Why we cannot make food ourselves by photosynthesis like plants do?

Humans have to grow, hunt, and gather food, but many living things aren’t so constrained. Plants, algae and many species of bacteria can make their own sustenance through the process of photosynthesis. They harness sunlight to drive the chemical reactions in their bodies that produce sugars.

Our body cells lack one cell organelle which is present in plants, that is, chloroplast. Chloroplast contains a pigment called chlorophyll which is necessary for the photosynthetic reactions to take place. Moreover, we inspire O₂ and expire CO₂ which is just opposite to that of plant. Then we cannot absorb water from soil neither we can absorb sunlight.

Chloroplasts are the structures, that we cannot just plug them into a fresh host cell and expect them to work normally, because many of the proteins that they use are encoded within the genome of their host cell. These proteins, which number in their hundreds, are made in the cell’s nucleus, and transported into the chloroplast.

“If we wanted to set up a relationship between a chloroplast and a new animal host, we need all that extra support machinery. You’d have to put those genes in the host’s genome.” And with hundreds of such genes, turning a human cell into a compatible home for chloroplasts would involve genetic engineering on a vast scale.

Hence, these are various reasons why we cannot photosynthesize like plants but depend upon them for food.