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Autotroph Definition
Autotroph comprise organisms that utilize inorganic substances to prepare their own food. The root words for the term “autotroph” include “auto” signifying self and “troph” which means food. These kinds of organisms do not rely on other organisms for their nourishment.
What is Autotroph?
An autotroph is an organism that can produce its own food using light, water, carbon dioxide, or other chemicals. Because autotrophs produce their own food, they are sometimes called producers.
The rest of the animals of other trophic levels are dependent on the autotrophs that are the producers that kick starts a food chain. Producers reduce inorganic carbon and fix it in an organic form like sugars, utilizing energy from sunlight. They are at the very base of the energy pyramid of an ecosystem as all other organisms (heterotrophs) are dependent on them.
Herbivores depend on them, and carnivores in turn depend on herbivores for their food. From this we can predict that producers must have been the first life-forms to exist on Earth, they evolved to synthesize organic food and make their energy from inorganic sources. Heterotrophs evolved later and may have become dependent on autotrophs since it is easier to ingest them than to synthesize their own food.
Types of Autotrophs
Based on their sources of energy autotrophs are further classified into chemoautotrophs and photoautotrophs.
i. Photoautotrophs
They depend on the sunlight to derive their energy from them to fuels the reactions required to fix carbon. This group includes bacteria, green algae, and plants all of which perform the process of photosynthesis. Photosynthesis is made of 2 root words, “light” and “to make”.
The energy from sunlight is captured in form of photons and then this energy is harvested for different biochemical processes for synthesizing ATP molecules. These photoautotrophs capture the Sun’s energy and store it in their molecular bonds and also synthesize sugars by fixing carbon.
Carbon dioxide in the surrounding is taken by the plant, while oxygen that is vital for organisms is released as a byproduct. It was the evolution of photoautotrophs that lead to the production of aerobic conditions by releasing oxygen. The enormous amount of oxygen produced caused the iron dissolved in the ocean to rust which led to the production of banded iron formations that are actually rocks.
This aerobic environment caused the evolution of other aerobic organisms that later thrived and evolved into different lineages. The oxygen released by photoautotrophs also contributed to the formation of the ozone layer that blocked harmful rays of Sun.
ii. Chemoautotrophs
They obtain their energy by utilizing chemical inorganic processes. They are naturally found in environments that receive no sunlight like deep waters. Certain chemoautotrophs are present near deep water volcanic vents that aid in the occurrence of metabolic reactions at a higher rate.
Their energy sources are usually volatile chemicals like hydrogen sulfide, molecular hydrogen, elemental sulfur, ammonia, and ferrous iron. They can survive in extremely toxic places due to this.
Archaebacteria and bacteria comprise chemoautotrophs, due to the limited efficiency of their metabolism they do not support multicellularity. There is also speculation that life may be possible by chemoautotrophic metabolism in the chemically volatile sites like in the seas of Jupiter’s moon Titan.
Chemoautotrophs raise the possibility of existence and life beyond the earth, but no proof of this has been found yet. It is difficult to ascertain which kind of autotrophs existed first on Earth. Some scientists believe that it was photoautotrophs who evolved first since in the primordial Earth there was sunlight available bountifully to all surfaces.
Chemoautotrophs were believed to evolved near volcanic sites in deep seas where volatile chemicals were concentrated. Some hypothesize that photoautotrophs could have evolved from these cells as they spread to Earth’s surface and evolved photosynthesis. Due to a lack of fossil evidence, it is difficult to ascertain which life form existed first.
Autotrophs Examples
i. Plants
Almost all plants, except some carnivorous plants like venus fly trap, are photoautotrophs. They utilize green pigments chlorophyll that has photosystems to capture energy from sunlight and have the required enzymes to reduce inorganic carbon to synthesize sugars. Heterotrophs mainly comprising of animals depend on them for organic materials.
ii. Green Algae
They are also known as pond scum that are photoautotrophs that do resemble green bacteria cyanobacteria. Cyanobacteria were some of the earliest life forms to have evolved on Earth that also produced an aerobic atmosphere.
”Iron Bacteria” – Acidithiobacillus ferrooxidans
They derive their energy from ferrous iron by converting the molecular form of iron to a form that can be dissolved in water. They have been used recently for this purpose to extract iron from ores.
Autotroph Citations
- Nutrient recycling affects autotroph and ecosystem stoichiometry. Am Nat . 2008 Apr;171(4):511-23.
- What is an autotroph? Arch Microbiol . 2012 Feb;194(2):135-40.
- Predominant Non-additive Effects of Multiple Stressors on Autotroph C:N:P Ratios Propagate in Freshwater and Marine Food Webs. Front Microbiol . 2018 Jan 30;9:69.
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