Download Symbiosis is a relationship between two organisms: it

Symbiosis is a relationship between two organisms: it can be
mutualistic (both benefit), commensal (one benefits), or parasitic.
LEARNING OBJECTIVE [ edit ]
Compare Mutualism and Symbiosis
KEY POINTS [ edit ]
Mutualism, a relationship in which both species benefit, is common in nature. In microbiology,
there are many examples ofmutualistic bacteria in the gut that aid digestion in both humans and
animals.
Commensalism is a relationship between species in which one benefits and the other is
unaffected. Humans are host to a variety of commensal bacteria in their bodies that do not harm
them but rely on them for survival (e.g. bacteria that consume dead skin).
Parasitic relationships, in which one species benefits and the other suffers, are very common in
nature. Most of themicroorganisms studied in medical microbiology are parasitic and feed on
human tissue. For example, cholera, leshmaniasis, and Giardia are all parasitic microbes.
Symbiotic relationships can also be classified by the physical relationship between the two
species. Endosymbionts live inside the tissues of the host, while ectosymbionts live outside of
their partner species.
TERMS [ edit ]
symbiosis
A close and often long-term interaction between two or more different biological species
mutualism
A relationship between individuals of different species in which both individuals benefit
commensalism
A class of relationship between two organisms in which one organism benefits without affecting
the other
Give us feedback on this content: FULL TEXT [edit ]
Symbiosis is any relationship between two
or more biological species. Such
relationships are usually long term and
have a strong impact on the fitness of one
or bothorganisms. Symbiotic relationships
are categorized by the benefits and
physical relationships experienced by each
species.
Common types of symbiosis are
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categorized by the degree to which each
species benefits from the interaction:
Mutualism: In mutualistic interactions, both species benefit from the interaction. A
classic example of mutualism is the relationship between insects that pollinate plants and
the plants that provide those insects with nectar or pollen. Another classic example is the
behavior of mutualistic bacteria in ecology and human health. Gut bacteria in particular
are very important for digestion in humans and other species. In humans, gut bacteria
assist in breaking down additional carbohydrates, out-competing harmful bacteria, and
producing hormones to direct fat storage. Humans lacking healthy mutualistic
gut flora can suffer a variety of diseases, such as irritable bowel syndrome . Some
ruminant animals, like cows or deer, rely on special mutualistic bacteria to help them
break down the toughcellulose in the plants they eat. In return, the bacteria get a steady
supply of food .
Commensalism: In commensalism, one organism benefits while the other organism
neither benefits nor suffers from the interaction. For example, a spider may build a web
on a plant and benefit substantially, while the plant remains unaffected. Similarly, a
clown fish might live inside a sea anemone and receive protection from predators, while
the anemone neither benefits nor suffers.
Parasitism: Parasites are organisms that harm their symbiotic partners. Parasitism is
incredibly common in nature: depending on the definition, more than half of all species
may go through at least one parasitic stage in their life cycle. There are many welldocumented examples of parasitic bacteria and microorganisms throughout this text.
Symbiosis can also be characterized by an organism's physical relationship with its partner.
Endosymbiosis: a relationship in which one of the symbiotic species lives inside the tissue
the other. For example, Coral polyps have special algae called zooxanthelle that live inside
their cells. Zooxanthelle provide sugars to the coral throughphotosynthesis. Similarly,
nitrogen-fixing fungi often live inside the cells of plants, providing nitrogen in exchange
for the sugars of photosynthesis.
Ectosymbiosis: a relationship in which one species lives on the outside surface of the
other. Barnacles that live on whales and bromeliads that live on tropical trees are
examples of endosymbionts.
These categories can be paired with the above terms to better describe the species'
interactions. For example, you might say that a gut bacteria is an "endosymbiotic mutualist,"
or that a flea is an "ectosymbiotic parasite. "