Autotroph Vs Heterotroph: The Difference

Squirrel (heterotroph) eating a plant (autotroph)

The difference between an autotroph vs. heterotroph lies in the organism’s ability either produce its own food or need to ingest food. Autotrophs, such as plants, can produce their own food from light via photosynthesis or chemicals via chemosynthesis. Heterotrophs, such as humans, require ingesting food in order to produce energy and thus are not self-sustaining as plants are.

Organisms come in all shapes and sizes and scientists use different labels to make sense of the diversity that exists. Humans are referred to as Homo sapiens because that is our taxonomic name, which is important to classify and differentiate the many different species that exist.

A chicken (Gallus gallus domesticus) is taxonomically different, among other differences, so it has a different taxonomic name to indicate that, among many other pieces of information. Other labels include things like diet, which includes omnivores, carnivores, and herbivores. These labels are used to also inform us about organisms habitats, behaviors, morphology, and many other factors that aid us in creating an accurate picture of a species. Two big labels that encompass life on Earth are heterotrophs and autotrophs. These are two mechanisms of nutrition that organisms use to gain their adequate nutrition to survive. While they do not capture every nutritional information about an organism, they are helpful starting points to inform us about an organism’s behavior.

The subgroups of autotrophs and heterotrophs. Image from Wikipedia

Heterotrophs

Heterotrophs are organisms that are incapable of creating their own nutrients and must rely on other organisms to fulfill that need. These include all animals and fungi as well as some bacteria and protists, which are eukaryotes that are neither animals or fungi. This accounts for 95% of living organisms and can be further broken down based on what their food source is.

There are chemoheterotrophs, which gets their energy from organic compounds, like plants or other living matter. There are also photoheterotrophs, which uses sunlight to get their energy from things like fatty acids, carbohydrates, and other carbon compounds excluding carbon dioxide. Since heterotrophs rely on the consumption of other organisms, they are usually at the top or above autotrophs in the food chain and transfer of energy. The energy that is obtained is used for things like growth and reproduction. Animals get their energy from ingestion while fungi get theirs through absorption. Bacteria employ a variety of tactics to get their energy.

Heterotrophic Animals And Fungi

A well-known heterotroph is humans. Humans ingest their food source and it breaks up into smaller pieces, which is facilitated by enzymes. As they break into smaller pieces, they are absorbed in the intestines and into the body. The body sends the nutrients to where they need to go and anything not used is stored as fat or removed.

This applies to many other animals, like lions, tigers, and bears. Humans are omnivores and capable of consuming almost anything organic that is not harmful to us. The differences between omnivores, carnivores, and herbivores include changes in digestive enzymes, gut bacteria, teeth composition, and even stomach acid. Despite these many differences, the process generally boils down to the breakdown of food that becomes the basic nutrients needed to sustain the body.

Fungi are part of a group called detritivores, which are responsible for the decomposition of dead organic matter. They break down dead plants, trees, and animals. Again, they use specialized enzymes to break down the food source of their choice to absorb the nutrients. Detritivores play the important role of continuing the cycle of organic to inorganic and back to organic because that continues to fuel the organisms that inhabit the earth.

Autotrophs

Autotrophs are organisms that must create their own organic compounds, like fatty acids or carbohydrates, using light or inorganic chemical reactions. Autotrophs include plants, algae, and some bacteria. They are considered producers because they create complex organic compounds and they do not need to consume another living organism to survive. Autotrophs can be broken into two main groups: photosynthesis, using light, and chemosynthesis, using chemical reactions.

Photosynthesis uses carbon dioxide and water, which can change depending on the specific autotroph, along with a light source to create glucose. Glucose, a sugar, is used to supply the photosynthetic organism with energy. Some organisms use things like hydrogen sulfide instead of water. In chemosynthesis, organisms use something like hydrogen sulfide or methane to turn carbon compounds, like carbon dioxide, into organic compounds. These are usually bacteria. Because they are producers of energy containing compounds, they are usually at the bottom of the food chain and supply food to everything above, which are usually the heterotrophs.

Chemoautotrophs in Hostile Environments

Bacteria and archaea that live in extreme environments are usually using chemosynthesis to produce and fulfill their energy needs because they lack things like sunlight.

Hydrogen Sulfide Chemosynthesis

12H2S + 6CO2 → C6H12O6 (=carbohydrate) + 6H2O + 12S

Some species include things like methanogens, which uses carbon dioxide with hydrogen to create methane and water byproduct. The methane serves as the organic compound for energy. There are also halophiles, which exist in high saline environments, thermophiles, acidophile, and many other groups for hostile environments.

Photoautotrophs All Around Us

There numerous plants and trees all over the planet and every one of them uses photosynthesis to create glucose. Glucose is used to create energy, but it is also used to create cellulose, which they use to build their cell walls and make themselves stronger.

This process supplies oxygen to the Earth and helps cleans the air, making it a crucial part of the world we live in. Plants also serve as an important diet for humans, a heterotroph. Besides plants, there are also cyanobacteria that use photosynthesis to create energy. These organisms are important because helped to create the world as it is today.

The cycle that connects autotrophs and heterotrophs as compounds move and change. Image from Wikipedia

Autotrophs and heterotrophs give a partial picture of a species existence because both are dependent on other organisms for survival beyond nutrients. Other organisms can provide needed things like phosphorous or nitrogen. There are some heterotrophs and autotrophs that have formed symbiotic relationships because of this necessity.

It is because of these complexities that breaking down organisms into different, sometimes intermingling, groups provides us with crucial information on biology, ecology, and even evolution. They also help us to understand ourselves and the roles our ancestors played as they interacted with their environment.

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