Which statement best describes symbiotic relationships?

• A. They are always non-living interactions
• B. They require two unrelated species
• C. They can be mutualistic, commensal, or parasitic
• D. They are not found in aquatic environments

Answer: (C)

Symbiotic relationships are close, long-term interactions between two different species that live in direct contact with each other. In these associations, at least one partner benefits, and the outcome for the other partner can vary: both can benefit (mutualistic), one can benefit while the other is unaffected (commensal), or one can benefit at the expense of the other (parasitic). Examples include bees and flowers (mutualistic), barnacles on a whale (commensal), and tapeworms in a host (parasitic). This kind of interaction can occur in many environments, including aquatic ones. So describing symbiosis as having these three possible relationships is the best way to capture what it is.