Symbiosis

Living things often live together.

This is called symbiosis. Some friends help each other. This is called mutualism.

A clownfish lives near a sea anemone. The anemone protects the fish. The fish helps the anemone too.

Sometimes, one friend is hurt. This is called parasitism. A tiny worm can live inside a host.

The worm gets food from the host.

Other times, one friend is not hurt. This is called commensalism. A fly might carry a small mite.

The mite gets a free ride.

Some living things must live together to stay alive. Others can live alone. Nature is full of these links.

Symbiosis is when two different living things live together.

This can be a long-term link. Some living things must live together to survive. We call this obligate. Others can live on their own. This is called facultative.

There are many ways this works. In mutualism, both partners help each other. A clownfish lives near a sea anemone. The anemone protects the fish with stinging cells. The fish helps the anemone too.

In commensalism, one partner benefits. The other is not really helped or hurt. A small mite might ride on a fly.

In parasitism, one partner benefits but the other is harmed. A tapeworm can live inside a host to get food.

Some live on the surface of another. This is ectosymbiosis. Others live inside the body of another. This is endosymbiosis. Bacteria can live in the roots of plants.

Symbiosis is a special way that different living things live together.

This relationship can last for a very long time. Some partners are obligate, which means they must live together to survive. For example, fungi and certain algae must stay together to form lichens. Other partners are facultative, meaning they can live on their own if they need to. Scientists study these connections to see how life works on Earth. These links help many species find new places to live.

There are many ways these partners interact with each other. In mutualism, both living things benefit from the relationship.

A clownfish gets protection from a sea anemone's stinging cells. In return, the fish helps the anemone by eating small creatures. Commensalism is different because only one partner gets help.

A small mite might ride on a fly for a free trip. Parasitism happens when one partner benefits but the other is harmed.

A tapeworm can live inside a host to take its food.

People have studied these living connections for a long time. In 1877, Albert Bernhard Frank used the word symbiosis for lichens. A few years later, a German scientist named Heinrich Anton de Bary gave a broader definition. In 1879, he said symbiosis is the living together of unlike organisms. Later, in 1949, Edward Haskell suggested a new way to group these interactions. These scientists helped us understand how different species act toward one another.

Living things can live on the surface of a partner or inside them. Ectosymbiosis is when a partner lives on the outside, like lice on humans.

Endosymbiosis is when one partner lives inside the tissues of another.

Bacteria live inside the root nodules of legume plants to help them. Some algae even live inside the cells of reef-building corals. These tiny bacteria can provide essential nutrients to about 10% to 15% of all insects.

You can see symbiosis in many places in nature. Ants live on acacia trees to protect them from harm. Insects help flowers grow by moving pollen from one to another.

Even hermit crabs use shells left behind by other animals for safety.

These connections show how everything in nature is linked together.

Symbiosis describes any close and long-term biological interaction between two organisms of different species.

The term comes from the Ancient Greek words for "living with" and "companionship." While some people use the word to mean only relationships where both sides benefit, scientists use it more broadly. It covers many different ways that life forms interact over time. These connections are vital because they can drive the evolution of entire species. For example, mutualism has helped species colonize brand new environments across the planet.

Scientists classify these interactions based on how they affect the fitness of the participants. Fitness refers to how well an organism can survive and reproduce. If an interaction reduces the fitness of both parties, it is called competition.

In competition, organisms often fight for a limited supply of resources like food, water, or territory. If only one party is harmed while the other remains unaffected, the relationship is called amensalism. This can happen through competition or antagonism. Antagonism occurs when one organism is killed or damaged by a chemical secretion. For instance, the black walnut tree secretes a substance called juglone to harm nearby plants.

Other relationships are defined by who gains an advantage. Commensalism occurs when one organism benefits but the other is not significantly helped or harmed.

This can involve using another organism for transportation, known as phoresy, or for housing, called inquilinism. In contrast, parasitism is a relationship where one organism benefits at the expense of the host.

Parasites can be endoparasites living inside a body or ectoparasites living on the surface. About 40% of all animal species are parasites. Finally, mutualism is a relationship where both parties benefit from the interaction.

This can be a highly specialized partnership that improves the competitive ability of both organisms.

Symbiotic relationships can also be categorized by where the organisms live in relation to one another. Ectosymbiosis occurs when a symbiont lives on the surface of a host. This includes things like lice on humans or barnacles on whales. Endosymbiosis is when one partner lives inside the tissues of another.

Endosymbionts can live between cells or even inside them. Some bacteria provide essential nutrients to about 10% to 15% of all insect species. These internal bacteria often have a much reduced genome because they adapt to the environment inside their hosts. They may even lose genes for metabolism or DNA repair over time.

These connections can also be defined by how much the partners rely on each other. An obligate relationship is one where one or both organisms depend on each other for survival. In lichens, the fungal partners cannot live on their own, making the relationship obligate for them. However, the algae in the lichen can often survive alone. This makes the algae's role facultative, or optional. A facultative symbiosis is one where the partners can still live independently.

An example is the relationship between certain hermit crabs and encrusting bryozoans.

The history of defining symbiosis has involved much debate among scientists. In 1877, Albert Bernhard Frank used the term to describe the mutualism found in lichens. In 1878, the German mycologist Heinrich Anton de Bary provided a broader definition. He described it as "the living together of unlike organisms." This definition was debated for 130 years as scientists argued over whether to include all long-term interactions or only mutualisms. In 1949, Edward Haskell proposed an integrative approach. He classified these biological connections as "co-actions," which biologists later adopted as "interactions."

Symbiosis is a fundamental part of how biological systems function. It is seen in the nitrogen fixation performed by bacteria in the root nodules of legumes.

It is also seen in the way insects pollinate flowers.

Even the very existence of complex life is linked to symbiosis. The process of symbiogenesis is thought to have helped create eukaryotes. This happened when bacteria were incorporated into cells to become mitochondria and chloroplasts. From tiny bacteria in insect guts to massive coral reefs, symbiosis connects the living world.