Read the paragraph carefully and answer the following questions :
A constant input of solar energy is the basic requirement for any ecosystem to function and sustain. Primary production is defined as the amount of biomass or organic matter produced per unit area over a time perio

Question

Read the paragraph carefully and answer the following questions :
A constant input of solar energy is the basic requirement for any ecosystem to function and sustain. Primary production is defined as the amount of biomass or organic matter produced per unit area over a time period by plants during photosynthesis. It is expressed in terms of weight (gm⁻²) or energy (kcal m⁻²). The rate of biomass production is called productivity. It is expressed in terms of gm⁻² yr⁻¹ or (kcal m⁻²) yr⁻¹ to compare the productivity of different ecosystems. It can be divided into gross primary productivity (GPP) and net primary productivity (NPP). Gross primary productivity of an ecosystem is the rate of production of organic matter during photosynthesis. A considerable amount of GPP is utilised by plants in respiration. Gross primary productivity minus respiration losses (R), is the net primary productivity (NPP). Net primary productivity is the available biomass for the consumption to heterotrophs (herbivores and decomposers). Secondary productivity is defined as the rate of formation of new organic matter by consumers. Primary productivity depends on the plant species inhabiting a particular area. It also depends on a variety of environmental factors, availability of nutrients and photosynthetic capacity of plants. Therefore, it varies in different types of ecosystems.
(a) Name the factors that influence the primary productivity of an ecosystem. [1]
(b) Suppose the GPP of a grassland ecosystem is 2000 kcal m⁻² yr⁻¹ and NPP is 1200 kcal m⁻² yr⁻¹. Calculate the respiratory loss (R). [1]
(c) Why is all the primary productivity not available to herbivores for consumption? [1]
(d) Differentiate between GPP and NPP. [2]

Accepted Answer

>

> [!TLDR]
> Primary productivity is set by plant type, environment, nutrients and photosynthetic capacity; here respiratory loss R = 2000 − 1200 = 800 kcal m⁻² yr⁻¹; herbivores get only NPP because plants use much GPP in respiration; GPP is total photosynthetic production while NPP is what remains after respiration.
>
> From the CBSE/NCERT *Ecosystem* chapter (primary production):
>
> **(a) Factors influencing primary productivity:** the **plant species** inhabiting the area; **environmental factors** such as light, temperature, water/precipitation; **availability of nutrients**; and the **photosynthetic capacity** of the plants.
>
> **(b) Respiratory loss (R):** NPP = GPP − R, so
> $$R = GPP - NPP = 2000 - 1200 = 800\ 	ext{kcal m}^{-2}	ext{ yr}^{-1}.$$
>
> **(c) Why not all primary productivity reaches herbivores:** a **considerable part of GPP is consumed by the plants themselves in respiration (R)**. Only what is left after respiration — the **NPP** — is stored as plant biomass and is available for consumption by heterotrophs (herbivores and decomposers). So the *entire* primary production can never be passed on.
>
> **(d) GPP vs NPP:**
>
> | Gross Primary Productivity (GPP) | Net Primary Productivity (NPP) |
> |---|---| …

Concept understanding — Primary Productivity Factors

What the NCERT textbook says

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