Question

The NPP in a plant is 100 KJ. What is the body mass of the secondary carnivore?
(a) 100 KJ
(b) 10 KJ
(c) 1 KJ
(d) 0.1 KJ

Answer 1

Hint: The Net Primary Productivity of the plant is the amount of energy due to the maintenance and metabolism after subtraction from the Gross Primary Productivity. This much energy is stored by plants and then transferred to the consumers.

Complete answer
Net primary productivity accounts for the amount of organic matter left for use by consumers. Respiratory activities of the plants consume some energy and thus the left energy is consumed by primary consumers. Whereas, secondary productivity is the amount of organic matter produced by consumers.
Plants are the main producers on Earth. The energy that plants trap to photosynthesize is the energy that sustains life on Earth. The energy trapped by plants is 2-$10\%$ of photosynthetically active radiation (PAR) given by the Sun. So, plants that are the primary producers produce organic matter out of which a part is consumed by primary consumers, and others are used up in the respiratory activities of the plants.

Additional information
- The ecosystem has four important functions- productivity, decomposition, energy flow, and nutrient cycling. Productivity is the rate at which organic matter is produced when plants capture sunlight and use it to make food. Decomposition is the physical and chemical breakdown of organic remains or detritus with the help of decomposers or detritivores.
- Half of the total incident radiation from the Sun is photosynthetically active radiation or PAR and only 2-$10\%$ of PAR is used by plants to photosynthesize. Nutrient cycling is the cycling of nutrients in an ecosystem that is used repeatedly by different components of the ecosystem.

So, the correct answer is ‘100 KJ’.

Note:
According to the law of $10\%$, the biomass will be decreasing as it goes from bottom to top in the pyramid. The organisms that are present at the lowest trophic level of the pyramid will produce more biomass that is approximately 1 tonne and then they are eaten by the organism of the second trophic level where the energy is passed but with a decrease in $10\%$ of the biomass.