Energy Flow Through an Ecosystem

Sun is the principal source of all energies of the Earth. Biological activities require the utilization of energy that ultimately comes from THE SUN. The solar energy is captured by the green plants and transformed into chemical energy and bound in glucose as potential energy during the process of Photosynthesis. This potential energy is transformed into kinetic energy during respiration by the living world. In the biosphere the flowing of energy is unidirectional i.e. energy flows from the Sun to producers (mainly green plants) and then to all the members of the next trophic levels i.e. to the heterotrophic organisms (consumers, decomposers etc.) but never goes back to it's original sources.

The transformation of energy takes place in three successive steps, a) acquisition of energy, b) use of energy, and c) unidirectional flow of energy.

The microorganisms carry out their metabolic activities from decomposed plant and animal substances.

FLOW OF ENERGY

Energy after it is being accumulated by the primary producer is transferred through a food chain to different trophic levels. This phenomenon is called energy flow. According to Lindemann (1942), about 10% of total energy is transmitted, during flow of energy through several trophic levels. This is known as 10 % law.

A) Pathway of energy flow :

1) Through Grazing food chain : It is started from a green plant base, goes to grazing herbivores and onto carnivores like :

GRASS -------> HERBIVORES-----> CARNIVORES

2) Through detritus food chain : It starts from dead organic matter (DOM) to microorganisms and then to others like :

DOM ------->Bacteria and fungi --------> Insect larvae --------> Fishes.

B) Principles of energy flow :

Energy flow through food chain occurs as two laws of Thermodynamics, which are generally applied to closed systems. The first law of thermodynamics is the law of conservation of energy, which states that energy may be transformed from one form to another but, is neither created nor destroyed. If an increase or decrease occurs in the internal energy (E) of the system itself, Work (W) is done and Heat (Q) is either evolved or absorbed. Thus we can write that,

∆ E = W + Q

∆ refers to a change in quantity. In ecosystem energy inflows balance outflows as required by the first law of thermodynamics.

The second law of thermodynamics states that processes involving energy transformation will not occur spontaneously unless there is degradation of energy from a non-random to a random form. In an ecosystem each energy transfer is accompanied by dispersion of energy into unavailable heat (i.e. respiration) as required by the second law.

C) Process of energy flow :

Organic food (Glucose) is produced by the process of Photosynthesis. The total amount of solar energy converted into chemical energy by autotroph is called Gross Primary Production (GPP). A certain amount of GPP is lost by that particular autotroph through respiration and other physiological activities. The remainder is called Net Primary Production (NPP). Thus we can write :

NPP = GPP - autotrophic physiological functions.

This autotroph is consumed by primary consumers or herbivores, and then the energy input into the body of herbivores occurs. After transfer of energy from autotroph to primary consumer, energy loss occurs in primary consumers through respiration and other metabolic activities.

Finally least amount of energy is transferred from herbivore to carnivore by eating the former. In carnivore, energy is lost by respiration and other metabolic activities. Producers obtain their solar energy which is entrapped by the chlorophyll and cannot retrace its path, but released out to the environment.