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Autotrophs and heterotrophs – What are the difference?
Autotrophs and heterotrophs are two nutritional groups found in ecosystems. The main difference between autotrophs and heterotrophs is that autotrophs can produce their own food whereas heterotrophs eat other organisms as food.
| Autotrophs | Heterotrophs |
| “Self-feeders” – produce their own food | “Other eaters” – do not produce their own food |
| Make food from inorganic materials | Get food by eating other organisms |
| Producers | Consumers |
| At the primary level in a food chain | At the secondary and tertiary levels in a food chain |
| Are either photoautotrophs or chemoautotrophs | Are either herbivores, carnivores, omnivores, or detritivores |
| Plants, algae, some bacteria, and archaea | Animals, fungi, some bacteria, protists, and parasitic plants |
What is an Autotroph?
Autotrophs are organisms that are capable of producing their own nutrients using inorganic substances. What autotrophs need could be just the sunlight, water, carbon dioxide, or other chemicals. In contrast, heterotrophs are organisms that cannot produce their own nutrients and require the consumption of other organisms to live.
Autotrophs are the essential foundation of any ecosystem. They produce nutrients that are necessary for all other types of life on the planet. Because autotrophs produce their own food, they are also referred to as producers in food chains.
[In this image] In this pond ecosystem, algae as autotrophs are the producers that sustain all other heterotroph organisms. An increase in the number of autotrophs could supply the growth of heterotrophs, whereas the decrease in autotrophs results in starvation and a reduction in the number of other organisms as well.
[In this image] Have you seen the movie “The Martian” by Matt Damon in 2015? He planted a small farm of potatoes in order to survive on Mars. You can say that the potato plants are the producers for that extremely isolated ecosystem, and Matt is the consumer. Watch the movie here https://www.youtube.com/watch?v=TeZDLAaDYos
The name “autotroph” came from two words – “auto” means self and “-troph” means food, indicating that these organisms can produce their own food. The term “autotrophy” is often used to refer to the living strategy of autotroph organisms.
How does an Autotroph produce its own food?
Depending on the type of autotrophs, they either obtain the source of energy from sunlight or from chemical reactions.
Photoautotrophs
Plants are the most common types of autotrophs, and they use photosynthesis to convert solar energy to the nutrients that biological cells can use. This ktype of autotrophs is called photoautotrophs.
Plants have specialized organelles within their cells, called chloroplasts, which manage the process of photosynthesis. A group of pigment molecules called chlorophyll is responsible for the energy conversion in chloroplasts.
Learn more about chloroplasts by clicking the image below.
In combination with water and carbon dioxide, chloroplasts produce glucose, a simple sugar used for energy, as well as oxygen as a byproduct. Glucose provides nutrition for the plant cells. Glucose can also be transformed into other forms, such as starch that are stored for later usage or cellulose that is used to build the cell walls. Heterotrophs consume these plants to acquire this organic nutrition.
[In this image] Illustration of photosynthesis.
Chlorophylls in the chloroplasts absorb the solar energy and transfer the energy to ATP and NADPH. In the dark reaction, the enzymes and proteins in the chloroplasts use these high energy molecules to convert carbon dioxide to sugars.
Other examples of photoautotrophs include algae, phytoplankton, and some types of bacteria. However, some of them don’t have chloroplasts and may use other photosynthetic pigments to absorb sunlight. See later for these examples.
[In this image] Carbon Cycle.
Photoautotrophs are important in the carbon cycle as they utilize carbon dioxide released by heterotrophs during respiration to renew the energy source.
Photo credit: Sciencefacts.net
Chemoautotrophs
Some bacteria and archaea can utilize energy obtained from an oxidative chemical reaction (chemosynthesis). These chemoautotrophs differ from photoautotrophs in that they do not depend on sunlight for energy. Instead, chemoautotrophs use chemicals such as methane or hydrogen sulfide along with oxygen to produce carbon dioxide and energy. As a result, these chemoautotrophs are often found in extreme environments, like deep-sea vents, hot springs, and deep trenches.
Scientists believe that some chemoautotrophic archaea are closest to the earliest life forms on Earth. Chemoautotrophs are also studied for their role in astrobiology because of their ability to survive in extreme conditions.
[In this image] A comparison between the marine habitations suitable for photosynthesis and chemosynthesis.
Photo credit: Grid
Examples of Autotrophs
Green plants
Green plants are the most well-known group of autotrophs. Using water from the soil, carbon dioxide from the air and light from the Sun, green plants perform photosynthesis to provide their own nutrients (so they are photoautotrophs). Green plants are found in most ecosystems where they are the primary producers of food and energy for all other living organisms.
[In this image] Plants (the kingdom of Plantae), including liverworts, hornworts, mosses, ferns, conifers, and flowering plants, all live as photoautotrophs.
Algae
Algae (singular, alga) are a general term for a diverse group of eukaryotic organisms that are capable of photosynthesis. Algae include unicellular microalgae, such as the diatoms and chlorella, and multicellular algae, such as seaweeds that may reach 60 m in length and form underwater kelp forests.
Algae have chloroplasts, but their chloroplasts are different from the ones in land plants in terms of the number of chloroplasts in a cell, the shape of chloroplast, and the type of chlorophylls in chloroplasts. For example, volvox cells have only one giant, horseshoe-shaped chloroplast per cell.
Learn more about volvox by clicking the image below.
Green algae use chlorophylls primarily for photosynthesis. Red algae have chlorophylls but also have abundant amounts of phycobilins (a group of red pigments that also absorb sunlight) in their chloroplasts, giving red algae their distinctive color.
Learn more about green algae and red algae by clicking the images below.
Cyanobacteria
Cyanobacteria, also known as “blue-green algae,” are a group of free-living photosynthetic bacteria. Cyanobacteria are autotrophic and can obtain their energy through photosynthesis. Since cyanobacteria are prokaryotic cells, so of course, they do not have chloroplasts. Their chlorophyll molecules are in the cytosol.
Scientists believe that cyanobacteria played a significant role in Earth’s history by producing the largest source of O2 in the atmosphere today. However, an overgrowth of cyanobacteria called cyanobacteria bloom is harmful.
[In this figure] Left: Microscopic images of Cyanobacteria, showing many single cells assembled into long chains. Right: A picture of the cyanobacteria bloom.
Photo source: cyanobacteria, Beachapedia
Phytoplankton
Planktons are microorganisms that drift about in the water. Some planktons that display a plant-like behavior (meaning, can live by photosynthesis) are called phytoplankton. Phytoplankton can be divided into two classes – microalgae and cyanobacteria. Most freshwater phytoplankton are green algae and cyanobacteria. Marine phytoplankton are mainly comprised of microalgae known as dinoflagellates and diatoms.
Learn more about pond life microorganisms by clicking the images below.
Bacteria and archaea
Both bacteria and archaea are prokaryotic cells. Some of them can live by chemosynthesis in extreme environments.
For example, some bacteria near hydrothermal vents in the deep ocean can produce food using hydrogen sulfide. Hydrothermal vents are like geysers or hot springs on the ocean floor. Hydrothermal vents are commonly found near volcanically active places, where seawater seeps down through a narrow crack into hot, partly melted rock below.
The boiling-hot water then circulates back up into the ocean, loaded with minerals from the hot rock. These minerals, including hydrogen sulfide, are toxic to most organisms but could be used by certain bacteria to flourish.
[In this image] Hydrothermal vents form at locations where seawater meets magma.
Photo credit: National Ocean Service
These deep-sea vents could form unique ecosystems that don’t rely on solar energy at all. For example, scientists found colorless, ghost-like octopuses, tubeworms, sea stars, and yeti crabs feeding on bacteria that live off minerals spewed from the hydrothermal vents.
[In this video] Yeti crab (white) piles around the hydrothermal vents in Antarctica. These yeti crabs seem to cultivate “gardens” of bacteria on their chests, which are covered with hairy tendrils.
[In this image] Thermophilic archaea live in the mud volcanos of Yellowstone National Park.
Thermophilic archaea convert sulfur into sulfuric acid, which helps dissolve the rocks into mud. By living in such a superhot, acidic environment, they are the most extreme of all extremophiles on Earth.
Photo credit: National Park Service
Chemoautotroph bacteria can also be found at places called cold seeps. A cold seep, also known as a cold vent (compared to hydrothermal vents), is a shallow area in the ocean floor where the leaking of hydrocarbon-rich fluid, especially methane and hydrogen sulfide, occurs. Some bacteria, like Methanogens, live here by oxidizing these chemicals to produce energy.
[In this image] A bubbling cold seep.
Photo credit: WorldAtlas
What is a Heterotroph?
Heterotrophs are organisms that eat other plants or animals for energy and nutrients. The term came from the Greek words: “hetero” for “other” and “-troph” for nourishment. In an ecosystem, heterotrophs play the roles of consumers.
Examples of Heterotrophs
Heterotrophs include all animals and fungi, some bacteria and protists, and parasitic plants.
Heterotrophs occupy the second and third levels in a food chain. Herbivores – organisms that eat plants – occupy the second level. Carnivores (organisms that eat meat) and omnivores (organisms that eat both plants and meat) occupy the third level.
[In this image] A food chain shows how energy and matter flow from producers to consumers.
Photo credit: Biology LibreTexts
Detritivores or decomposers are also heterotrophic consumers. These organisms obtain food by feeding on the remains of plants and animals as well as fecal matter. Detritivores play an important role in maintaining a healthy ecosystem by recycling waste. Examples of detritivores include fungi, worms, and insects.
[In this image] Based on their relationship in a food chain, heterotrophs can be further classified as herbivores, carnivores, omnivores, and detritivores.
Mixotrophs – the gray area in-between autotrophs and heterotrophs
Could an organism be autotrophs and heterotrophs at the same time? Yes, many organisms possess the privilege to have more than one energy source. We call them – mixotrophs.
Carnivorous and parasitic plants
Among plants, carnivorous plants, such as venus flytrap, tropical pitcher plants, and sundews, can derive some nutrients from trapping and consuming insects. At the same time, they still keep the ability to generate energy from photosynthesis. Some semi-parasitic plants, like mistletoe and dodder, are also mixotrophs.
[In this image] Examples of carnivorous plants.
Symbiotic relationships
Many protozoans can live as mixotrophs by forming a symbiotic relationship with green algae. For example, symbiotic green algae can be found in species of stentors, paramecia, and amoebas.
[In this image] Stentor polymorphus with algal symbionts (Chlorella) living inside its body.
Stentor provides a safe place for green algae. In return, green algae provide foods for Stentor. Green algae can also absorb and feed on the Stentor’s metabolic wastes.
Photo credit: Mikro-Foto
Can animals live like plants?
Mixotrophy is less common among animals. There are some examples living in coral reefs. Several members of cnidarians (e.g., coral, jellyfish, and sea anemones) host endosymbiotic microalgae within their cells, thus making them mixotrophs.
[In this image] These sea anemones have beautiful green color due to symbiotic algae living inside.
This symbiotic relationship between algae and sea anemones is beneficial to both. The sea anemones get oxygen and nutrients, whereas the algae get protection.
Elysia chlorotica (common name is the eastern emerald elysia) is one of the “solar-powered sea slugs”, utilizing solar energy like plants to generate energy. The sea slug eats and steals chloroplasts from the alga Vaucheria litorea. The sea slugs then incorporate the chloroplasts into their own digestive cells, where the chloroplasts continue to photosynthesize for up to nine months – that’s even longer than they would perform in algae. The sea slugs stay nourished thanks to the sugars produced by photosynthesis.
[In this image] Elysia chlorotica, a sea slug steals photosynthetic chloroplasts from algae.
Photo source: Mary S. Tyler/PNAS
Key takeaways
- Autotrophs can produce their own nutrients from inorganic materials through either photosynthesis or chemosynthesis.
- Heterotrophs do not produce their own food. They live by eating other organims to obtain the energy source.
