what do autotrophs do during photosynthesis

What do autotrophs do during photosynthesis? The process is quite fascinating and is something that plants and many other organisms use to produce energy.

Unlike humans, who can go grab something to eat from their pantries, plants need a different mechanism for energy production.

They use sunlight to initiate a chemical process that helps them produce their own food.

But what is the energy autotrophs use to make food in the first place?

The truth is that autotrophs use solar energy during photosynthesis to convert carbon dioxide and water into glucose, which they use as food.  

Getting Familiar with Autotrophs in the Real World

Before digging deeper into how autotrophs survive through photosynthesis, you need to be clear about exactly what falls into that category.

green plant hit by sunlight

Essentially, any organism capable of producing its own food is called an autotroph.

What do autotrophs produce during photosynthesis? It is glucose, which they use as their food to survive.

These autotrophs could be anywhere, but plants are the most common type of autotrophs, and they produce food using a process called photosynthesis.

Since they do not need to rely on other organisms for food, they are often called producers.

Fact: Glucose used during photosynthesis is also used as a building block to create cellulose and starch for extended energy storage. 

Different Types of Autotrophs Around you

As mentioned, plants are probably the most well-known type of autotrophs, but many other organisms also fall into this category.

algae in a body of water

For instance:

  • Algae live underwater and are considered autotrophic organisms.
  • Seaweed is a larger form of algae and falls into the same category.
  • Tiny organisms, like phytoplankton, in the ocean, are autotrophic organisms.
  • Various bacteria can produce their food and are a type of autotroph. 
Fact: To save energy throughout the colder months, plants produce less chlorophyll, which changes leaf color as chlorophyll synthesis declines. 

How Do Different Autotrophs Produce Food and Energy?

Different organisms fall into the category of “autotrophs” and they all produce energy in the same way, using photosynthesis. 

Giant Kelp

A kelp forest is a marine ecosystem where giant kelp thrives. It is a type of seaweed, which is the larger form of algae.

Algae are what you find at the ocean’s bottom and are considered autotrophs.

They generate energy through photosynthesis and are therefore at the top of the food chain. 

giant kelp underwater

New Plants

Plants are always a common example of autotrophs and they can synthesize their own food from inorganic sources like oxygen and solar energy.

Again, photosynthesis is the process through which plants produce glucose from CO2 and sunlight.

Fact: Cellular respiration works in reverse as compared to photosynthesis and uses sugar and oxygen to release carbon dioxide, energy, and water.  

What Do Autotrophs Do During Photosynthesis?

Green algae and plants use a process called photosynthesis to create their own food from the light they absorb. 

direct sunlight in plants

From microscopic mosses to massive fir trees, all are able to synthesize, or make, their own sustenance.

They harness solar energy for the process of photosynthesis, wherein they combine soil water and atmospheric carbon dioxide to produce glucose.

Glucose, a simple sugar, is used as a fuel source by plants. Cellulose, an essential component of plant growth and cell wall construction, is produced from glucose. 

Feeding the Plants

Putting a plant in soil, watering it, or exposing it to sunlight are all activities people perceive to be “feeding” the plant, but in reality, none of these things are actually food.

Instead, plants produce glucose, a kind of sugar they require to exist, from sunshine, water, and gases in the air.

All this happens through photosynthesis carried out by all algae, plants, and even certain bacteria.    

The Fascinating Process of Photosynthesis

Photosynthesis relies on plants taking in and using carbon dioxide. The microscopic pores in a plant’s leaves, stems, branches, and roots allow Co2 to enter the plant. 

up close photo of a leaf

The Role of Water

For plants to produce their own energy, water is essential. Water availability for a plant varies significantly from one setting to the next.

Interestingly, all photosynthetic organisms have some kind of adaption or particular structure that allows them to collect water.

Mostly, the roots of a plant are its primary water-absorbing organ. However, they all utilize different mechanisms to access water, and their needs are different too. 

For instance, a lilypad in a pond relies much more on the water than a cactus in a desert, but they both utilize some form of water to start photosynthesis. 

The Role of the Sun

During photosynthesis, autotrophs rely heavily on the sun.

leaves with red stem and sun

Without getting any energy from the sun, autotrophs simply cannot process water and CO2 to make glucose and release oxygen. The process actually works in different phases.

For instance:

  • The photosynthesis process creates sugar.
  • The mitochondria are responsible for converting the sugar into usable energy.
  • The cells utilize that energy for maintenance and development.
  • The process creates oxygen, which is expelled through the microscopic pores.

The released oxygen is not wasted, either, as animals and other species depend on oxygen to stay alive.

Fact: Other than plants, many other autotrophs use light for energy, including cyanobacteria, algae, and some protists. 

Autotrophs Using Photosynthesis Under Water

While it is quite evident how autotrophs above water produce food using photosynthesis, it can be confusing to know how it works underwater.

plants under water and sunlight

Interestingly, autotrophs under water also use photosynthesis to create energy and food.

The thing is that the sun’s energy can still travel through water and reach underwater organisms. And when photosynthesis happens, it leads to the release of oxygen.

Researchers have also found that these oxygen bubbles create a “ping” sound as they move up to the surface of the water. 

What do Aquatic and Land Plants Do During Photosynthesis?

The thing is that land and aquatic plants photosynthesize in the same way, at least chemically they work in the same fashion.

a variety of aquatic plants

If you really have to pinpoint a difference, it is likely to be how they access the “raw” material needed for photosynthesis. 

On the land, it works in a straightforward way:

  • Plants get water using their root system
  • They get CO2 from the air with the help of tiny holes in their leaves
  • They utilize solar energy to initiate the photosynthesis process.

Underwater, they get the three needed “ingredients” from their environment.

For instance:

  • They get CO2 and water from their aquatic environment.
  • They receive energy from the sun’s rays that travel through water

Do All Autotrophs Produce Food through Photosynthesis?

A large majority of autotrophs utilize photosynthesis to create their energy and food, but it is not true for every autotroph out there.

long under water plants

They are called autotrophs because they are self-sufficient when it comes to producing their own food.

However, they do not rely on photosynthesis but instead, use chemosynthesis.

What is special about chemosynthesis, you may ask? Well, plants using chemosynthesis:

  • Do not depend on the sun to get their energy.
  • Depend more on chemical reactions to produce food.

In other words, these autotrophs combine methane or hydrogen sulfide with oxygen to produce the food and energy required for their survival. 

Real-Life Examples of Autotrophs Not Using Photosynthesis

Interestingly, many organisms live in environments where they can find toxic chemicals and oxidize them to survive.

For instance, a good example is bacteria living in volcanoes where they can find enough sulfur to oxidize and turn into food.

Similarly, bacteria found in the deep ocean also utilize chemosynthesis to survive.

variety of plants

They are essential near hydrothermal vents, which are referred to as narrow cracks in the seafloor.

It is quite fascinating to see how this process works:

  • Seawater slowly enters the crack.
  • It seems down into the partly melted rock below.
  • The water becomes hot and circulates back up.
  • It recirculates into the ocean but contains minerals from the hot rock.
  • Bacteria use these minerals, including hydrogen sulfide to produce food. 


What do autotrophs do during photosynthesis? Autotrophs use the energy from the sun and utilize water and CO2 to produce glucose.

Each sugar molecule contains a fraction of the Sun’s energy that the plant can immediately put to use or reserve for later.

Interestingly, autotrophs utilize water even in environments where it is not readily available, like in desserts. And they also get CO2 and solar energy underwater, making photosynthesis work for them.