In basic geography, what is the term for the part of the Earth where life exists and interacts with land, water and air?

Introduction / Context:
Geography often divides the Earth into different spheres to describe various physical components, such as air, water and rocks. This question focuses on a very standard definition that learners must remember for school level exams and competitive tests. It asks which sphere of the Earth includes all zones where living organisms are found and where they interact with the environment.

Given Data / Assumptions:
- The question is about the part of Earth where life exists.
- The options are biosphere, atmosphere, lithosphere and hydrosphere.
- We assume the student knows that life can exist on land, in water and even in the lower layers of the air, so the correct term must cover all these regions.

Concept / Approach:
The term biosphere is derived from two words: bio meaning life, and sphere meaning a round body like the Earth. The biosphere therefore includes all regions of the Earth where life is present. It cuts across other spheres such as the atmosphere, lithosphere and hydrosphere. For example, plants and animals live on the surface of the land, in the soil, in rivers and seas and in the lower atmosphere. All these life containing regions together form the biosphere.

Step-by-Step Solution:
Step 1: Identify what the question is really asking: the overall zone of life on Earth, not just one physical component like air or water. Step 2: Recall the meanings of the options: atmosphere is the envelope of gases, lithosphere is the solid outer part of Earth including rocks and soil, hydrosphere includes all water bodies and water in different forms, while biosphere refers specifically to the realm of living organisms. Step 3: Observe that life uses air, water and land together and is not limited to only one of these separate physical spheres. Step 4: Conclude that the only term that explicitly refers to the zone of life across all these environments is biosphere.

Verification / Alternative check:
Standard geography textbooks and diagrams show overlapping of spheres, where the biosphere is drawn as a thin but extensive layer that includes the lower atmosphere, surface waters and upper portions of the lithosphere. This confirms that biosphere is the correct technical term for the part of Earth where life exists and functions.

Why Other Options Are Wrong:
Atmosphere: This is the gaseous envelope around the Earth. While some organisms live in the air, the atmosphere itself is not restricted to zones of life and extends well beyond them.
Lithosphere: This is the outer solid crust and upper mantle. It includes both lifeless rocks deep below and life bearing soil near the surface. The term does not mean the life zone alone.
Hydrosphere: This includes all water on Earth in oceans, rivers, lakes, glaciers and underground. Many parts of the hydrosphere are not inhabited by organisms, so it is not equivalent to the biosphere.

Common Pitfalls:
Learners sometimes pick atmosphere or hydrosphere because they associate life with air or water. Another common error is thinking that biosphere refers only to plants and forests, when in fact it covers all living forms, including micro organisms and life in extreme environments. Remembering the root word bio as life helps avoid confusion.

Final Answer:
The part of the Earth where life exists is called the biosphere.