Laws Governing Energy Transformations

The storage and expenditure of energy in an ecosystem is in accordance with the laws of thermodynamics (basic laws of thermodynamics).

The first law of thermodynamics is the law of conservation of energy, which says that 'energy can neither be created nor destroyed but can be transformed from one form into another'.

In biological system, solar energy is converted into chemical energy and is stored in food materials as internal energy. If an increase or decrease occurs in the internal energy of the system, then it only indicates some work (W) is done and heat (Q) is either evolved or absorbed. It can be represented as,

 

 

Hence energy is not created or destroyed in the system but is only transformed from one form into another.

Second law of thermodynamics states that processes of energy transformation will not occur spontaneously unless there is degradation of energy from a non - random to a random form.

Energy transformations, which occur within the ecosystem are considered in ecological energetics. The quantity of solar energy entering the earth's atmosphere is about 15.3 x 10⁸ cals/m²/year

(1 cal = 4.184 J).

But the average amount of solar energy (per unit area per unit time) actually available to autotrophs depends upon their geographical location.

Only the photosynthetically active radiation (PAR) is the energy available to autotrophs. A major portion (90 - 95%) of this energy is lost in the form of heat of evaporation and sensible heat.

Around 1 to 5% is used for photosynthesis (primary production). Thus, at each transfer, heat energy (random form) dissipates. Hence the energy transfer is not 100% efficient and there is degradation of energy from a non-random to a random form.

 

 

Energy conserving efficiency is 1.5% for grassland, 0.9% for savannah, 0.81% for mixed forest, 5% for modern crops and 10 - 12% for sugarcane field.

Thus in an ecosystem there is,

a) constant flow or transfer of energy from sunlight through plants (producers) to animals (consumers) in the form of food.

b) a decrease in useful energy during each transformation or transfer at each successive trophic level

c) return of entire solar energy trapped by green plants back to the environment as heat.