Biosphere is best described as "all parts of the Earth where life exists."
The biosphere is the layer of the Earth where living organisms are found. This includes all the different ecosystems on the planet, such as forests, oceans, and deserts, as well as the living organisms that inhabit them. The biosphere extends from the deepest parts of the ocean to the highest mountains, and includes all the living things on Earth.
The biosphere is a complex system of interactions between living organisms and their environment. It is constantly changing and adapting to new conditions, and is made up of a diverse array of species that depend on each other for survival. Humans are a part of the biosphere, and we rely on it for our survival as well.
The other options given do not accurately describe the biosphere. The non-living parts of an ecosystem are known as the abiotic factors, while the living parts are known as the biotic factors. A component of an ecosystem can refer to any part of an ecosystem, such as a population, community, or habitat. All the members of a single species in a habitat are known as a population.
Therefore, the best description of the biosphere is "all parts of the Earth where life exists."