Question

Why is photosynthesis important for ecosystems everywhere

Answer 1

it allows plants to survive  and continue to  reproduce

Answer 2

Photosynthesis is literally the most important thing to the ecosystem, and in short is the source of all chemical energy (the kind the organisms use) in the ecosystem. ... This is why plants that perform photosynthesis are known as Producers, because they produce all of the original chemical energy in the ecosystem.