Read the following passage carefully and answer the given questions.

Productivity in the Ecosystem

The flow of energy through a terrestrial ecosystem starts with the harnessing of sunlight by autotrophs. The radiant energy is converted by photosynthesis to organic compounds is known as productivity. The productivity is expressed in units of energy per unit of area per unit time. The amount of organic matter present at any given time is biomass. The productivity of any ecosystem is affected by many parameters like weather conditions, nutrient availability etc. The productivity of any ecosystem does vary seasonally and yearly.

The biomass available for consumption by herbivores and decomposers is known as-

Net Primary Productivity

The correct answer is Option (2) → Net Primary Productivity

Primary production refers to the amount of biomass or organic matter produced per unit area over a given time period by plants during photosynthesis. It is commonly measured in terms of weight (grams per square meter, g m^–2) or energy (kilocalories per square meter, kcal m^–2). Productivity, on the other hand, represents the rate of biomass production and is expressed as grams per square meter per year (g m^–2 yr^–1) or kilocalories per square meter per year (kcal m^–2 yr^–1) to facilitate comparison between different ecosystems.

Primary production can be further divided into two components: gross primary productivity (GPP) and net primary productivity (NPP). Gross primary productivity represents the total rate of organic matter production during photosynthesis in an ecosystem. However, a significant portion of this energy is utilized by plants for their own respiration needs.

Net primary productivity, on the other hand, is the amount of organic matter available for consumption by heterotrophs, such as herbivores and decomposers. It is calculated by subtracting the energy used by plants for respiration (R) from the gross primary productivity (GPP):

GPP - R = NPP.