As such, sun is the ultimate source of all our energy, which caters to the need of our ecosystem. In the interior of the sun, a thermonuclear reaction is continuously going on at a temperature of about 108  K where in hydrogen is converted into helium. This is accompanied by a release of huge amount of energy, which manifests itself as heat and light. 

Observations made from artificial satellites indicate that nearly 30% of the total solar radiation entering our atmosphere is reflected by the earth-atmosphere system. The remaining 70% of the radiation is absorbed by the earth’s atmosphere. Of this 19% is absorbed directly by the atmosphere and the rest by the earth’s surface. The blue and red component (400-500 nm and 600-700 nm band respectively) of solar radiation are strongly absorbed by chlorophyll, the green pigment, present in vegetation and are converted into chemical energy. That is how energy for the ecosystem is trapped.

The energy captured by the autotrophs will never revert back to the sun. Similarly, the energy, which passes to the herbivore, does not revert back to autotrophs and so on. Thus, the flow of solar energy is unidirectional. In an ecosystem, energy is transferred in an orderly sequence.Its immediate implication is that an ecosystem would collapse if the sun stops giving out energy. The second important fact is that at each tropic level energy content decreases progressively. This factor is easily explained by noting that the trapped solar energy is used up in metabolic activity and measured as respiration.

The first laws of thermodynamics deals with the conservation of matter and energy and states that energy cannot be created or destroyed but can only change from one form to another. For example, the energy of visible light is absorbed by green plants through photosynthesis; it is changed into chemical energy stored in the glucose molecules. Almost all living organisms including plants consume glucose in respiration and use the stored chemical energy for their metabolic activity. Some of the energy is dissipated as heat, another form of energy.

The second law of thermodynamics states that some useful energy is converted into unusable waste heat during every energy transformation. This heat energy escapes into the surrounding environment.

The function of ecosystem describes the flow of energy and the cycling of nutrients. This includes the several aspects of an ecosystem,

(i) Energy flow

(ii) Food chain

(iii) Diversity pattern in time and spax

(iv) Nutrient cycles

(v) Development and evolution

(vi) Control

The solar energy is converted into chemical energy through photosynthesis by plants. These green plants are grazed by heterotrophy. This shows not only the chemical energy in the form of carbohydrates, fats and proteins but a host of other nutrients are transferred into herbivores. Such a process continues up to the decomposer level through the carnivores.

The two ecological processes of energy flow and mineral cycling involving interaction between the physico-chemical environment and the biotic communities may be considered the heart of the ecosystem dynamics. In an ecosystem, energy flows in non-cyclic manner (unidirectional) from sun to the decomposers via producers and macro-consumers (herbivores and carnivores) whereas minerals keep on moving in a cyclic manner.

Solar Energy –> Producer (autotrophs) –> Consumer (herbivores) –> Consumer (carnivores) –> Consumer (higher levels of carnivores)