ENVIRONMENTAL BIOLOGY (TKA3104) LECTURE NOTES -4 Energy Flow

8/9/2019 ENVIRONMENTAL BIOLOGY (TKA3104) LECTURE NOTES -4 Energy Flow

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TKA 3104ENVIRONMENTAL BIOLOGY

Energy Flow in Ecosystems



Ten Percent Law

• Lindemann (1942) put forth ten percent lawfor the transfer of energy from one trophiclevel to the next.

• According to the law, during the transfer of organic food from one trophic level to thenext, only about ten percent of the organicmatter is stored as flesh. The remaining is lost

during transfer or broken down in respiration.



• Plants utilize sun energy for primaryproduction and can store only 10% of theutilized energy as net production available forthe herbivores. When the plants are consumedby animal, about 10% of the energy in thefood is fixed into animal flesh which isavailable for next trophic level. When acarnivore consumes that animal, only about10% of energy is fixed in its flesh for the

higher level.• So at each transfer 80 - 90% of potential

energy is dissipated as heat where only 10 -20% of energy is available to the next trophiclevel.





Energy Flow

• Energy is the capacity to do work. Solarenergy is transformed into chemical energy bythe process of photosynthesis, and is stored in

plant tissue and then transformed intomechanical and heat forms during metabolicactivities.

• The energy, in the biological world, flows from

the sun to plants and then to all heterotrophicorganisms such as microorganisms, animals

and man.





• Energy flow is the key function in anecosystem and it is unidirectional.

• 'The study of energy transfer at differenttrophic level is known as 'Bioenergetics'.



Laws Governing Energy

Transformations• The storage and expenditure of energy in an

ecosystem is in accordance with the laws of thermodynamics.

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

another'.



• In biological system, solar energy is convertedinto chemical energy and is stored in foodmaterials as internal energy. If an increase or

decrease occurs in the internal energy of thesystem, then it only indicates some work (W)is done and heat (Q) is either evolved orabsorbed. It can be represented as,



• Hence energy is not created or destroyed inthe system but is only transformed from oneform into another.

• Second law of thermodynamics states thatprocesses of energy transformation will notoccur spontaneously unless there isdegradation of energy from a non - random to

a random form.



• Energy transformations, which occur withinthe ecosystem are considered in ecologicalenergetic. The quantity of solar energy

entering the earth's atmosphere is about 15.3x 108 cals/m2 /year.

• But the average amount of solar energyactually available to autotrophs depends upontheir geographical location.



• Only the photosynthetically active radiation(PAR) is the energy available to autotrophs. Amajor portion (90 - 95%) of this energy is lost

in the form of heat of evaporation and sensibleheat.

• Around 1 to 5% is used for photosynthesis.Thus, at each transfer, heat energy dissipates.Hence the energy transfer is not 100%

efficient and there is degradation of energyfrom a non-random to a random form.



• Energy conserving efficiency is 1.5% forgrassland, 0.9% for savannah, 0.81% formixed 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 eachtransformation or transfer at each successivetrophic level

c) return of entire solar energy trapped by

green plants back to the environment asheat.



Food Chain and Food Webs

"Food chain is a series of groups of organismscalled trophic levels, in which, there isrepeated eating and eaten by so as to transferfood energy".

Or"The series of populations or organisms of an

ecosystem through which food and energycontained in it passes with each memberbecoming the food of the later is called a foodchain".



For e.g.,

a) Food chain observed in a river:

b) Food chain observed in a pasture:



• The transfer of food energy from plant sourcesthrough a series of organisms forms a 'foodchain'.

• The base of the food chain is always formedby a plant (producer / autotroph), which isgrazed on by a herbivore, which is predatedover by a carnivore, which may be eaten by

another carnivore.



A food chain, can therefore, be represented as,

where each link represents a trophic level.

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ENVIRONMENTAL BIOLOGY (TKA3104) LECTURE NOTES -4 Energy Flow

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