Transcript Energy and Respiration

Energy and Respiration
Larry Scheffler
Lincoln High School
2009-2010
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Energy and food
The amount of energy available from a certain food
is sometimes called its calorific value
The average adult requires about 8400 Kilojoules
(2000 kcal) of energy per day
An adult male undertaking heavy physical labor may
require as much as 14,700 kilojoules (3500 kcal)
Carbohydrates, proteins and fats make up most of
the human diet
Carbohydrates are the most readily available source
Fats which are non-oxidized provide the most energy
per mass
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Energy and food
The body does not burn food but never the
less it is converted to the same set of
products (CO2 and H2O) through a series of
oxidation reactions.
Since Hess’ law shows that the energy
change is independent of the pathway, the
same amount of energy is released through
burning food.
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The Bomb Calorimeter
A bomb calorimeter is often
used to measure the
energy content of food.
The calorific value of food
can be measured by heating
a pre-measured mass of
food and igniting it in an
oxygen atmosphere.
The heat is transferred to a
water system and the heat
evolved is computed from
the temperature change and
the mass of water.
A diagram of a bomb calorimeter
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The Bomb Calorimeter
The calorific value of a
candy bar is about 250
Dietician’s Calories or 250
kilocalories)
This means that if it were
burned in a calorimeter, the
energy produced on
combustion would raise the
temperature of 2.5 kg water
by 100°C assuming that the
calorimeter itself does not
absorb any energy.
In most cases the energy
absorbed by the calorimeter
cannot be ignored and must
be included in the
calculations.
A diagram of a bomb calorimeter
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The Bomb Calorimeter
A large candy bar
weighs 50 g. If a 5.00 g
sample of the candy
bar, on complete
combustion raises the
temperature of 500 g
water in a glass
container by 59.6°C.
Calculate the calorific
value of the candy bar.
The heat capacity of
the glass calorimeter is
20.9 cal °C-1
A diagram of a bomb calorimeter
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The Bomb Calorimeter
A large candy bar weighs 50 g. If a 5.00 g sample of the
candy bar, on complete combustion raises the
temperature of 500 g water in a glass container by 59.6°C,
calculate the calorific value of the candy bar. The heat
capacity of the glass calorimeter is 20.9 cal °C-1
Heat produced = heat absorbed by water + heat
absorbed by calorimeter
= (m x C x ΔT)water + (m x C. x ΔT)calorimeter
= (500 g x 1.00 cal g-1 °C-1 x 59.6 °C) +
(20.9 cal °C-1 x 59.6°C)
= 25086 calories
= 25.09 kcal (produced by 5.0 g of candy bar)
= 5.02 kcal g-1
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Respiration
Respiration is crucial function for all
living organisms.
In general the process of respiration
serves two basic purposes
1. the disposal of electrons generated
during catabolism
2. the production of ATP.
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Cellular Respiration
Cellular respiration involves a set of
metabolic processes that occur in the cell
to convert biochemical energy from
nutrients into adenosine triphosphate
(ATP) and waste products
Respiration involves catabolic redox
reactions. One molecule is oxidized and
another is reduced.
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Adenosine Triphosphate
The structure of ATP includes an adenine group, a
ribose sugar, and three phosphate groups
Adenosine Triphosphate
Energy released from the catabolic destruction of
carbon containing molecules is stored in ATP.
ATP and ADP
Energy is released
when a phosphate
group is released
from ATP resulting in
the formation of
ADP. The
reversible reaction
between ATP and
ADP acts much like
a “battery “allowing
the cell to store and
release energy
The conversion of ATP to ADP releases about 30.5 kJ mol-1
Aerobic and Anaerobic
Respiration
Respiration may be either aerobic or
anaerobic
Aerobic respiration uses oxygen as its
terminal electron acceptor,
Anaerobic respiration uses terminal
electron acceptors other than oxygen
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Aerobic Respiration
Aerobic respiration requires oxygen
A. It involves the break down of glucose,
amino acids and fatty acids to release
energy.
B. Oxygen is the terminal electron acceptor.
C. The overall process of aerobic respiration
can be described as:
Glucose + Oxygen →Energy + Carbon dioxide +
Water
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Aerobic Respiration
The aerobic respiration is a high energy
yielding process.
Up to 38 molecules of ATP are produced for
every molecule of glucose that is utilized.
Aerobic respiration takes place in almost all
living things.
It is easy to get rid of the Carbon Dioxide and
excess water; this is excretion (the removal
of the toxic waste products of metabolism),
and maximum energy is released from the
glucose.
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Anaerobic Respiration
Anaerobic respiration is a special type of respiration,
which takes place without oxygen to produce energy in
the form of ATP or adenosine tri-phosphate.
The process of anaerobic respiration for production of
energy can occur in either of the ways represented
below:
Glucose →Energy (ATP) + Ethanol + Carbon dioxide
(CO2)
Glucose →Energy (ATP) + Lactic acid
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Anaerobic Respiration
The process of anaerobic respiration is relatively
less energy yielding than aerobic respiration
During the alcoholic fermentation or the anaerobic
respiration two molecules of ATP (energy) are
produced. for every molecule of glucose used in the
reaction.
Likewise for lactate fermentation 2 molecules of ATP
are produced for every molecule of glucose used.
Thus anaerobic respiration breaks down one
glucose molecule to obtain two units of the energy
storing ATP molecules.
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Anaerobic Respiration
Some organisms can respire in the absence of air: this
is anaerobic respiration. This does not release so much
energy and it produces more toxic waste products.
When Oxygen is not available, anaerobic respiration
also occurs in humans.
Anaerobic respiration can take place during vigorous
exercise, building up lactic acid in muscle tissue. This
results in muscle pain and cramping.
The bacteria in milk also produce lactic acid but is an
optical isomer of that produced in muscle cramping.
Yeasts produce alcohol which is also toxic. Eventually
there will be so much alcohol that the yeast cannot
survive.
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Hemoglobin and Oxygen
Transport
The ability of iron to form complexes plays an important in
the transport of oxygen and carbon dioxide in the
hemoglobin of the blood
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Hemoglobin and Oxygen
Transport
Hemoglobin is a complex protein. At certain sites within the
protein are structures known as porphyrin rings. A Fe2+ ion
at the center of the ring attracts and transports oxygen
At high oxygen
concentrations
(as in the lungs)
hemoglobin
binds to the
oxygen
molecules which
is then carried to
the cells.
O2
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Hemoglobin and Oxygen
Transport
At high Carbon dioxide concentrations as are
found at the cell level hemoglobin
binds to the
carbon dioxide
molecules
which are then
transported
back to the
lungs where the
carbon dioxide
CO2
is exhaled
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Hemoglobin and Oxygen
Transport
Species such as carbon monoxide and Cyanide
poison hemoglobin
They attach to
the iron more or
less
permanently,
rendering the
hemoglobin
useless
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Electron Transport
The oxidation of food at the
cellular level involves a
series of redox reactions
involving electron transport
These reactions take place
+
in the mitochondria found
inside the cell
The enzymes that catalyze
these oxidation processes
are called cytochromes
Cytochromes incorporate
porphyrin rings with either a
Cu2+ or Fe2+ at the center
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Electron Transport
The cytochrome structure heme group from Cytochrome
oxidase
Cytochromes contain Cu2+
or Fe3+ ions. The porphyrin
ligand contains 4 nitrogen
atoms, each of which
donates 2 electrons.
+
During each step of the
oxidation of glucose:
Fe3+  Fe2+ + eor
Cu2+  Cu+ + e-
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Electron Transport
The cytochrome structure heme group from
Cytochrome oxidase.
Oxidation stage of glucose
C6H12O6 + 6H2O  6CO2+24H+ +24eFe3+ + e-  Fe2+
+
(Metal ion is reduced)
Reduction stage
O2 + 4H+ +4e-  2H2O
Fe2+  Fe3+ + eCu+  Cu2+ + e-
(Metal ion is oxidized)
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