Autotrophs – Definition, Types, Examples, And Vs Heterotrophs

What exactly is autotrophy? How does it differ from heterotrophs? And why should you care?

Autotrophs - Definition, Types, Examples, And Vs Heterotrophs

If you are keen to learn more about Autotrophs in general or are just a fan of microbiology, then read on for all you need to know and learn.

What Are Autotrophs?

Autotrophic organisms (also known as autotrophs) are those that produce their own organic carbon compounds – that is, food – through using energy from light, as well as carbon dioxide, and water to undergo a process known as photosynthesis.

Some autotrophic organisms will also use chemical energy as an alternative to light energy, but the key thing to remember is that autotrophs use inorganic sources – also known as non living material – in order to make and produce food independently.

In contrast, heterotrophic organisms obtain energy and nutrients by consuming other living things or dead matter – they are not able to make or produce their own energy and food.

The ability of autotrophs to produce independent food means that they are often referred to as “primary producers’, and they hold a position at the very bottom of the overall food chain.

They can be found in a range of environments, including aquatic and marine environments, and on land, where they primarily reside in the soil.

Autotrophs are essential to life on Earth because they provide us with food and oxygen.

They also play a key role in maintaining our planet’s ecosystems. Heterotrophs, however, are responsible for the majority of human waste production.

What Are Some Common Types Of Autotrophs?

Algae: Algae are one of the oldest groups of autotrophs, and are single-celled organisms that reside in oceans and lakes.

Most algae are unicellular, but some species are multicellular. 

There are several different kinds of algae, including green algae, red algae, blue-green algae, and brown algae.

Bacteria: Bacteria are another group of autotrophs that are found everywhere on Earth. They are prokaryotic cells, meaning that they do not have a nucleus like eukaryotes do.

The majority of bacteria are aerobic, meaning that they require oxygen to grow.

Many bacteria can break down complex molecules into simpler ones, making them useful in industries such as biotechnology.

Plants: Plants are probably the best-known form of autotroph.

They are multicellular organisms that use photosynthesis to convert carbon dioxide and water into carbohydrates.

Plants are very important because they provide many essential nutrients to animals and to humans, and common examples include wheat, grasses, maize plants, and trees. 

How Can We Define An Autotrophic Organism?

An autotroph is any organism that uses sunlight to synthesize its own food. This includes algae, bacteria, fungi, mosses, trees, and more.

There are two main ways that autotrophs obtain their food:

  • Photosynthesis: Light-dependent reactions occur within the chloroplasts of green plants, cyanobacteria, and red algae.

During photosynthesis, carbon dioxide gas (CO2) combines with water molecules to form glucose.

Glucose is then converted into organic compounds like amino acids, fatty acids, nucleic acids, and vitamins.

  • Respiration: Respiration occurs in aerobic organisms, including animals, fungi, and bacteria.

During respiration, oxygen is released from cells through the activity of enzymes called cytochromes.

The oxygen is then used by other cells to make ATP, which provides the energy needed to carry out cellular functions.

Types Of Autotrophs

There are two main types of autotrophs: photoautotrophs and chemoautotrophs.

These are categorized according to the way in which their food is produced, and both types  thrive in a range of environments and surroundings.

They also use different materials and mechanisms in order to produce the energy that they need.


Photoautotrophs rely on energy derived from sunlight to perform photosynthesis, and this produces organic material – or food – using a combination of water and carbon dioxide.

The majority of organisms in this category contain chloroplast and a membrane-bound nucleus to carry out the required process. These are known as eukaryotic organisms.

Some prokaryotes, including several bacteria, are also able to undergo the process of photosynthesis to create energy.

Examples of photoautotrophs are:

  • Higher Plants such as trees, grass, and maize plants
  • Green algae
  • Bacteria
  • Euglena


Cyanobacteria are a specific type of organism, and these are the only bacteria that have the ability to generate oxygen during the photosynthesis process – this is something that no other bacteria has the ability to achieve.

This is because while cyanobacteria do not have chloroplasts included in their structure, they do contain chlorophyll, which helps them to capture energy from sunlight and use this to undergo the process of photosynthesis.

In more complex plants, such as trees or grasses, the process of photosynthesis occurs in a part of the leaf known as the mesophyll layer – this is home for the chloroplasts.

The carbon dioxide uses small openings known as stomata, located on the leaves, to get into this mesophyll layer and, in turn, the chloroplast.

The stomata are usually located on the underside of each leaf, and this helps to keep the water that is lost through transpiration to a minimum. 

The stomata take in carbon dioxide, and the root hairs of the plant then take in water from soil around them through osmosis.

This water then moves to the leaves and any other relevant areas of the plant via the vascular tissues known as the xylem.

Within this chloroplast is chlorophyll, and this is found in the thylakoid membrane – the outermost membrane of the cell.

The chlorophyll can absorb blue and red light wavelengths, and these, in turn, provide the energy that is needed for photosynthesis to occur.

What Is Photosynthesis?

Photosynthesis is the process by which green plants convert solar radiation into chemical energy.

It involves the absorption of light energy by pigments called chlorophylls, which are contained within the cells of the plant.

Chlorophyll absorbs light at certain wavelengths (the spectrum of visible light) and converts it into an electrochemical potential difference across the plasma membrane.

This potential difference is used to drive an electron transport chain in the chloroplast that results in ATP synthesis, essentially providing the energy to the organism.

The primary product of photosynthesis is glucose, which provides the raw materials for all living things – this will likely be a name that is familiar to athletes, thanks to the inclusion of glucose in a number of sports energy products.

Glucose is made up of six carbon atoms joined together with hydrogen bonds, and in order to make glucose, the plant must first break down the complex carbohydrates stored in its cells via the process of glycolysis.

Phases Of Photosynthesis

Phases Of Photosynthesis

There are two main stages to photosynthesis: the light-dependent phase and the light-independent reactions.

Light-Dependent Phase (Light Dependent Reactions)

The light-dependent phase of photosynthesis, which occurs in the thylakoid membrane, located in the chloroplast, is so named because it occurs in the presence of light energy, and the key function is to convert the light energy from the sun into chemical energy (NADPH and ATP). The chemical energy then allows plants to synthesize organic material for energy.

Essentially, this phrase has two photosystems – Photosystem I and Photosystem II.

Both of these include chlorophyll, and this absorbs the light to generate the energy needed to move electrons from the water molecules through the photosystems.

Light-Independent Phase (Light Independent Reactions)

During the light-independent phase of photosynthesis, there is no need for sunlight.

Instead, the sources of energy produced in the light-dependent phase (NADPH and ATP) produce the energy required to synthesize sugar.

The first stage of the light-independent phase is known as the Calvin cycle, and this combines ribulose 5, 5-bisphosphate, and carbon dioxide (RuBP) in the presence of the RuBP carboxylase/oxygenase (RuBisCo) enzyme.

This reaction creates two molecules of 3-phosphoglyceric acid (3PGA) – a fixed carbon compound in a process known as carbon fixation.

This is the first step in the light-dependent reaction stage.

The second stage, referred to as reduction, takes the NADPH and ATP produced in the light-dependent stage, and these sources are used to provide energy that converts the 3-phosphoglyceric acid into a three-carbon sugar – glyceraldehyde-3-phosphate (G3P).

In the third stage – regeneration – some of these glyceraldehyde-3-phosphate produce sugar molecules, or glucose, which provide energy.

Others are recycled and used to regenerate more RuBP to facilitate more reactions. ATP is used as the energy source for this stage.

What Is Chlorophyll?

Chlorophyll is a pigment found in most organisms; it helps them absorb light and use the energy they gain from it to create sugars.

There are two main types of chlorophyll: chlorophyll A, and chlorophyll B.

Chlorophyll A:

This type of chlorophyll is the most common type, and is located in most of the photoautotrophs – this includes algae, higher plants, and cyanobacteria.

Chlorophyll A captures both orange-red and blue-violet light, and reflects green light – it, therefore, appears green in color.

The energy that is captured from these wavelengths is used in the photosynthesis process.

Chlorophyll B:

Chlorophyll B is most commonly found in plants and algae.

This type of chlorophyll catches green light, and moves energy from light to the chlorophyll, alongside Chlorophyll A while absorbing a wider spectrum.

This type is most commonly produced where sun and light are more limited.

What Is Anoxygenic Photosynthesis?

As we have mentioned, photoautotrophs use water and carbon dioxide during the process of photosynthesis- this allows them to produce a combination of oxygen and sugar and is powered by sunlight which is then transformed into chemical energy.

Cyanobacteria are a unique form of bacteria, and are alone in their ability to generate sugar and oxygen as the end result of photosynthesis – there are no other bacteria which have the ability to produce oxygen.

These other bacteria – those that are unable produce oxygen through photosynthesis – are known as obligate anaerobes.

They produce energy via a process that is referred to as anoxygenic photosynthesis.

Examples of organisms that use this include:

  • Chloroflexi
  • Purple bacteria
  • Heliobacteria
  • Green sulfur bacteria

These organisms still use sunlight to form their energy – hence a form of photosynthesis – but they do not need water as a source of protons; instead, this comes from gasses such as hydrogen sulfide, which fuel the reduction process. 


As we have mentioned, photoautotrophs get energy via the sunlight.

Chemotrophs, on the other hand, are able to obtain energy without sunlight, and instead gain energy from molecules that are within their environment.

There are two main groups of chemotrophs: chemoorganotrophs make use of organic molecules as their main form of energy, while chemolithotrophs use inorganic materials as their energy source.

Chemotrophs – also known as lithotrophs – include a number of bacteria included in this category, such as the bacteria that can be located in worms, deep beneath the sea, as well as nitrifying bacteria.

Many of these organisms reside in locations with no sunlight, and so inorganic material cannot be used for the biosynthesis process.

What Is Biosynthesis?

Biosynthesis is the conversion of chemicals into another chemical compound.

Essentially, this is the production of a chemical compound by a living organism, and it occurs when an organism uses either sunlight or inorganic matter (such as carbon) to create sugars and other compounds – in the case of chemotrophs, this is inorganic matter.

The process of biosynthesis is different from photosynthesis because it does not involve the creation of new molecules.

Instead, it involves the transformation of existing molecules into more complex molecules.

Biosynthesis is usually divided into three stages:

1. Prebiotic synthesis

2. Prokaryotic synthesis

3. Eukaryotic synthesis

The first stage is the prebiotic synthesis, which refers to the formation of simple organic molecules prior to the emergence of life.

The second stage is prokaryotic synthesis, which describes the evolution of simple cells, including bacteria, archaea, and eukarya.

Finally, the third stage is eukaryotic synthesis, which deals with the evolution of larger and more complex cells, including plants, animals, and fungi.

Chemotrophs use biosynthesis to obtain their energy, in the same way, that phototroughs will use photosynthesis for the same purpose.

Why Are Autotrophs Important?

Why Are Autotrophs Important?

In order to understand why autotrophic microbes are important, it is necessary to know what they do.

As we have mentioned, an autotroph is a microbe that obtains its energy directly from sunlight, rather than using organic material. 

In fact, autotrophs are essential for our existence: without them, we would not be here. They provide us with oxygen, food, and even many of the minerals that make up our bodies.

It is estimated that autotrophs account for about half of Earth’s biomass, and their position at the bottom of the food chain makes them absolutely essential to all other forms of life that exist on the planet.

The position that autotrophs hold as primary producers cannot be overstated; it is no exaggeration to say that these organisms are at the core of our existence.

These organisms also help to supply us with the oxygen that we breathe, and we rely on them to provide us with the food that we eat.

For example, plants use photosynthesis to create sugars which they then convert into starches, proteins, and fats.

Animals take advantage of these carbohydrates to build muscle mass and store fat, while fungi and bacteria turn the starch into cellulose which is used to form cell walls.

What Are Heterotrophs?

Heterotrophs are those organisms that consume organic materials such as plant matter, animal tissue, and dead organisms in order to extract the energy that they need to survive.

These organisms are known as heterotrophs because they feed off of something else.

In contrast, autotrophs produce food through the use of light and the process of photosynthesis.

What Is Their Role In Our Environment?

As you may have guessed, heterotrophs play an incredibly important role in our environment. One of the most obvious examples of this is the decomposition of dead organisms.

When we die, our body breaks down, and some of the smaller pieces become part of the soil.

If there were no heterotrophs present, then these small parts would eventually return to the atmosphere, where they could cause serious problems for living things.

Another example of how heterotrophs affect our environment is when they eat waste products. Waste products contain toxins and chemicals that are harmful to the environment.

However, if heterotrophs did not exist, then these substances would remain in the air or water until they were broken down by other organisms.

Additionally, heterotrophs can also be used to clean up oil spills and remove contaminants from water.

The Importance Of Autotrophs And Heterotrophs To Humans

Both autotrophs and heterotrophs play a key role in their wider environments.

While autotrophs are responsible for providing us with oxygen and nutrients, heterotrophs help to break down dead organisms so that they can be recycled back into the ecosystem.

Both types of organisms are vital to the survival of humans, and both are equally important.

Final Thoughts

Autotrophs have a key role to play in our wider environment, and in the stabilization and creation of ecosystems; without them, life on Earth would no longer be able to exist, and the planet would appear as a very different place.

Jennifer Dawkins