Question

What is PAR in energy flow model

Answer 1

The energy flow in the ecosystem is one of the major factors that support the survival of such a great number of organisms. For almost all organisms on earth, the primary source of energy is the solar energy. It is amusing to find that we receive less than 50 percent of the sun’s effective radiation on earth. When we say effective radiation, we mean the radiation which can be used by plants to carry out photosynthesis.

Most of the sun’s radiation that falls on the earth is usually reflected back into space by the earth’s atmosphere. This effective radiation is termed as the Photosynthetically Active Radiation (PAR).

Overall we receive about 40 to 50 percent of the energy having Photosynthetically Active Radiation and only around 2-10 percent of it is used by plants for the process of photosynthesis. Thus, this percent of PAR supports the entire world as plants are the producers in the ecosystem and all the other organisms are either directly or indirectly dependent on them for their survival.

The energy flow takes place via food chain and food web. During the process of energy flow in the ecosystem, plants being the producers absorb sunlight with the help of the chloroplasts and a part of it is transformed into chemical energy n in the process of photosynthesis.

This energy is stored in various organic products in the plants and passed on to the primary consumers in the food chain when the herbivores consume (primary consumers) the plants as food and convert chemical energy accumulated in plant products into kinetic energy, degradation of energy will occur through its conversion into heat.

Then followed by the secondary consumers. When these herbivores are consumed by carnivores of the first order (secondary consumers) further degradation will occur. Finally, when tertiary consumers consume the carnivores, again energy will be degraded. Thus, the energy flow is unidirectional in nature.

Moreover, in a food chain, the energy flow follows the 10 percent law. According to this law, only 10 percent of energy is transferred from one trophic level to the other; rest is lost into the atmosphere. This is clearly explained in the following figure and is represented as an energy pyramid.

Answer 2

PAR means photosynthetically active radiation.
it means the part of total solar radiation which can be used for photosynthesis. less than 50% of the incident solar radiation is PAR. Plants capture 2–10 % of the PAR for photosynthesis.
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