Algae are plant-like microorganisms that preceded plants in developing photosynthesis, the ability to turn sunlight into energy. Algae cells contain light-absorbing chloroplasts and produce oxygen through photosynthesis.
Although plants generally get the credit for producing the oxygen we breathe, some 75% or more of the oxygen in the planet’s atmosphere is actually produced by photosynthetic algae and cyanobacteria.
Algae also play an important role as the foundation for the aquatic food chain. All higher aquatic life forms depend either directly or indirectly on microscopic gardens of algae.
Most unicellular algae live in water, some dwell in moist soil, and others join with fungi to form lichens.
Algae are found in bodies of fresh and salt water across the globe. They can also grow on rocks and trees and in soil when enough moisture is available. (They also grow on the hair of the South American sloth, giving the animal a greenish color.)