One reason photosynthesis receives such an honored title is that without it, multiple things would be gone that keep life going. Sure, it changes carbon dioxide into oxygen - as you know; but it also make many plants grow. This fends the land and makes more plants. And it feeds the animals that eat plants. Who eats those? Sure- everyone except carnivores. And carnivores eat those who eat plants. So, everything leads back to the Life-driving process... Now breath.