What is the significance of photosynthesis on earth? Why would the biosphere be impossible without phototrophic organisms?

Photosynthesis is the only process on Earth in which the light energy of the sun is able to bind and conserve in the chemical bonds of the formed primary organic substance, which in turn can be used by herbivorous animals and protists as a direct source of food or, through intermediates, by predatory animals. Therefore, the formation of all types of food material is directly or indirectly associated with the activity of photoautotrophic organisms, determined by their ability to photosynthesis. As is known, free oxygen is a by-product of the light phase of photosynthesis. It saturates all the environments where phototrophic organisms live: atmospheric air, hydrosphere, soil, where atmospheric air penetrates. Without oxygen, the life of aerobic organisms, including humans, is impossible.

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