Previous questions have addressed whether a large active animal could run off photosynthesis alone and the answer seems to be no and that it could only provide around 4% of the animals daily usage but I was wondering if they had black photosynthetic pigments and a large surface area (compared to humans and cows which the questions referred to) could this provide all or a higher percentage of their energy?

The creature can be similar to a solar powered sea slug, in that it sucks out the chloroplast from algae but in this case the black photosynthetic pigments from plant life that survive in very dimly lit habitats (possibly a cave system or dark side of a tidally locked planet etc) so have evolved black pigments to capture as much light as possible. The symbiont creature lives outside of the dimly lit habitat and can be exposed to the full sunlight, hopefully providing it enough energy for its larger size and active life.

The creatures that I had in mind were small foragers that spend time on rocks or the sides of trees basking in the sun to large flying creatures that ride the jet streams, all of the species will either have a large surface area flattened body or like the flying type and others can extend skin flaps or areas of their body to increase their surface area to receive more light. All of the creatures are relatively slow moving or spend as least energy as possible but many have the ability for bursts of energy when needing to escape a predator or catch prey. I had foraging and catching prey in mind for those that can't meet their full energy requirements from photosynthesis.

I have read about some reasons why black pigments don't exist in plants, from they don't need to as evolution has meant that the visible light wavelengths are all they need, upper layer black pigments would take all the light so lower layers would receive non and things about the electron transfer process which I don't fully understand but black pigments seem like something that with the right evolutionary pressures could exist.

Would black photosynthetic pigments and a relatively large surface area body allow theses creatures to survive from photosynthesis alone or if not all, what percentage of their daily energy needs could it provide?

  • 1
    $\begingroup$ If you mean on Earth, then the amount of light is not the limiting factor; photosynthetic output is limited first by the extremely small fraction of carbon dioxide in the air and second by the very large percentage of free oxygen in the same air. If you need to increase photosynthetic production you first need to increase the amount of carbon dioxide (about five times more is best), and second to reduce the amount of oxygen (about half will do nicely). (And I really don't see how an active animal could have a significantly larger surface area without sacrificing structural integrity.) $\endgroup$
    – AlexP
    Jun 10, 2022 at 15:29
  • $\begingroup$ @AlexP Increasing carbon dioxide makes sense. A bird with open wings has a large surface area, some of the smaller creatures are shaped like a woodlouse, so they have a spherical ish flattened shape, compared to other insects the flattened spherical shape has more surface area facing upwards. $\endgroup$
    – user96631
    Jun 10, 2022 at 15:53
  • $\begingroup$ Significantly larger surface area. You don't need a factor of 2 or 3, you need at least an order of magnitude. Animals consume a lot of energy moving around and reacting quickly to the world around them. Doubly so if they are warm blooded. $\endgroup$
    – AlexP
    Jun 10, 2022 at 16:01
  • 2
    $\begingroup$ @AlexP If you just need energy, CO2 is not required. Photosynthesis is limited by CO2 availability, but just running a photosystem to generate ATP instead of burning glucose for ATP, and not synthesizing more glucose with it, is entirely possible. Alternately, an animal can recycle CO2 that's internally generated by non-photosynthetic tissues, rather than being limited by atmospheric sources. $\endgroup$ Jun 10, 2022 at 17:26
  • $\begingroup$ it works for sea slugs because sea slugs are incredibly low energy animals. $\endgroup$
    – John
    Jun 10, 2022 at 20:04

2 Answers 2


Let us calculate an energy budget for a creature with an amazing pigment that can capture a lot of light energy.


Irradiance on Earth's surface

Average annual solar radiation arriving at the top of the Earth's atmosphere is roughly 1361 W/m2.[30] The Sun's rays are attenuated as they pass through the atmosphere, leaving maximum normal surface irradiance at approximately 1000 W/m2 at sea level on a clear day.

One watt is 1 joule per second. Let us say 1000 watts / meter squared is available to your creature which happens to have a surface area of 1 meter squared.


How to Convert Watts to Kilocalories Per Hour To convert a watt measurement to a kilocalorie per hour measurement, multiply the power by the conversion ratio.

Since one watt is equal to 0.860421 kilocalories per hour, you can use this simple formula to convert: The power in kilocalories per hour is equal to the watts multiplied by 0.860421. So 860 sunlight kilocalories / hour.

That is a lot of available energy! A banana has 105 kcal. But the 860 is with 100% efficient conversion. Photosynthesis as we know it is about 10% efficient at converting energy to usable calories. A solar panel is about 20%. If we say your creature is as good as a 1 meter squared solar panel (that it somewhat resembles) that gives 860 * 0.2 = 178 kcal / hour, *12 hours of sun = 2136 over the day. 2136 is enough calories to power a human for a day!

Here is a scheme to sidestep pesky things like breathing or needing CO2. Your creature does neither. It uses only anaerobic glycolysis stopping oxidation at pyruvate.


How Light Reactions of Photosynthesis in C4 Plants Are Optimized and Protected under High Light Conditions

Red X added by me.

This creature contents itself with only 20% of its available calories. In exchange it recycles its carbon, never oxidizing it to CO2.

Maybe your creature can do oxidative metabolism when it has to and get a sudden burst of speed and CO2 bubbles. It would do this under circumstances of need and available oxygen. It would then need to regenerate its carbon stores - which might be the occasion for the burst of speed. Maybe it saw some fine carbon and reduced nitrogen it could catch to eat.


Extrapolating from the below articles. and granted even in those, the lack of real research on earth based plant photosynthetic efficiency. The theoretical maximal photosynthetic energy conversion efficiency is less than >%10 even with genetic manipulation. Potentially you may be able to get some type of land creature in well illuminated environment. But it would still be along the lines of a jellyfish in complexity. Some movement and limited sensory organs. Touch pressure sensations, Light detection. But brains, even simple ones are energy hungry and probably out of the grasp of an organism that relies on photosynthesis alone. Photosynthesis + some other food source, perhaps only relying on sunlight during a dormant state only could be a possibility?

Light of any color from deep violet through the near-infrared could power photosynthesis. Around stars hotter and bluer than our sun, plants would tend to absorb blue light and could look green to yellow to red. Around cooler stars such as red dwarfs, planets receive less visible light, so plants might try to absorb as much of it as possible, making them look black. source

Green, yellow or even red-dominant plants may live on extra-solar planets, according to scientists whose two scientific papers appear in the March issue of the journal, Astrobiology. The scientists studied light absorbed and reflected by organisms on Earth, and determined that if astronomers were to look at the light given off by planets circling distant stars, they might predict that some planets have mostly non-green plants. source

Take, for example, the fact that it’s possible that plants are actually the wrong colour, at least in terms of photosynthetic efficiency. As attractive as green fields and forests are to the human eye, to those in the know, they represent a scandalous waste of sunlight. Plants are green because chlorophyll reflects, rather than absorbs, the middle of the light spectrum. Chlorophyll powers the photosynthetic reaction by absorbing and transferring energy from light, but, according to Nick Lane, an evolutionary biochemist speaking on Melvyn Bragg’s programme, it only absorbs blue and red light — and, worse yet, it only actually bothers using the red stuff, which is the lower energy of the two.Source

  • 1
    $\begingroup$ This doesn't answer the question. Also plants on planets around hotter stars may likely have light/ close to white leaves to reflect the excess light, rather than being other colours. $\endgroup$
    – user96631
    Jun 10, 2022 at 14:40
  • $\begingroup$ Apologies @SimonDiamond, Im at work, mistakenly submitted when I was called to duty. Have edited the answer. $\endgroup$
    – Gillgamesh
    Jun 10, 2022 at 15:46

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