Which of the following is a biotic factor in an ecosystem?

In an ecosystem, biotic factors refer to the living components that interact with each other and their environment. Plants are considered a biotic factor because they are living organisms that play a critical role in the ecosystem. They produce oxygen through photosynthesis, serve as a primary food source for herbivores, and provide habitat and shelter for various organisms. Their presence and interactions with other biotic factors, such as animals, fungi, and bacteria, significantly influence the dynamics of the ecosystem.

In contrast, the other options represent abiotic factors. Water and sunlight are essential non-living components that affect the survival of biotic factors, but they themselves do not possess life. Soil, while it can support biotic interactions, is primarily a non-living component that provides nutrients and a medium for plant growth. Thus, plants are uniquely identified as a biotic factor among the choices provided.