Considering the surface area of a cow and that they apparently ought to eat 14+kg of grass a day plus a few kg of additional feed, a photosynthetic cow would quickly starve to death if you stopped feeding it... (ignoring the still necessary mineral intake)
That’s not a fair comparison. This is generating ATP directly, rather extracting sugars and whatnot the plant, most of which is indigestible waste, so it’s not like you’d need the surface area of 14 kg of grass.
The real problem is that you need hemispherical hairless cows. ;)
ATP requires adenine and ribose. The former requires nitrogen fixed for the grass by microorganisms and the latter requires glucose for the pentose phosphate pathway. Adenine might also be recycled by the mitochondria which would further complicate things (can ATP be sent back into the mitochondria? Can the mitochondria recycle adenine without the entire glucose/electron transport pathway?)
I suspect a photosynthetic cow would still need to eat a lot of grass
> You process literal pounds of ADP to ATP and back to ADP, every day.
That's exactly my point. Some percentage of that ADP and ATP will be lost and the adenine/ribose broken down or reused for something else - cells are messy environments. Some of that will be lost permanently to waste. The more turnover in this process, the more opportunity for that loss.
> The real problem is that you need hemispherical hairless cows. ;)
That's a good opportunity to join forces with Sabine Hossenfelder and together move some of excess funding from, say, particle physics, and allocate it to fundamental research on which all physics depends: creation of frictionless, vacuum-rated spherical cows.
