AUTOTROPHIC ORGANISMS: CHARACTERISTICS AND EXAMPLES - BIOLOGY - 2025

The autotrophic organisms are living organisms that have the ability to produce their own food. That is, they can generate complex organic compounds, such as fats, carbohydrates or proteins, from simple elements. For this, they use inorganic chemical reactions or sunlight.

Examples of autotrophic organisms are plants, algae, and cyanobacteria. Thus, autotrophic organisms reduce carbon dioxide to generate organic compounds, which are used in the biosynthesis of substances. In addition, chemical energy is stored for use in different metabolisms.

Autotrophic organism, a tree. Source: pixabay.com.

The vast majority of autotrophs use water as a reducing agent, however, there are other organisms that use hydrogen sulfide. Likewise, considering the energy source used in the reactions, autotrophs are classified as photoautotrophs and chemoautotrophs.

Photoautotrophs, represented by plants, some bacteria, and green algae, use energy from sunlight. On the other hand, chemoautotrophs use sulfur or nitrogen as an energy source. Some archaea and bacteria, such as the sulfur bacteria, belong to this group.

Origin and evolution

There are various theories that try to explain the origin of life on earth. Along with these, scientists carry out research to find out how these ancestors obtained the energy to develop.

Some experts suggest that autotrophs, as they are currently known, possibly evolved secondary to the first living forms. The biochemical process that photosynthetic organisms use to produce their food is highly specialized.

This could suggest that such adaptations may have required a long time and successive evolutionary modifications. However, heterotrophs depend on autotrophs for food. Therefore, the proposals must revolve around the clarification of the doubts that arise in both cases.

First autotrophic cells

There is a theory that postulates autotrophic organisms as the first cells on Earth. According to these approaches, these structures satisfied their carbon needs from the CO2 found in the environment.

To explain the appearance of heterotrophs, the scientists who support this hypothesis suggest that the first chemoorganoheterotrophs developed on a substrate similar to that of Escherichia coli.

First heterotrophic cells

Another group of researchers support the idea that the first life forms were heterotrophic organisms, which later gave way to autotrophic beings.

According to some theories, the existing conditions on Earth favored the formation of amino acids and other basic compounds for the development of life. Based on this, the first heterotrophs were fed by these energy blocks.

However, the abundance of amino acid sources was decreasing. This exerted a strong evolutionary pressure on the heterotrophs, which caused the development and specialization of cells that were capable of producing their own food, through photosynthesis.

These new autotrophic beings initially depended on a variant of the photosynthetic process. Thus, they used hydrogen sulfide, which was later replaced by water, when the group of cyanobacteria intervened.

At the moment that water enters photosynthesis as a fundamental element, an important by-product is created: oxygen. This was excreted into the environment, where little by little its levels rose. Thus, a new variety of heterotrophic life probably evolved, those with the ability to breathe free oxygen.

Characteristics of autotrophic organisms

- ATP synthesis

Autotrophic organisms transform the energy that comes from the Sun into ATP bonds, through the process of photosynthesis. Much of this ATP is hydrolyzed in order to provide energy, which will be used in the conversion of carbon dioxide into six-carbon sugars.

- Products of photosynthesis

As the end product of photosynthesis, which occurs in chloroplasts, is sucrose, a disaccharide composed of fructose and glucose. This is transported to the tissues, which metabolize it for energy. Also, this process generates starch, which is a storage source of carbohydrates.

Likewise, photosynthesis releases oxygen into the environment. However, there are some bacteria, such as purple and green, where there is no oxygen production. In these a special type of solar energy process is carried out, known as anoxygenic photosynthesis.

- Producers

Plants are autotrophic organisms and they make their own food. Heterotrophic organisms feed on other organisms

Within the food chain, autotrophic organisms form the producer group. These are the basis of the diet of primary consumers, who, as herbivores, feed mainly on plant species.

-Energy transmission

Autotrophs convert and store energy into chemical bonds of simple sugars. These polymerize so they can be stored as long chain carbohydrates, including cellulose and starch. Glucose is also produced, and is the basis for proteins and fats.

When a heterotrophic organism ingests an autotrophic one, the fats, carbohydrates and proteins they contain allow the animal to carry out all its vital metabolic functions.

Types of autotrophic organisms

Photoautotrophs

Cyanobacteria genus Lyngbya filaments (oxygenic photosynthetic type bacteria)

Photoautotrophic organisms use light as an energy source to make organic matter. For this, they carry out the photosynthesis process. An example of these are plants, green algae, and some bacteria.

Chemoautotrophs

Chemoautotrophs are organisms that obtain energy from inorganic chemical processes. Currently, these organisms live deep, where they do not receive sunlight. Many live around volcanic vents, where heat facilitates metabolic reactions.

Examples of autotrophic organisms

- Plants and green algae

These are photoautotrophs, as they transform sunlight into reduced carbon, which acts as a source of chemical energy. Green algae and plants are fundamental in the food chain, since they are part of the group of primary producers.

- Iron bacteria

Iron bacteria are chemoautotrophs, since they receive energy from the oxidation of organic or inorganic substances. They generally inhabit the soil, in rivers, and in areas where iron is abundant, such as underground water sources.

- Sulfur bacteria

Sulfur bacteria are found in stagnant waters or sulfurous-type springs. Unlike green algae or plants, they do not use water as a reducing agent, therefore they do not produce oxygen.

Red sulfur bacteria are of great importance to the ecosystem, since they form an important part of the sulfur and carbon cycles. In addition, as primary producers, they are food for a wide range of aquatic organisms.

References

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