Here's why:

* Ecosystem: An ecosystem is a community of living organisms (plants, animals, fungi, bacteria) in conjunction with the non-living components of their environment (like soil, water, air, sunlight). A tropical rainforest, with its diverse species interacting with each other and their environment, clearly fits this definition.

* Biome: A biome is a large-scale community of plants and animals characterized by its climate and vegetation. Tropical rainforests are defined by their high temperatures, heavy rainfall, and specific types of plants like broadleaf evergreen trees. This makes it a distinct biome.

So, a tropical rainforest is both a specific ecosystem with unique interactions within it and a larger biome with a distinct climate and vegetation.