Food Chains &
Thermodynamics
Goal
• To develop an understanding of the
interdependence of all organisms and the
need for conserving natural resources
Concept
• Concept: Living organisms share in a
variety of complex interrelationships
which are based on interdependence.
• Concept Objective: To understand that
energy does not cycle within an
ecosystem
Energy changes in the
ecosystem
A. First law of thermodynamics
B. Second law of thermodynamics
1st Law of Thermodynamics
• Rub hands together
• Place on face
• What happened?
1st Law of Thermodynamics
• The First Law of Thermodynamics states that
energy cannot be created or destroyed but only
changes forms.
• In the introductory activity chemical energy in
our bodies was changed to mechanical energy
in our arms.
– Friction caused some of this mechanical energy to
be changed to noticeable heat energy in our hands.
– We also felt some of the heat move to our cooler
faces.
1st Law of Thermodynamics
• The First Law of Thermodynamics states that
energy cannot be created or destroyed but only
changes forms.
• A practical ecological consequence of this law
is that all living things must have a source of
energy.
• The ultimate source of energy for most living
things is the sun.
2nd Law of
Thermodynamics
• The Second Law of Thermodynamics
states that at every energy transfer some
portion of the available energy is
degraded to heat which moves to cooler
objects.
• We felt the heat in our hands move to our
cooler face.
2nd Law of
Thermodynamics
http://www.epa.gov/mercury/exposure.htm
•
•
Producers are the only organisms that are able to take the radiant energy
from the sun and change it to chemical energy in food, glucose sugar.
In the process of photosynthesis producers use carbon dioxide and water,
in the presence of chlorophyll and light, to make sugar and oxygen.
– In the "light" phase of photosynthesis energy-rich adenosine triphosphate (ATP)
molecules are formed.
– In "dark" phase a variety of substances required to build and maintain tissues
are produced.
– Plants may convert as much as 75 percent of the light received into chemical
energy in glucose sugar.
•
•
Organisms in the environment have very poor efficiency in converting the
energy they receive into usable energy or into energy which is stored and
eaten by the next link on a food chain.
• On average vertebrates use
about 98% of assimilated
energy for metabolism, leaving
only 2% for growth and
reproduction. This is largely
because they are regulating
their temperature
• On average, invertebrates use
only ~80% of assimilated energy
for metabolism, and thus exhibit
greater net production efficiency
(~20%) than do vertebrates.
• Plants have the greatest net
production efficiencies, which
range from 30-85%.
http://www.globalchange.umich.edu/globalchange1/current/lectures/kling/highertrophic/trophic2.html#transfer
•
•
•
•
300 trout are needed to support one man for a year.
The trout, in turn, must consume 90,000 frogs,
that must consume 27 million grasshoppers
that live off of 1,000 tons of grass.
-- G. Tyler Miller, Jr., American Chemist (1971)
• Only a fraction of the energy available at one trophic
level is transferred to the next trophic level. (which law
of thermodynamics is this?) The rule of thumb is 10%,
but this is very approximate.
• Typically the numbers and biomass of organisms
decrease as one ascends the food chain.
REVIEW
1. Can energy be created or destroyed?
2. This is a statement of what law?
3. Which living things are able to convert
radiant or solar energy into usable
chemical energy?
4. As food moves through an ecosystem is
all the energy converted into usable
energy?
5. This is a statement of what law?
REVIEW
• 1. Can energy be created or destroyed? (No)
• 2. This is a statement of what law? (First Law of
Thermodynamics)
• 3. Which living things are able to convert
radiant or solar energy into usable chemical
energy? (Producers or plants)
• 4. As food moves through an ecosystem is all
the energy converted into usable energy? (No)
• 5. This is a statement of what law? (Second
Law of Thermodynamics)
Radiant energy to chemical
energy
A. Photosynthesis
6H2O + 6CO2 ----------> C6H12O6+ 6O2
•
•
Light phase: solar energy is harvested and transferred into the chemical bonds of ATP; can
occur only in light.
In a series of reactions the energy is converted (along an electron transport process) into
ATP and NADPH.
Water is split in the process, releasing oxygen as a by-product of the reaction.
http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookPS.html
Radiant energy to chemical
energy
Dark phase:
carbon dioxide
from the
atmosphere (or
water for
aquatic/marine
organisms) is
captured and
modified by the
addition of
Hydrogen to form
carbohydrates
http://web.mit.edu/esgbio/www/ps/dark.html
Radiant energy to chemical
energy
B. Energy conversions happened with:
• Phosphorylation
• Oxidation-reduction reactions
http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookPS.html
Release of energy
A.
•
•
•
Movement of energy to other organisms
Energy moves through the ecosystem as consumers eat and as
decomposers decay other organisms.
The energy stored in glucose may be released when organisms
burn food in their cells during respiration. (Note: respiration
occurs in the cells of producers, consumers, and decomposers.)
These energy releasing reactions usually occur in the cell
mitochondria.
Oxygen is combined with glucose forming water and carbon
dioxide with the release of energy. This is just opposite of the
photosynthesis reaction.
For example: exercise vigorously for a few minutes. Observe the rapid
breathing, increased heart rate, skin changes, and other
evidence of increased respiration
Release of energy
1.
2.
In the cytoplasm is glycolysis
In the mitochondria is cellular
respiration
Under aerobic conditions there are
2 reactions the Kreb’s cycle and
electron transport
•
–
–
–
In the Kreb’s cycle the small chain
carbons are completely oxidized
and a small amount of energy is the
result (ATP, NADH)
Electron transport is where more
energy in the form of ATP is
produced through oxidative
phosphorylation
Note: oxidation-reduction reactions
are a reaction in which electrons
are transferred from a donor (the
reducing agent) to an acceptor
molecule (the oxidizing agent).
image is from http://www.biosci.uga.edu/almanac/bio_104/notes/jun_4.html.
Release of energy
B. Power for life processes
• The energy released by respiration is
used to power the life processes of
organisms including:
– movement, growth, chemical synthesis,
movement of materials in the organism,
reproduction, and others.
•
Much of the energy released in
respiration is lost to the environment as
heat.
Loss of chemical energy
A.
Use of energy by organisms: Energy moves through
the ecosystem as consumers eat and as
decomposers decay other organisms.
B.
Loss of heat energy: Much of the energy released in
respiration is lost to the environment as heat.
The energy stored in glucose may be released when
organisms burn food in their cells during respiration.
•
–
•
(Note: Respiration occurs in the cells of producers,
consumers, and decomposers.)
These energy releasing reactions usually occur in the
cell mitochondria.
C. Stored Energy – next slide
Loss of chemical energy
C. Stored energy (glucose)
1. There are in general many more
producers
2. Limiting numbers on a pyramid because
of the loss of stored energy as you
move up the food chain.
In Summary
• The energy released by respiration is
used to power the life processes of
organisms including movement, growth,
chemical synthesis, movement of
materials in the organism, reproduction,
and others.
Review
1. What happens to the amount of energy
available as you move to higher levels
on a food pyramid?
2. On the average, it decreases how many
times as you move up one level?
3. How many times would the energy
decrease if you moved up two levels?,
three levels?, four levels?
Review
1. What happens to the amount of energy
available as you move to higher levels
on a food pyramid? (It decreases)
2. On the average, it decreases how many
times as you move up one level? (10)
3. How many times would the energy
decrease if you moved up two levels?
(100), three levels? (1000), four levels?
(10,000)