The set of all living organisms of different species in a lake constitutes which concept?

• A. Ecosystem
• B. Population
• C. Species
• D. Community

Answer: (D)

The concept being tested is the level of ecological organization that includes all living organisms of different species in a defined area. In a lake, this means every kind of plant, animal, and microorganism present, together forming a community, with their interactions like predation, competition, and symbiosis.

An ecosystem would also include the nonliving, environmental factors (water chemistry, temperature, nutrients) that affect those organisms, not just the organisms themselves. A population refers to all individuals of a single species in the area, and a species is a single biological group. So the set of all living organisms of different species in a lake best fits the idea of a community.