The largest ecosystem of Earth is the Biosphere.

The Biosphere refers to the zone of life on Earth, where living organisms interact with each other and with their environment. It encompasses all parts of the planet that can support life, including the air, land, and water. The Biosphere is the largest and most complex ecosystem on Earth, as it includes all other ecosystems within it.

Explanation:

Biosphere:
The Biosphere is the sum of all ecosystems on Earth. It includes all living organisms, their interactions with each other, and their interactions with the physical environment. The Biosphere extends from the deepest parts of the ocean to the highest mountains, and from the polar regions to the equator. It includes various habitats such as forests, grasslands, deserts, wetlands, and marine ecosystems.

Hydrosphere and Lithosphere:
The Hydrosphere refers to all the water on Earth, including oceans, seas, lakes, rivers, groundwater, and atmospheric water vapor. It is an important part of the Biosphere, as it supports a wide range of aquatic ecosystems. However, the Hydrosphere alone cannot be considered the largest ecosystem, as it does not include terrestrial ecosystems.

The Lithosphere, on the other hand, refers to the solid outer layer of Earth, which includes the Earth's crust and the uppermost part of the mantle. It is the physical foundation of the Biosphere and provides the habitat for various terrestrial ecosystems. However, the Lithosphere alone cannot be considered the largest ecosystem, as it does not include the vast expanses of the oceans and other aquatic ecosystems.

Biome:
A biome is a large geographical region characterized by distinct climate, flora, and fauna. Examples of biomes include tropical rainforests, deserts, tundra, and grasslands. While biomes are important components of the Biosphere, they are not the largest ecosystem themselves. They are rather subdivisions within the Biosphere, each with its own unique characteristics.

Conclusion:
In conclusion, the largest ecosystem of Earth is the Biosphere. It encompasses all ecosystems on Earth, including terrestrial and aquatic habitats. The Biosphere is a complex web of interactions between living organisms and their environment, and it plays a crucial role in supporting life on our planet.