Transcript File - Riske Science

Energy and Respiration
1
Energy and food
The amount of energy available
from a certain food is sometimes
called its caloric value
The average adult requires about
8400 Kilojoules (2000 kilocalories)
of energy per day
An adult male undertaking heavy
physical labor may require as
much as 14,700 kJ (3500 kcal)
2
Energy and food
• Carbohydrates, proteins and fats make
up most of the human diet.
• The idea ratio should be approximately
60% to 30% to 10% respectively
• Carbohydrates are the most readily
available source of energy
• Fats which are essentially non-oxidized
provide the most energy per unit mass
3
Energy and food
The body does not “burn” food, but
nevertheless 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.
4
The Bomb Calorimeter
A bomb calorimeter can be
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
7
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)
= 25,086 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
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Adenosine Triphosphate
Energy released from the catabolic destruction of
carbon containing molecules is stored in ATP.
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ATP and ADP
13
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
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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
-1
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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 relatively easy for the body to get rid of the
Carbon Dioxide and excess water. This is
excretion (the removal of the toxic waste
products of metabolism),
Maximum energy is released from the glucose.
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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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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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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
21
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
is released and
exhaled.
CO2
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Hemoglobin and Oxygen
Transport Poisons
Species such as carbon monoxide and cyanide
ions poison hemoglobin
They attach to the
iron more or less
permanently, making
it impossible for the
hemoglobin to
transport carbon
dioxide or oxygen
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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+ +24e+
Fe3+ + e-  Fe2+ (Metal ion is reduced)
Reduction stage
O2 + 4H+ +4e-  2H2O
Fe2+  Fe3+ + e- (Metal ion is oxidized)
Cu+  Cu2+ + e-
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