The document discusses energy flow through ecosystems. It begins by explaining the two laws of thermodynamics - that energy cannot be created or destroyed, only transformed, and that entropy increases with each transformation. It then describes how solar energy is captured by producers via photosynthesis and passed through trophic levels, becoming less at each level due to energy lost as heat. Finally, it discusses ecological efficiencies like trophic transfer efficiency, where typically only about 10% of energy is transferred between trophic levels.

1. Energy Flow
The Earth is an open system of energy. It is the key function in the ecosystem.
The operation of an ecosystem is regular with the law laws of thermodynamics that deals
with the relationship between energy and matter in a system.
The behaviour of the energy in the ecosystem is based on two basic laws of
thermodynamics.
The first law of thermodynamics, which states that energy cannot be created nor
destroyed but only transformed. The first law of thermodynamics is also called as law of
conservation of energy.
The sun is the ultimate source of energy for almost all ecosystems present on the earth.
Photosynthetic organisms convert solar energy to chemical energy, but the total amount
of energy does not change.
The total amount of energy stored in organic molecule synthesized by the process of
photosynthesis plus the amounts dissipated as heat must equal the total solar energy
intercepted by the photosynthetic organisms.
In other words, energy may change form (from radiant to chemical) but not amount.
During energy transformation, some amount of energy is converted to form that’s usable.
In most cases, this unusable energy takes the form of heat.
Energy in the form of heat does not do work it goes to increase the randomness of the
universe. The degree of randomness or disorder in the system is known as entropy.
The second law of thermodynamics, states that every energy transformation that takes
place will increase the entropy of the universe in other words, every transformation
cannot be hundred percent efficient some energy is always lost as heat.
In ecosystems, energy flows unidirectionally. The fraction of incoming solar radiant
energy that the producers capture is small. Only about 1- 5% energy is incident solar

2. radiation 2-10% of PAR (Photosynthetically Active Radiant) is actually captured by the
photosynthetic processes. The solar energy not used for photosynthesis is immediately
converted to heat.
The flow of energy through an ecosystem
The energy that enters the ecosystem as solar energy (radiant energy) and is then passed a long as chemical energy to successive
trophic level. At its step energy is diverted meaning that the chemical energy available to each trophic level is less than that
available to the preceding trophic level. Death at each level transfers energy to decomposers. Energy lost as heat at each trophic
level is return to the external environment.
Energy flow model
A simplified representation of energy flow through ecosystem has been made in figure.
The model attempts to recognize the various inputs and weights of energy.
Two aspects with respect to energy flow in the ecosystem need careful consideration.
• First, the energy flows unidirectionally, it cannot be transferred in the
reverse direction.
• Second, the amount of energy flow decreases with successive trophic
levels.

3. Ecological efficiencies
In ecosystems, living organisms are linked together by feeding relationship.
Producers have the ability to fix carbon through photosynthesis via chlorophyll in their
leaves.
Herbivores are the primary consumers of organic molecule fixed by the producers.
Secondary consumers live on the organic molecule of the herbivorous.
There may be several levels of carnivorous in any one ecosystem search in such cases the
ultimate level will be occupied by the top carnivorous.
The final groups of organism in an ecosystem are decomposers, bacteria and fungi which
can break down the complex organic chemicals of death dead organism or dead material
and waste products.

4. Percentage of energy in the biomass produced by one trophic level that is incorporated
into the biomass produced by the next higher trophic level is called ecological efficiency.
It is also known as transfer efficiency or Lindeman’s efficiency.
The proportions of net primary producer production that flow along the possible energy
pathways depend on transfer efficiencies in the way energy is used and passed from one
step to the next.
Knowledge of three categories of transfer efficiency is required to predict the pattern of
energy flow. These are consumption efficiency (CE), assimilation efficiency (AE) and
production efficiency (PE).
Consumption efficiency or exploitation efficiency is the percentage of total productivity
available at one trophic level (Pn-1) that is actually consumed by a trophic compartment
one level up (In).
In the case of secondary consumer, it is the percentage of herbivores productivity eaten
by carnivores. Consumption efficiencies of herbivores are very low, reflecting either the
difficulty of utilizing plant material or the low herbivores densities.
Assimilation efficiency is the percentage of food energy taken into the guts of consumers
in a trophic compartment (In) that assimilated across the gut wall (An) and becomes
available for incorporation into growth or used to do work. The reminder is lost as feces
and enters the base of decomposer system.
Carnivorous have higher assimilation efficiency approx. 80% than herbivores that is
about 20-50% because animal food is more easily digested than plant food. In aquatic
ecosystem, autotrophs are mostly of small biomass but very low indigestible matters as

5. compared to their counter parts in the terrestrial ecosystem. Hence, herbivores
assimilation efficiency is higher in aquatic ecosystem than in terrestrial ecosystem.
Production efficiency is the percentage of assimilated energy (An) that is incorporated
into new biomass (Pn). The remainder is entirely lost to the community as respiratory heat.
Production efficiency is also known as net productivity efficiency or tissue growth
efficiency varies mainly according to taxonomic class of the organism concerned. In
vertebrates in general, have high efficiency (30- 40%) and among the vertebrates cold
blooded animals have intermediate values of PE around 10%. In warm-blooded animals
come with high energy expenditure associated with maintenance maintaining a constant
temperature, convert only one to 2% of assimilated energy into production. Similarly,
herbivorous tend to have higher production efficiency but lower assimilation efficiency
than carnivores.
Trophic transfer efficiency
Lindeman's law of tropic transfer efficiency or simply tropic efficiency states that the
efficiency of energy transfer from one trophic level to the next is about 10% i.e. about 10% off
the net primary productivity of producer ends up as herbivores, about 10% of the net productivity
of herbivores end up as primary carnivorous and so on.
In other words about 90% of energy available at one trophic level typically is not
transferred to the next. This loss is multiplied over the length of a food chain. For example, if
10% of available energy is transferred from primary producers to primary consumers and 10% of
that energy is transferred to secondary consumers then only 1% of net primary production is
available for next consumer i.e. 10% of 10%.