Option 1: This option is partially correct. An ecosystem does consist of producers, consumers, and decomposers, but it also includes other living organisms and their interactions.

Option 2: This option is not entirely accurate. While plants and animals are indeed part of an ecosystem, an ecosystem consists of more than just plants and animals. It also includes non-living components such as air, water, soil, and climate, along with various interactions and relationships between organisms.

Option 3: This is the correct answer. An ecosystem consists of both the living community (which includes plants, animals, and microorganisms) and its environment (which includes non-living components and physical factors such as temperature, sunlight, and nutrients).

Option 4: This option is incorrect. An ecosystem is not limited to carnivores and herbivores. It includes a wide range of organisms, including decomposers, omnivores, and primary producers.