Photosynthetic Microorganisms: The Reason Why We Are Alive

Updated: Jul 14, 2021

Although they may seem unimportant, photosynthetic microorganisms are the reason why we are alive right now. 50% to 80% of the world’s oxygen production comes from the ocean because the oxygen comes from microscopic organisms such as algae, phytoplankton, and cyanobacteria. These organisms perform photosynthesis, and that is what produces the oxygen. They also make the element carbon accessible to other marine organisms in a process called carbon fixation.


Out of all the photosynthetic microorganisms in the ocean, prochlorococcus is the team carrier. Prochlorococcus is the smallest photosynthetic organism on Earth, yet it is able to produce 20% of the oxygen in our biosphere, more than all the tropical rainforests combined, and it is responsible for 5% of global photosynthesis. This is because it is extremely abundant: there are about 3 billion billion billion prochlorococcus in the ocean, enough to make the mass of 220 million cars.

Prochlorococcus are a type of cyanobacteria. There are many variations, or ecotypes of it, depending on where it lives. They live anywhere in between 40 degrees South and 40 degrees North, a large amount of the ocean, so being genetically diverse would be extremely helpful for adapting in different climates. Each cell has about 2,000 genes, but the entire species has 80,000 genes.

Above: abundance of photosynthetic microorganisms. You can see prochlorococcus dominates the ocean.

Prochlorococcus may also be the reason why the Earth is full of life. Scientists think that prochlorococcus helped start life in the ocean and also helped fill up the Earth’s atmosphere with oxygen, making it a habitable place.

Carbon fixation

Besides producing oxygen so that humans like us are able to breathe, photosynthetic microorganisms also fixate carbon from carbon dioxide. This is important because many other organisms in the ocean need carbon but cannot use it directly from carbon dioxide.

Carbon fixation is a part of the light-independent cycle of photosynthesis and is also known as the calvin cycle. In carbon fixation, carbon atoms from carbon dioxide are continually fixated into a glucose molecule, until 6 carbon atoms are present to make an entire glucose molecule, C6H12O6.