Analysis. Please explain why "nearly 90% of the oxygen on the earth is provided by algae".

A: Most algae live in water, a few live on land, and more than 70% of the earth is ocean. Therefore, algae plants in nature are abundant and widely distributed. Algae plants are simple in structure, with no differentiation in roots, stems and leaves, and chloroplasts in cells. The whole body can carry out photosynthesis and release oxygen. 90% of oxygen in nature is produced by algae, so algae is an important source of oxygen in the air.