What is the difference between photosynthesis and chemosynthesis?

Photosynthesis, which forms the basis of food chains, involves the production of organic matter using energy from the sun. This is what plants do in the vegetable world and algae on the surface of the ocean.

The chemical reaction results from the combination of CO2 (carbon dioxide), water (H2O) and solar energy, which produces sugars and oxygen.

While photosynthesis uses the sun's energy, in the depths of the ocean where darkness reigns, the absence of light has long led to the belief that life could not develop there.

However, the discovery of hydrothermal vents in 1977 revealed the existence of an abundance of highly unusual animal life that could thrive in extreme conditions. 

How was this possible?

Deep down, around the hydrothermal vents, photosynthesis becomes chemosynthesis. Energy is no longer supplied by sunlight, but by the absorption of hydrogen sulphide molecules released by the hydrothermal vents. Bacteria feed on these molecules and transform them into organic matter, which is used as food by the animals living around the vents.

Photo : Ifremer