Question

Read the following passage and answer the questions that follow:
"For any ecosystem, a constant input of energy is the basic requirement for its functioning and sustenance. The productivity of an ecosystem is calculated as the rate of biomass production expressed as gram/square meter/year ($\text{g}\cdot\text{m}^{-2}\cdot\text{yr}^{-1}$). The rate of production of organic matter during photosynthesis is called gross primary productivity (GPP). A considerable portion of GPP is consumed and utilized by plants during respiration. Therefore, the biomass available for heterotrophs is known as net primary productivity (NPP). The rate of formation of new organic matter by consumers is known as secondary productivity (SP).
Primary productivity depends on the plants species inhabiting a particular area, availability of nutrients, photosynthetic capacity of plants, and other environmental factors. The annual NPP of whole biosphere is approximately 170 billion tons, out of which, productivity of oceans is around 55 billions tons. In soil, the dead organic matter is converted to humans through humification. Humus undergoes slow degradation and is a reservoir of soil nutrients. Over a period of time, humus is further degraded by microbes and release nutrients by a process called mineralization."
41. Annual NPP of land area on the earth is ..............

• A. $< 55\text{ billion tons}$
• B. between 55 to 100 billion tons
• C. About 115 billion tons
• D. 225 billion tons

Hint:

Global Primary Productivity Distribution:
- Entire Biosphere = $170\text{ billion dry tons/year}$.
- Oceans ($71\%$ of surface) = $55\text{ billion tons/year}$ ($\sim 32\%$).
- Land ($29\%$ of surface) = $115\text{ billion tons/year}$ ($\sim 68\%$).
Terrestrial ecosystems produce roughly double the organic biomass of oceans.

Answer 1

The Correct Option is C

Concept:
The biosphere's Net Primary Productivity (NPP) is partitioned between terrestrial ecosystems (land) and aquatic ecosystems (oceans).
Terrestrial systems generate a disproportionately large share of global primary productivity relative to their surface area due to higher nutrient availability and direct access to sunlight.

Step 1: Extracting Quantitative Parameters from the Passage:
The passage provides the following values:
- Annual Net Primary Productivity ($\text{NPP}$) of the entire biosphere:
\[ \text{NPP}_{\text{total}} = 170\text{ billion tons (dry weight)} \] - Annual Net Primary Productivity ($\text{NPP}$) of oceanic ecosystems:
\[ \text{NPP}_{\text{oceans}} = 55\text{ billion tons} \]

Step 2: Calculating Terrestrial (Land) Productivity:
The biosphere consists of terrestrial and marine environments:
\[ \text{NPP}_{\text{total}} = \text{NPP}_{\text{land}} + \text{NPP}_{\text{oceans}} \] Rearranging to solve for the terrestrial component:
\[ \text{NPP}_{\text{land}} = \text{NPP}_{\text{total}} - \text{NPP}_{\text{oceans}} \] Substituting the given numbers:
\[ \text{NPP}_{\text{land}} = 170\text{ billion tons} - 55\text{ billion tons} = 115\text{ billion tons} \] Although oceans cover approximately $70.8\%$ of the Earth's surface, they contribute only about $55\text{ billion tons}$ due to light attenuation and nutrient limitation (such as nitrogen and iron).
Land ecosystems cover only $\sim 29.2\%$ of the surface but generate about $115\text{ billion tons}$ of biomass annually.
Final Answer:
The annual NPP of the land area on Earth is about 115 billion tons, corresponding to option (C).