Plants and algae are photoautotrophs that gain their energy from sunlight, water, and gases in the air to create their own food. They draw water and minerals from the soil up through their roots. Then the plants absorb carbon dioxide in the air and release oxygen through tiny holes in their leaves, branches, and roots. This is a process called respiration. Sunlight gives chloroplasts energy to make glucose, which is their food source. Glucose is a sugar that is broken down by mitochondria into ATP, adenosine triphosphate, energy which the plant needs to connect carbon dioxide molecules together to form glucose.

The chemical formula for photosynthesis is 6CO2 + 6H2O + Light energy → C6H12O6 (sugar) + 6O2. Autotrophs are crucial for providing nutrition to all other forms of life.

In places where there is not enough sunlight for photosynthesis, chemoautotrophs thrive. Chemoautotrophs include bacteria and fungi that live in the soil, deep in the ocean, and around volcanoes in hydrothermal vents. Instead of using the sun as a source of energy, they turn inorganic compounds into energy. Chemoautotrophs are believed to be one of the earliest living organisms, so they had to adapt to living off the few chemicals that were present on Earth which included iron, nitrogen, sulfur, and magnesium.