# human photosynthesis

Discussion in 'Biology & Genetics' started by ethernos, Sep 25, 2017.

1. ### ethernosRegistered Member

Messages:
87
are there scientist who would want to perform human experiments realated to photosynthesis ?

Messages:
10,676
No.

5. ### KittamaruAshes to ashes, dust to dust. Adieu, Sciforums.Valued Senior Member

Messages:
13,938
Well... there is a sea slug that does it (one of the only known animals to obtain energy via direct photosynthesis if memory serves)
http://blog.mbl.edu/2015/02/03/sea-...o-photosynthesize-like-a-plant-study-reports/

That said... plants run at about 3 to 6% efficiency when performing photosynthesis:

https://en.wikipedia.org/wiki/Photosynthetic_efficiency

By compare, a human is estimated to be around 20% efficient in terms of metabolic efficiency:
https://www.quora.com/How-efficient-is-the-human-body-at-converting-food-energy-into-work-energy

To take it further, and make a comparable figure, the human body needs about 80-100watts of energy just to keep itself alive (no physical activity, et al).
https://physics.stackexchange.com/questions/46788/how-efficient-is-the-human-body
A plant, on the other hand, averages at the maximum roughly .7 Watts per square meter:
https://en.wikipedia.org/wiki/Photosynthetic_efficiency#Efficiencies_of_various_biofuel_crops

So, if we made a person photosynthesize at the .7 Watts / m^2 maximum across the average human surface area:
http://www.medicinenet.com/script/main/art.asp?articlekey=39851
So, call it 2 square meters... that gives us 1.4 watts. That gives us roughly 98.6 watts to make up, just to stay alive.

Factor in clothing, shade cast by parts of the body casting shadow on other parts, places where the sun doesn't shine (unless you plan to stick a gro-lamp up your bum!), etc... and I think we can safely say that, even if we managed to up the efficiency of photosynthesis to current photovoltaic levels, which would give us about 44 watts, that a person simply could not produce enough energy via photosynthesis to survive... or, honestly, really make any difference in the amount of food they would have to eat to sustain themselves through even a mild jog.

7. ### YazataValued Senior Member

Messages:
5,021
Sure. Several have won Nobel Prizes for it.

http://ar.iiarjournals.org/content/36/3/1345.long

The human body synthesizes several important chemicals using energy from sunlight, most notably vitamin D.

What it doesn't do is synthesize sugars (food) like glucose C6H12O6 and long-chain polysaccharides like cellulose (plant body structural material) from CO2, H2O and light energy the way green plants do. (Plants actually feed themselves from water and air! Humans think that CO2 sucks, but plants love it.)

Last edited: Sep 25, 2017
ethernos likes this.
8. ### billvonValued Senior Member

Messages:
14,932
No one thinks CO2 sucks (with the possible exception of the handful of people who have been killed by CO2 asphyxiation, that is.) It has some pretty important uses. Like almost everything, there are some problems with it in large quantities, though.

ethernos likes this.
9. ### timojinValued Senior Member

Messages:
3,252

ethernos likes this.
10. ### KittamaruAshes to ashes, dust to dust. Adieu, Sciforums.Valued Senior Member

Messages:
13,938
... Come again?

Are you actually asking if my father penned that analysis?

11. ### DaveC426913Valued Senior Member

Messages:
10,781
Like regulating our breathing.

If CO2 in your system drops too low, your brain will tell your lungs to stop breathing.

ethernos likes this.
12. ### KittamaruAshes to ashes, dust to dust. Adieu, Sciforums.Valued Senior Member

Messages:
13,938
Which is why hyperventilating is so bad, if I'm not mistaken... And why the whole "breathing into a paper bag" thing came to be?

13. ### exchemistValued Senior Member

Messages:
7,715
And is also why oxygen starvation is NOT obvious. It does not make you gasp for air. What makes you gasp for air is excess CO2 in the blood.

In the 1980s a shift supervisor at Shell Haven refinery died by putting his head into a column that was being purged with nitrogen. Very foolish thing to do - and there was a big inquest into safety procedures of course. He would have got no feeling of asphyxiation to warn him, because his lungs would have been able to get rid of CO2 as normal.

When my wife was anaemic (due to chemotherapy) she became ill on the flight home from holiday: nauseous, light-headed, sweating, incontinent. It was oxygen starvation, due to the reduced cabin pressure at high altitude. But no gasping for air at all, just feeing lousy.

ethernos and DaveC426913 like this.
14. ### KittamaruAshes to ashes, dust to dust. Adieu, Sciforums.Valued Senior Member

Messages:
13,938
Still waiting for some sort of explanation as to what the deuce you meant here...

15. ### spidergoatVenued Serial MembershipValued Senior Member

Messages:
53,489
Not sure if people are aware, but it's possible to become infected with a form of algae. I knew someone with green patches on the skin, doctors said it probably wasn't a problem unless they spread.

ethernos likes this.
16. ### DaveC426913Valued Senior Member

Messages:
10,781
I find this highly implausible.

ethernos likes this.
17. ### river

Messages:
11,650

ethernos likes this.
18. ### ethernosRegistered Member

Messages:
87
hope she is well.....

19. ### ethernosRegistered Member

Messages:
87
if we could use our hair for photosynthesis that be interesting ....

Last edited: Oct 2, 2017
20. ### billvonValued Senior Member

Messages:
14,932
Hypoxia does indeed make you gasp for air. It's just not as obvious as hypercapnia.

21. ### KittamaruAshes to ashes, dust to dust. Adieu, Sciforums.Valued Senior Member

Messages:
13,938
Well, I mean, as the quick n dirty calculations I ran above point out... it would do nearly nothing in the face of our daily caloric burn.

22. ### ethernosRegistered Member

Messages:
87
if there were possibility of increasing the efficiency.

23. ### DaveC426913Valued Senior Member

Messages:
10,781
That would be a function of surface area.
Imagine a 150 pound plant, with maybe one square foot of leaf surface area. That's way too small even for a sessile plant!