Explanation:

- Atmosphere:

- The layer of gases surrounding the Earth.

- It protects life by absorbing ultraviolet solar radiation.

- Not associated with living organisms directly.

- Biosphere:

- ?? Correct Answer: Refers to all life on Earth and their interactions with the environment.

- Includes ecosystems, living beings, and their relationships.

- The realm of all biological activity.

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- Lithosphere:

- The outermost layer of Earth, consisting of the crust and upper mantle.

- It's solid and rocky, hosting various geological activities.

- Not primarily linked with living organisms.

- Hydrosphere:

- Encompasses all water bodies on Earth.

- Includes oceans, lakes, rivers, and underground water.

- Vital for life but does not exclusively indicate living organisms.

Therefore, your understanding that the biosphere is the realm of living organisms and their environment is spot on.