Hello steemians !
Imagine the world where Human can prepare their own food inside their cells via photosynthesis. Imagine , There is no need tospend much time in cooking foods. Imagine , Just exposure to sunlight for half an hour will fill up your hunger. Isn't this seems cool to you? You can save much of your time and will not need much money to buy foods. And Yes , most importantly Human will not die of starvation.
This idea seems fascinating. A photosynthetic man is a dream project.

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Before knowing how photosynthesis works in human it is important to know the structure involved in photosynthesis.
Chloroplast is the main structure that is involved in photosynthesis.Beside it, Mitochondria also plays some role.

WHAT IS CHLOROPLAST?

Chloroplast is a plant cell organelle. It contains a green pigment called chlorophyll. Chlorophyll helps to absorb light that helps in photosynthesis.
In photosynthesis , solar energy is converted into chemical energy which is stored in the form of sugar. Carbondioxide, water and light is needed to make glucose, oxygen and water.

Figure:-chloroplast

The reaction of photosynthesis can be written as:-

6 CO2(g) + 12 H2O(l) + light → C6H12O6(aq) + 6 O2(g) + 6 H2O(l)

IS PHOTOSYNTHETIC ANIMAL POSSIBLE?

Yes, it is possible . The most important thing is to have chloroplast inside the animal cell.So, presence of chloroplast can start photosynthesis in animal. There is plenty of evidences that animal can synthesize food. Here , i will exlpain about two photosynthetic animals-one invertebrate and other vertebrate.

1.Sea Slug - Elysia chlorotica
It is a molluscan .Sea slug eats algae (that contains chloroplast ).These are taken up by phagocytosis in digestive tract. Chloroplast are then incorporated into cells. Reseschers have also found that sea slug also takes photosynthetic gene by lateral gene transfer ( a proceses in which gene is transferred between organism). Due to this reason they can prepare their own food.

Figure:-Elysia chlorotica
Sea slug can survive up to nine months without eating.

2.Spotted Salamander- Ambystoma maculatum
It is the first vertibrate that synthesize their own food.It maintains the symbiotic relationship with algal cells. Chloroplast cells are found inside salamander's cells. This helps them to synthesize food.

Figure:-spotted salamander

So, Is Photosynthetic Human possible ?

Theoretically speaking it is possible. It looks simple- implanting chloroplast in human cells can theoretically and practically leads to photosynthesis. The most difficult portion is to implant chloroplast. Just implanting one hundred to thousand chloroplast inside human cells is not going to work. A giant human body ( compared to salamander) needs more energy. The energy expenditure is even high during walking or performing other daily activities.

An average human skin has surface area of 1.8m2 and half of which would be expossed to sun. Solar radiation of wavelength 400-700nm is considered useful for photosynthesis( called photosynthetically active radiation or PAR). The amount of PAR light energy per unit area per second (Called PAR energy flux density ) is 400W/m2. Photosynthetic efficiency is 5%.

So, energy produced by human body by photosynthesis in an hour would be
400 x (1/2 x 1.8) x 5/100 x 3600 = 64800J = 64.8kj
An apple has 400kJ of energy. Now, you can imagine how much less energy is actually produced by photosynthesis.

[This single piece of apple will give more energy than one hour exposure to sun]

So, practically photosynthesis can occur in human body too but the energy produced by photosynthesis is not sufficient enough to meet the demand.

So, what problem can occur during and after the process ?

The Human body has complex and the advanced immune mechanism. It can easily reject implanted chloroplast. To prevent this we need high doses of immune suppressant. A suppressed immunity leads to high risk of infection and finally to death.

Exposure of a body part to the sunlight may lead to different types of cancer.

And most importantly our skin would be green ( as the color of chlorophyll). This is not a cosmetically a good idea. But with time we all become used to it.

At Last,

Though, it is possible to create photosynthetic man it would not be easy to reduce death due to starvation . There is more harmful aspect than benefit. Even a photosynthetic man would need to eat food for the survival. And more importantly , body will need more water ( for photosynthesis). But, after all, this seems fascinating idea.

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1.source 1
2.source 2
3.source 3
4.source 4

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Thanks for reading . Any feedback and comments are highly welcome !
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