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2.  In biology, symbiotic refers to any
diverse organisms that live together,
but in this case, the relationship is
not necessarily beneficial to both.
Parasites, for example, have a
symbiotic relationship with their
hosts, but only the parasite benefits.

3.  Search Results
 Some symbiotic relationships are obligate,
meaning that both symbionts entirely depend
on each other for survival. For example, many
lichens consist of fungal and photosynthetic
symbionts that cannot live on their own.