In environmental science, what is the term used for the global system formed by all the ecosystems of the earth taken together?

Introduction / Context:
Earth science distinguishes between many different spheres such as the atmosphere, hydrosphere, lithosphere, and biosphere. Each sphere describes a particular component of the earth system. Exams often ask candidates to differentiate between these terms. When we talk about all living organisms and their interactions with air, water, and land, we use the term biosphere, which effectively combines all individual ecosystems on the planet.

Given Data / Assumptions:
- The question asks which term refers to all the ecosystems of the earth taken together.- Options are biosphere, troposphere, stratosphere, and ionosphere.- We must choose the term that clearly relates to life and ecosystems.

Concept / Approach:
An ecosystem is a functional unit where living organisms interact with each other and their physical environment. When we consider all such ecosystems, from deep oceans to high mountains, we get a global ecological system. The correct word for this global ecological system is biosphere. In contrast, troposphere, stratosphere, and ionosphere are layers of the atmosphere named mainly by their physical and chemical characteristics, not by the presence of life.

Step-by-Step Solution:
Step 1: Recall the meaning of biosphere. It is the narrow zone of the earth where life exists and includes parts of land, water, and air where organisms are found.Step 2: Recognise that the phrase all ecosystems of the earth is basically another way of describing worldwide life and its habitats.Step 3: Check the other options. Troposphere is the lowest layer of the atmosphere where most weather phenomena occur, but it is not defined by ecosystems.Step 4: Stratosphere is the layer above the troposphere that contains the ozone layer, important for filtering ultraviolet radiation.Step 5: Ionosphere is a region of the upper atmosphere ionised by solar radiation, important for radio communication. None of these three terms refer to the totality of life and ecosystems.Step 6: Therefore, biosphere is the only option that correctly matches the description of all ecosystems of the world combined.

Verification / Alternative Check:
Standard textbooks in geography and biology define the biosphere as the global sum of all ecosystems. It is also referred to as the zone of life on earth. This textbook definition directly aligns with the wording of the question, confirming that biosphere is the correct answer.

Why Other Options Are Wrong:
Troposphere: Lowest layer of the atmosphere, important for weather but not used to denote all ecosystems.Stratosphere: Atmospheric layer containing the ozone layer, extending above the troposphere, again not an ecological term.Ionosphere: Upper atmospheric region significant for radio wave propagation, not for describing all living systems.

Common Pitfalls:
The main source of confusion is mixing terms with the suffix sphere and assuming they are similar. Some students may think of troposphere because most life and weather occur there, but the word troposphere does not include water and land ecosystems. To avoid mistakes, remember that bio relates to life, so biosphere naturally means the sphere of life, which neatly covers all ecosystems.

Final Answer:
Biosphere is the term used for the global system formed by all the ecosystems of the earth.