Final answer:
The biosphere is the part of Earth that supports life, encompassing land, water, and atmospheric regions where organisms can exist. Unlike an ecosystem or habitat, the biosphere refers to the global sum of all ecosystems.
Step-by-step explanation:
The portion of Earth that supports the existence of living things is the biosphere. The biosphere includes all parts of Earth where life exists, embracing many of the planet's environments, such as portions of land, bodies of water, and layers of the atmosphere. In contrast, an ecosystem refers to all the biotic and abiotic factors in a specific area and the interactions among them, while a habitat is the particular environment or place where a species or a community of species lives. Moreover, a niche defines the role of a species within its ecosystem, including its interactions with other organisms and its environment.