Symbiosis is defined as which of the following?

• A. A close relationship between two or more different species
• B. Predation
• C. Competition for resources
• D. A long-term interaction that benefits both species

Answer: (A)

Symbiosis is a close relationship between two or more different species that live in direct contact with each other. This broad idea covers several types of interactions, including mutualism (both benefit), commensalism (one benefits, the other is unaffected), and parasitism (one benefits at the expense of the other). The reason this option fits best is that it focuses on the essential feature—the close, ongoing association between species—rather than the outcome for the species involved. The alternative describing a long-term interaction that benefits both points to mutualism, which is just one form of symbiosis, not the full concept. Predation and competition describe different ecological relationships: predation involves one organism consuming another, and competition involves species vying for the same resources without necessarily living in close, direct contact.