The main purpose of photosynthesis is to convert light energy from the Sun into chemical energy stored in sugars, providing food and fuel for the plant and, indirectly, for almost all other living things.

What photosynthesis does

  • Photosynthesis allows green plants, algae, and some bacteria to make their own food (like glucose) from carbon dioxide and water using sunlight.
  • In doing this, they store solar energy in chemical bonds, which organisms later use for growth, movement, and other life processes.
  • Oxygen is released as a by‑product, creating much of the breathable air on Earth.

Why it matters for life on Earth

  • Photosynthetic organisms sit at the base of almost every food chain, feeding herbivores, which then feed predators.
  • Nearly all the oxygen in the atmosphere comes from photosynthesis, so if it stopped, oxygen levels would eventually fall and most aerobic life would disappear.

TL;DR: The main purpose of photosynthesis is to turn sunlight into stored chemical energy (sugars), while producing oxygen that supports most life on Earth.