Solar energy enters ecosystems through photosynthesis by plants. Approximately 1% of solar energy is converted to chemical energy by plants through photosynthesis. Herbivores then consume plants to obtain this chemical energy, but approximately 90% is lost as heat or other forms of energy at each trophic level. There are several models that describe energy flow, including single channel models where energy moves in one direction from producers to consumers, and Y-shaped models where energy moves through both grazing food chains and detritus food chains.

1. ENERGY FLOW
THROUGH
ECOLOGICAL SYSTEMS

2. ENERGY FLOW IN THE ECOSYSTEMS
• Energy is the most essential requirement for all living organism.
• Solar energy is the only source to our planet earth. Solar
• energy is transformed to chemical energy in photosynthesis by the
plants (called as primary producers).
• Though a lot of sunlight falls on the green plants, only 1% of it is
utilized for photosynthesis. This is the most essential step to provide
energy for all other living organisms in the ecosystem.
• Some amount of chemical energy is used by the plants for their
growth and the remaining is transferred to consumers by the
process of eating.
• Thus the energy enters the ecosystems through photosynthesis
and passes through the different tropic levels feeding levels.

3. Energy flow andThermodynamics
The flow of energy through an ecosystem follows the two laws of thermodynamics.
1. I law of thermodynamics
It states chat “energy can be created nor destroyed, but it can be considered from one from to
another”.
Illustration
Energy for an ecosystems comes from the sum. It is absorbed by plants, herein it is converted
into stored chemical energy i.e., solar energy in converted into chemical energy.
2.II law of thermodynamics
Statement
It states that, “Whenever energy is transformed, there is a loss of energy through the
release of heat”.
Illustration
This occurs when energy is transferred between tropic levels. There will be a loss of
energy (about 80-90%) in the form of heat as it moves from one tropic level to another tropic
level. The loss of energy takes place through respiration, running, hunting etc.,

4. Photosynthesis
• A process in which light energy is transformed into chemical energy
generating food in form of sugar molecules.
• this occur in mesophyll (layer of cells at interior sections) of leaves
(inside the chloroplast) and stoma (gaseous exchange).
Two stages :
I) light dependent reactions (Chloroplast)
Solar energy + chlorophyll----------chemical energy (ATP, NADPH)
II) Light independent reactions: Calvin Cycle-
Energized electrons+ CO2 molecules -------------------Formation of products
the equation for photosynthesis is:
6 CO2 + 6H2O + light energy C6H12O6 + 6 O2

6. Facts : photosynthesis
• It is estimated that 99% of the energy used by living cells comes from
the sun
• Incorporation of sunlight into chemical bonds occurs through the
process of photosynthesis.
• Photosynthesis begins the carbon cycle by fixing CO2 (carbon dioxide
in the atmosphere).
• Oxygen is a waste product of photosynthesis. All oxygen in
atmosphere is believed to originate from photosynthesis.
• The oxygen released as a by-product has a major impact on the
biosphere. Today's atmosphere would not have 21% oxygen if not for
photosynthesis.

8. Relationship between structure and function (flow model)
The biotic components and abiotic components are linked
together through energy flow and nutrient cycling as
shown in the following figure.

9. Lindeman’s 10% law of energy flow
• Lindemann (1942) put forth ten percent law for the transfer of
energy from one trophic level to the next.
• According to the law, during the transfer of organic food from
one trophic level to the next,
only about ten percent of the organic matter is stored as flesh.
The remaining is lost during transfer or broken down in respiration.
• Plants utilise sun energy for primary production and can store
only 10% of the utilised energy as net production available for
the herbivores.
• When the plants are consumed by animal, about 10% of the
energy in the food is fixed into animal flesh which is available for
next trophic level (carnivores). When a carnivore consumes that
animal, only about 10% of energy is fixed in its flesh for the
higher level.
So at each transfer 80 - 90% of potential energy is dissipated
as heat (second law of thermodynamics) where only 10 - 20%
of energy is available to the next trophic level.

12. Trophic Levels

13. Effects of Lindeman’s Efficiency
(10% Rule)
*Top predators are sensitive to changes in the energy flow
of an ecosystem.
*Cannot have more than 4 or 5 levels on a trophic
pyramid. Why?
*The amount of energy and space needed to feed
animals on a higher trophic level would be larger than the
amount of energy expended to forage for it.
*Omnivores (i.e., bears, humans, raccoons, opossums,
coyotes, etc.) can switch trophic levels depending on the
food sources that are available.
*Eating at lower trophic levels can support more
members of a population in an ecosystem.

14. ENERGY FLOW MODELS
• There is unidirectional flow of energy in an ecosystem.
• From energetics point of view ,it is essential to
understand-
1. The efficiency of the producers in the absorption and then
conversion of solar energy into chemical form of energy.
2. The use of this converted form of energy by the consumers.
3. The total assimilated energy in the form of food.
4. The loss of energy through respiration, heat, excretion.
5. Gross net production.

15. TYPES OF ENERGY FLOW MODELS
1. Universal model
2. Single channel energy flow
models
3. Y – shaped or 2- channel energy
flow model

16. 1. Universal energy flow model
• Given by E. P. Odum.
•
It explain the flow of energy through an ecosystem, where part of energy is
assimilated for the production of biomass and some part get loss due to heat or
respiration, single channel of green producers to herbivores and carnivores.
• Example: single channel energy flow model for grazing food chain is given
below:

17. Primary Production: The rate at which radiant energy is converted
into organic substances by photosynthesis or chemo-synthesis by the
primary producer.
GPP = NPP + R Secondary Production:
• The plant energy is used up for producing organic matter of the
herbivores which, in turn is used up by carnivores.
• The amount of energy stored by the herbivores or carnivores( in
excess of respiratory loss) is known as secondary production.
• In other word we can say that energy stored at consumer level for
use by the next trophic level is known as secondary production.
Net Primary Production( NPP) : Some part of the organic matter
produce during photosynthesis get used during respiration process to
produce energy for the sustenance of the primary producer, so the
amount of remaining organic matter left is known as Net primary
production (NPP=GPP-R).

18. 2. Single-Channel Energy Models:

19.  total incoming solar radiation (118,872
gcal/cm2/yr), 118,761 gcal/cm2/yr remain un-
utilised, and thus
 gross production (net production plus respiration) by autotrophs
is 111 gcal/cm2/yr with an efficiency of energy capture of 0.1 0
per cent.
 It may also be noted that 21 percent of this energy or 23
gcal/cm2/yr is consumed in metabolic reactions of autotrophs
for their growth, development, maintenance and reproduction.
 It may be seen further that 15 gcal/cm2/yr are consumed
by herbivores
 that graze or feed on Autotrophs-this amounts to 17 per cent
of net autotroph production.
•

21. • Firstly, there is one-way street along which energy moves
(unidirectional flow of energy).
• Secondly, there occurs a progressive decrease in energy level at
each trophic level from producers to herbivores and then to
carnivores.
• Thus at each transfer of energy from one level to another, major
part of energy is lost as heat or other form.
• There is a successive reduction in energy flow whether we consider
it in terms of total flow (i.e. total energy input and total
assimilation) or secondary production and respiration components.
• Thus, of the 3,000 Kcal of total light falling upon the green plants,
approximately 50 per cent (1500Kcal) is absorbed, of which only 1
per cent (15 Kcal) is converted at first trophic level.
Thus shorter the food chain, greater would be the available food
energy as with an increase in the length of food chain there is a
corresponding more loss of energy.

22. 2. Y-shaped Energy Flow Models:
 The Y-shaped model further indicates that the two food chains
namely the grazing food chain and detritus food chain are in fact,
under natural conditions, not completely isolated from one another.
 The grazing food chain beginning with green plant base going to
herbivores and the detritus food chain beginning with dead organic
matter acted by microbes, then passing to detritivores and their
consumers.
 For instance, dead bodies of small animals that were once part of
the grazing food chain become incorporated in the detritus food
chain as do the feces of grazing food animals.
 Functionally, the distinction between the two is of time lag
between the direct consumption of living plants and ultimate
utilisation of dead organic matter.
 The importance of the two food chains may differ in different
ecosystems, in some grazing is more important, in others detritus is
major pathway.

24. The important point in Y-shaped model is that the two food chains
are not isolated from each other. This Y- shaped model is more
realistic and practical working model than the single-channel
model because,
• The channels belong to either of the two basic food chains i.e.,
will be either a grazing or a detritus food chain.
• it confirms to stratified structure of ecosystems,
• it separates the grazing and detritus chains (direct
consumption of living plants and utilization of dead organic
matter respectively) in both time and space, and
• that the micro-consumers (absorptive bacteria, fungi) and the
macro-consumers (phagotrophic animals) differ greatly size-
metabolism relations. (E-P> Odum. 1983).
• Interlocking pattern of such several chains in food web of an
ecosystem would lead to a multi-channel flow of energy.