in demand at a given time.

culi 2y ago

You're thinking entirely replacing our energy source. What about just boosting it passively. Imagine if energy requirements for every human were decreased by 2%

simcop2387 2y ago
Probably not dolable on planetary scale but ii imagine it'd help in space, esp if combined with some other mods like fiximg the vitamin c gene to remove scurvy. If we could use light to suppliment our metabolism it'd mean fewer physical resources to bring alon.
- euroderf 2y ago
  > fixing the vitamin c gene to remove scurvy There's other possible fixes too. For starters, Vitamin D?
082349872349872 2y ago
> Imagine if energy requirements for every human were decreased by 2% Taking the spherical human to require 8400 kJ/day, we're talking ~170 kJ replacement, or: ~6g butter, or ~1/3 of a can of Coke, or ~1/3 of a single Bounty piece, or ~1 McNugget (without sauce) Not sure that all that biohacking would be worth the single extra smear/swig/bite?
- manvillej 2y ago
  per day though. I think others are right that it has applications in space. going with the butter example, 5 people on a year long mission is almost 11kg you don't have to bring up to space. on an environmental perspective, if applied to everyone, its almost half a quadrillion kJ removed a year, plus supply chain logistics, waste, packaging, I still think its probably a ridiculous pipedream, but even pipedreams are meant to be dreamt.
  - pishpash 2y ago
    11kg is nothing...

PaulHoule 2y ago

The metabolic rate of an animal scales as 0.75 the mass, I guess surface area is about the 0.66 power of mass so I guess it gets more favorable when you get smaller but not by a lot. See https://book.bionumbers.org/how-does-metabolic-rate-scale-with-size/ https://book.bionumbers.org/how-does-metabolic-rate-scale-wi... Note thermal efficiency is a problem too. For instance you could imagine wearing an LED suit that exposes you to a lot of light. You need 100W for your basal metabolism, if photosynthesis were 10% efficient you'd be dealing with 900W of waste heat which is a lot, real-life efficiency would be worse than that.

ggu7hgfk8j 2y ago
Maybe you could combine it with some kind of hibernation to drastically reduce metabolism?