• Ecological Associations Between Organisms:
• Symbiosis (Obligate Symbiosis / Mutualism): An intimate, permanent, and obligatory physiological association between two different species where neither organism can survive independently under natural conditions (e.g., cellulolytic rumen protozoa/bacteria and ruminant hosts, or lichens).
• Commensalism: One organism benefits while the other is neither harmed nor helped; facultative and non-obligatory.
• Phoresis: Temporary transport association where a host mechanically carries another organism without physiological dependence.
• nalysis:
• (Symbiosis): Correct term for an obligatory and permanent interspecific partnership.

Correct option: (4) Symbiosis