In an ecosystem, which factor includes interactions among living organisms such as predation and competition?

• A. Biogeochemical Cycle
• B. Biological Factor
• C. Chlorophyll
• D. Denitrifying Bacteria

Answer: (B)

The key idea is that interactions among living organisms are biotic relationships. Predation, competition, and other interactions occur between living components of an ecosystem and help determine how populations rise or fall and how communities are structured. That’s why Biological Factor is the best choice here—it directly refers to the living parts of the ecosystem and their interactions.

Biogeochemical cycles describe the movement of elements through living and nonliving parts of the system (abiotic processes and their connection to life), chlorophyll is a pigment involved in photosynthesis, and denitrifying bacteria are organisms playing a role in a nutrient cycle but don’t denote the category of living interactions by themselves.