AUTOTROPHIC NUTRITION: CHARACTERISTICS, STAGES, TYPES, EXAMPLES - BIOLOGY - 2025

The autotrophic nutrition is a process that occurs in autotrophic organisms, where, from inorganic substances, the necessary compounds are produced for maintenance and development of these living beings. In this case, the energy comes from sunlight or some chemical compounds.

For example, plants and algae are autotrophic organisms, since they produce their own energy; they do not need to feed on other living beings. In contrast, herbivorous, omnivorous or carnivorous animals are heterotrophs.

Autotrophic nutrition. Source: pixabay.com

Taking into consideration the type of source used in the nutrition procedure, there are photoautotrophic and chemoautotrophic organisms. The former obtain their energy from sunlight and are represented by plants, algae and some photosynthetic bacteria.

On the other hand, chemoautotrophs use various reduced inorganic compounds, such as molecular hydrogen, to perform the procedures that allow them to obtain their nutrients. This group is made up of bacteria.

characteristics

- Energy conversion

The first principle of thermodynamics states that energy is neither destroyed nor created. It undergoes transformations in other types of energy, different from the original source. In this sense, in autotrophic nutrition, chemical and solar energy is converted into various by-products, such as glucose.

- Energy transfer

Autotrophic nutrition is typical of autotrophic beings, who form the basis of all food chains. In this sense, the energy is transferred from the autotrophs to the primary consumers that consume them and then to the carnivores that devour the primary ones.

Thus, a plant, as an autotrophic or producer organism, is the main food of the deer (primary consumer) and the mountain lion (secondary consumer), it hunts and consumes the deer. When the lion dies, microorganisms and bacteria act on the decomposed matter, and the energy returns to the earth again.

In hydrothermal vents, autotrophic bacteria are the producing organism of the food web. Mussels and snails are the primary consumers, feeding on bacteria. In turn, the octopus includes these mollusks in its diet.

- Specialized structures and substances

Chloroplasts

Chloroplast

Chloroplasts are oval organelles found in the cells of plants and algae. They are surrounded by membranes and the photosynthesis process occurs inside them.

The two membranous tissues that surround them have a continuous structure, which delimit them. The outer layer is permeable, due to the presence of porins. As for the inner membrane, it contains proteins, which are responsible for the transport of substances.

Inside it has a cavity, known as a stroma. There are ribosomes, lipids, starch granules, and circular double-stranded DNA. In addition, they have saccules called thylakoids, whose membranes contain photosynthetic pigments, lipids, enzymes and proteins.

Photosynthetic pigments

These pigments absorb the energy from sunlight, to be processed by the photosynthetic system.

Chlorophyll

Chlorophyll

Chlorophyll is a green pigment that is made up of a ring of a chromoprotein called porphyrin. Around it, electrons migrate freely, causing the ring to have the potential to gain or lose electrons.

Because of this, it has the potential to provide electrons that are energized to other molecules. Thus, solar energy is captured and transmitted to other photosynthetic structures.

There are several types of chlorophyll. Chlorophyll a is in plants and algae. Type b is found in plants and green algae. On the other hand, chlorophyll c is present in dinoflagellates and type d, is possessed by cyanobacteria.

Carotenoids

Like other photosynthetic pigments, carotenoids capture light energy. However, in addition to this, they contribute to dissipating excess absorbed radiation.

Carotenoids lack the ability to directly use light energy for photosynthesis. These transfer the absorbed energy to the chlorophyll, which is why they are considered accessory pigments.

Extreme environments

Tardigrades, a Phylum known for its ability to survive in very rough environments. Source: Willow Gabriel, Goldstein Lab, via Wikimedia Commons

Many chemoautotrophs, including nitrifying bacteria, are distributed in lakes, seas, and on the ground. However, some others tend to live in some unusual ecosystems, where there are the chemicals necessary to carry out oxidation.

For example, the bacteria that live in active volcanoes oxidize sulfur to make their food. Also, in Yellowstone National Park, in the United States, there are bacteria that are located in hot springs. Also, some live deep in the ocean, close to hydrothermal vents.

In this area, water seeps through a crevice in the hot rocks. This causes various minerals to be incorporated into seawater, among which is hydrogen sulfide, which is used by bacteria for chemosynthesis.

Stages of autotrophic nutrition

In general, autotrophic nutrition develops in three phases. These are:

The membrane passage and energy capture

In this process, reduced inorganic molecules, such as ammonia, and simple inorganic molecules, such as salts, water, and carbon dioxide, pass through the semi-permeable cell membrane, without causing the cell to waste energy.

On the other hand, in photoautotrophic organisms the capture of light energy occurs, which is the source used to carry out the photosynthesis process.

Metabolism

During autotrophic nutrition, a set of chemical reactions occur in the cell cytoplasm. As a result of these processes, the biochemical energy is obtained that will be used by the cell to carry out its vital functions.

Excretion

This final phase consists of the elimination, through the semi-permeable cell membrane, of all waste products that come from nutritional metabolism.

Types

Taking into consideration the type of energy source used, autotrophic nutrition is classified in two ways, photoautotrophic and chemoautotrophic.

Photoautotrophs

Photoautotrophs are organisms that obtain the energy to make organic compounds from sunlight, a process called photosynthesis. Green algae, plants and some photosynthetic bacteria belong to this group.

Photosynthesis occurs in chloroplasts and has two phases. The first is the light one. In this, there is a dissociation of the water molecule, for which light energy is used. The product of this phase are ATP and NADPH molecules.

This chemical energy is used in the second stage of the process, known as the dark phase. This occurs in the stroma of chloroplasts and receives that name because it does not require light energy for chemical processes to take place.

NADPH and ATP, product of the light phase, are used to synthesize organic matter, such as glucose, using carbon dioxide, sulfates and nitrites and nitrates as a source of nitrogen.

Chemoautotrophs

Nitrobacter is a genus of chemotrophic bacteria

Chemoautotrophic organisms, represented by bacteria, are capable of employing reduced inorganic compounds as the basis for respiratory metabolism.

In the same way as photoautotrophs, this group uses carbon dioxide (CO2) as the main source of carbon, being assimilated in the same way, by the reactions of the Calvin cycle. However, unlike these, chemoautotrophs do not use sunlight as a source of energy.

The energy they require is the product of the oxidation of some reduced inorganic compounds, such as molecular hydrogen, ferrous iron, hydrogen sulfide, ammonia, and various reduced forms of sulfur (H2S, S, S2O3-).

Currently, chemoautotrophs are commonly found in deep water, where sunlight is almost zero. Many of these organisms need to live around volcanic vents. In this way the environment is warm enough for the metabolic process to occur at a high rate.

Examples of living things with autotrophic nutrition

The plants

With few exceptions, such as the Venus flytrap (Dionaea muscipula) which can trap insects and digest them by enzymatic action, all plants are exclusively autotrophic.

Green algae

Green algae are a paraphyletic group of algae, which are closely related to land plants. There are currently more than 10,000 different species. They generally live in various freshwater habitats, although they could be found in some seas on the planet.

This group has pigments such as chlorophyll a and b, xanthophylls, β-carotene and some reserve substances, such as starch.

Examples:

- Ulva lactuca, known as lamilla, is a green algae that grows in the intertidal zone of the vast majority of the oceans. It has particular long leaves, with curled edges, which give it a lettuce appearance.

This species is within the group of edible algae. In addition, it is used in the cosmetic industry, in the production of moisturizing products.

- Volvox aureus lives in fresh water, forming spherical colonies of approximately 0.5 millimeters. These clusters are made up of around 300 to 3200 cells, which are interconnected by plasma fibers. Starch is accumulated in chloroplasts and they have photosynthetic pigments such as chlorophyll a, b, and ß-carotene.

Cyanobacteria

Cyanobacteria were formerly known by the names of chloroxybacteria, blue-green algae and blue-green algae. This is because it has chlorophyll pigments, which give it that green hue. Also, they have a morphology similar to algae.

These are a phylum of bacteria, made up of the only prokaryotes with the ability to use sunlight as energy and water as a source of electrons for photosynthesis.

Iron bacteria (

The bacteria Acidithiobacillus ferrooxidans get energy from ferrous iron. In this process, the insoluble iron atoms in water are converted into a soluble molecular form in water. This has allowed this species to be used to extract iron from some minerals, where they could not be removed in a conventional way.

Colorless sulfur bacteria

These bacteria transform hydrogen sulfide, a product of the decomposition of organic matter, into sulfate. This compound is used by plants.

References

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