Concept:The biosphere is the global ecological system that includes all living organisms and their environments, making it the largest ecosystem on Earth.
Explanation:The biosphere covers all ecosystems such as forests, oceans, deserts, and grasslands.
It integrates the lithosphere (land), hydrosphere (water), and atmosphere (air).
Life exists from the deepest ocean trenches to the lower atmosphere.
The biosphere regulates climate, supports food chains, and maintains nutrient cycles like carbon and nitrogen cycles.
It contains all biological diversity, including plants, animals, and microorganisms.
Other options are smaller components: hydrosphere is only water bodies, lithosphere is only Earth's solid crust, and a biome is a large regional ecosystem.
Only the biosphere encompasses everything living and non-living that supports life on a global scale.
Answer:Option A (Biosphere)