ENVI 3 energy flow in an ecosystem

1. Energy Flow in an
Ecosystem
Chapter 3

2. Trophic Levels
 Used to locate the position or level of an
organism during its energy-seeking
activities.
 Plants are said to belong to the first trophic
level since the chemical energy they both
store and utilize is one step from the
original solar energy they trap.

3. Four Major Trophic Levels
 Primary producers (plants, algae, bacteria)
 Primary consumers (herbivores)
 Secondary consumers (carnivores)
 Tertiary consumers (detritivores)

6. Basic Photosynthesis

7. Cellular Respiration
 Converts sugar into energy, adenosine
triphosphate (ATP)

8. Food Chain
 a linear network of links in a food web starting from
producer organisms (such as grass or trees which use
radiation from the sun to make their food) and ending
at apex predator species (like grizzly bears or killer
whales), detritivores (like earthworms or woodlice), or
decomposer species (such as fungi or bacteria).

9. Two Basic Types of Food Chain
A. Grazer Food Chain
 Starts with green plants which are the producers. The
producers are grazed by the herbivores which are
further eaten by carnivores.
B. Detritus Food Chain
 Starts with dead organic matter which is eaten by other
animals in the soil. A large amount of energy flows
through the detritus food chain, ultimately the organic
matter is decomposed

10. Two Basic Types of Food Chain
A. Grazer Food Chain
 Starts with green plants which are the producers. The
producers are grazed by the herbivores which are
further eaten by carnivores.
B. Detritus Food Chain
 Starts with dead organic matter which is eaten by other
animals in the soil. A large amount of energy flows
through the detritus food chain, ultimately the organic
matter is decomposed

13. Food Chain
 is a series of
interconnected food
chain

15. Pyramid of Energy
 An energy pyramid’s shape shows
how the amount of useful energy
that enters each level — chemical
energy in the form of food —
decreases as it is used by the
organisms in that level.
 The consequence is that even
though a lot of energy may be
taken in at any level, the energy
that ends up being stored there –
which is the food available to the
next level — is far less. Scientists
have calculated that an average of
90% of the energy entering each
step of the food chain is “lost” this
way.

16. Pyramid of Biomass
Biomass means the dry mass of living
material at a stage in a food chain. The
biomass goes down as you go from one
stage to the next, just like the amount of
energy.
 A pyramid of biomass is a chart, drawn
to scale, showing the biomass at each
stage in a food chain. The bars become
narrower as you reach the top.

17. Pyramid of Biomass
Each stage in a food chain or pyramid
of biomass is called a trophic level. It
can be difficult to make a pyramid of
biomass because:
 there may be problems measuring
dry biomass
 an organism may belong to more
than one trophic level, so it cannot
easily be represented by one bar.

18. Thermodynamics
 Traditionally been called the law of conservation of energy
 states that energy can be transformed from one form to
another, but it cannot be created or destroyed. This law
suggests that all energy transfers, gains, and losses within a
food web can be accounted for in an energy budget.
First Law of Thermodynamics
 refers to the use of heat as a convenient measurement of
chemical energy in any reaction

19.  states that whenever energy is
transformed, some of must be
degraded into a less useful form.
 In ecosystems, the biggest losses
occur as heat.
 explains why energy transfers are
never 100% efficient. In fact,
ecological efficiency, which is the
amount of energy transferred from
one trophic level to the next, ranges
from 5-30%. On average, ecological
efficiency is only about 10%.
Second Law of Thermodynamics

20. Calculating Energy Efficiency
 This bullock has eaten 100 kJ of
stored energy in the form of grass,
and excreted 63 kJ in the form of
faeces, urine and gas. The energy
stored in its body tissues is 4 kJ and
33 kJ has been used up in respiration.
 Only 4 kJ of the original energy
available to the bullock is available to
the next stage, which might be
humans. The efficiency of this energy
transfer is:
 efficiency = 4 ÷ 100 × 100 = 4%