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Autotrophs That Utilize Light As Their Energy Source

Autotrophs derive their name from the Greek words for "self" and "feeding." Autotrophic organisms use light and inorganic materials to make their own food in a process called photosynthesis. By contrast, heterotrophs can only use organic materials. They don't make their own food and rely on autotrophs, the primary producers in almost every food chain on the planet, to supply them with nutrients.

Photosynthesis
- Colorful phytoplankton produce half of the planet's oxygen.
  
  Photosynthesis -- the chemical process that uses energy from light to form compounds that store that energy in chemical form -- defines photoautotrophs. Autotrophic plankton, plants and bacteria scrub the air of carbon dioxide, and most produce oxygen as a byproduct of photosynthesis. These organisms stabilize the amounts of carbon dioxide and oxygen in Earth's atmosphere. Tiny phytoplankton produce half of the world's oxygen supply; these microscopic photosynthesizers not only feed the world, they give it breath.
Bacteria
- Blue-green bacteria are common autotrophs.
  
  Most photosynthetic bacteria fall into the phylum Cyanobacteria. They're some of the oldest organisms on Earth; fossilized remains of Cyanobacteria colonies are as much as three billion years old. These unicellular organisms have no differentiated nuclei and no cell walls, but grow into visible colonies colloquially called "blue-green algae." Cyanobacteria are considerably older than algae, though, and the two are not related directly. While purple sulfur bacteria also photosynthesize, they produce sulfur, not oxygen, as a byproduct of their photosynthetic reaction.
Algae
- Algae make up an underwater kelp forest.
  
  Algae are a diverse group of life forms that include both unicellular creatures and large multicellular organisms such as kelp. Although they're related to land plants, algae are simpler autotrophs; they lack specialized structures such as flowers, seeds and vascularization. All forms of algae require water to survive, but some types have developed strategies for harsh climates. Lichens, for example, are a symbiotic relationship between a fungus and an alga; the fungus shelters the alga as the alga provides energy to the fungus.
Plants
- Plants are autotrophs that turn sunlight into a wide variety of foods for land-based animals.
  
  Plants are the most familiar autotrophs, and include mosses, ferns, cycads, conifers and flowering plants. Plants have colonized every continent on the planet. They're the basis of almost all land-based animals' food, either directly or indirectly; the steak, the potato beside it and the wine served with it all originated with autotrophic plant life. Plants' need for light and water has shaped them for widely varied climates. Cacti have no leaves from which to lose precious moisture, while rainforest plants commonly have broad leaves to maximize the light they receive. Sequoias grow tall to reach for sunlight, while grasses spread rhizomes and form broad expanses to soak up the sun.

Nature