Autotrophs are organisms that can convert inorganic materials into nutritive organic molecules. They use two different methods including photosynthesis (which involves light energy) and chemosynthesis (which involves chemical energy) to produce organic molecules.
Photoautotrophs are those organisms that synthesize food through the process of photosynthesis whereas chemoautotrophs synthesize food through chemosynthesis. Autotrophs are also known as autophytes. They produce their food hence they are called producers.
Etymology: The word autotroph is made of the Greek word autos, meaning “self” and trophe, meaning “nutrition.” Synonyms: autotrophic organism, primary producer
Types of Autotrophs
Autotrophs are classified into two major types:
The organisms that perform photosynthesis in the presence of sunlight are called photoautotrophs. They produce organic compounds, such as carbohydrates, fats, and proteins, from inorganic substances. The equation for photosynthesis is as follows:
6CO2 + 12H2O + energy ⇒ C6H12O6 + 6O2 + 6H2O
Photoautotrophs consist high amount of chlorophyll pigments that capture sunlight. The chlorophyll has found in specific organelles called the chloroplast. Chlorophyll is also responsible for the green color of leaves. Some other pigments are also used in the process of photosynthesis such as accessory pigments.
Accessory pigments include carotenoids and phycobilins help in absorbing light. The process needs inorganic substances such as carbon dioxide, inorganic salts, and water to perform photosynthesis in the presence of sunlight.
In the present scenario, several artificial light resources are also developed and proven useful in inciting photosynthesis. The research in lighting plays an important role in crop improvement and horticulture.
Several organisms produce their food by the process of chemosynthesis and do not require sunlight. These organisms are called chemoautotrophs. Instead of photoautotrophs, chemoautotrophs use chemical energy to produce organic molecules such as carbohydrates. They convert the inorganic compounds such as hydrogen sulfide, sulfur, ammonium into sugar molecules.
All the Green land plants, algae, and lichens are common examples of autotrophs. The land plants include grasses, dicots, gymnosperms, bryophytes, and ferns and photosynthetic algae such as charophytes, chlorophytes, dinoflagellates, and diatoms are examples of autotrophs.
They all contain chlorophyll that absorbs sunlight. Due to the high amount of chlorophyll plants have a distinctively green color especially in photosynthetic organs (e.g. leaves). They produce organic molecules and store food in form of starch.
Plants also produce oxygen as a by-product and release it into the air that is used by other organisms in the process of aerobic respiration. Examples of chemoautotrophs include methanogens, halophiles, nitrifiers, thermoacidophiles, and sulfur oxidizers.
The Role of Autotrophs in an Ecosystem
Autotrophs play many important roles in an ecosystem. They act as primary producers in a food chain and are found at the base of the ecological pyramid. They are autotrophic organisms that mean they produce their food and do not depend on other organisms whereas the heterotrophic organisms cannot make their food and rely on primary producers for nutrition.
Autotrophs store food in the form of starch that is an energy source for heterotrophic organisms. Autotrophs also perform in nutrient cycles of the ecosystem.
They can convert complex molecules into simpler substances, For example, carbon dioxide is used by plants to produce organic molecules through photosynthesis. They also produce oxygen as a by-product and release it into the environment through transpiration.
The oxygen is used by other aerobic organisms for aerobic respiration. All living organisms, especially animals use oxygen in the redox reaction during ATP synthesis. ATP is an energy currency for all animals that are used to perform metabolic activities or other cellular functions properly.
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- Carbohydrate movement from autotrophs to heterotrophs in parasitic and mutualistic symbiosis. Biol Rev Camb Philos Soc . 1969 Feb;44(1):17-90.