Types of Autotrophs

Autotrophs can be grouped into two categories depending on the source of energy they utilize to produce their food.

1. Photoautotrophs

• Photoautotrophs are autotrophs that utilize solar energy and carbon dioxide to prepare their food by the process of photosynthesis.
• The photoautotrophs have a photosynthetic reaction center consisting of chlorophyll. The chlorophyll pigment is responsible for the transduction of radiation in cells.
• Photoautotrophs can be further divided into two groups based on the number of reaction centers in the photosynthetic apparatus and the ability to utilize water; oxygenic photoautotrophs and anoxygenic photoautotrophs.
• Oxygenic photoautotrophs utilize water as a source of reducing power in order to generate oxygen. Anoxygenic photoautotrophs depend on environmental reducing power in order to assimilate carbon dioxide.
• Photoautotrophs had been considered to be solely responsible for life on Earth; however, the idea has been challenged by the discovery of chemolithoautotrophs.
• Photoautotrophs include green plants and algae that contain chlorophyll. The chlorophyll is involved in capturing energy from sunlight which is utilized to assemble carbon dioxide into glucose.
• Green plants are producers of the terrestrial and aquatic ecosystems, which are consumed by heterotrophs known as consumers.
• The energy assembled by green plants is transferred to other animals through the food chain, which forms the basis of the ecosystem.
• Besides green plants, there are numerous photosynthetic bacteria that contain other photosynthetic pigments like rhodopsin, carotenoids, etc.
• Photoautotrophs are also important in the carbon cycle as these utilize carbon dioxide released by heterotrophs during respiration.

2. Chemoautotrophs

• Chemoautotrophs are autotrophs that utilize energy obtained from a chemical reaction involving oxidation in order to prepare their food.
• These differ from photoautotrophs in that they do not depend on sunlight for energy.
• The source of carbon, in the case of chemoautotrophs, is an oxidized form of carbon like carbon dioxide.
• The most well-known group of chemoautotrophs includes the chemolithoautotrophic that are found in rocks and utilize inorganic sources like ferrous ion, hydrogen, and hydrogen sulfide.
• These autotrophs are found in extreme habitats like deep-sea vents, acidic environments, and deep tranches.
• All chemoautotrophs are microorganisms belonging to the Archea and Bacteria domains. These have been studied intensely over the years to discover their role in the evolution of living beings on the planet.
• Chemoautotrophs are also studied for their role in astrobiology because of their ability to survive in extreme conditions.
• The energy used by these microorganisms is obtained from chemical reactions occurring in the environment. The energy is then transformed into cellular energy by the microorganisms.