Define biosphere.

Explanation

### Step-by-Step Solution:

1. **Definition of Biosphere**: The biosphere can be defined as the global sum of all ecosystems. It is the zone of life on Earth, where living organisms exist.

2. **Components of the Biosphere**: The biosphere consists of three main components:
- **Lithosphere**: This is the Earth's crust and upper mantle, which includes soil and rocks. It provides the necessary nutrients and minerals for life.
- **Atmosphere**: This is the layer of gases surrounding the Earth. It provides oxygen for respiration and carbon dioxide for photosynthesis, essential for life.
- **Hydrosphere**: This includes all the water bodies on Earth, such as oceans, rivers, and lakes. Water is vital for all living organisms.
...