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Energy and Respiration
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Energy and foodThe amount of energy available from acertain food is sometimes called itscalorific value
The average adult requires about 8400Kilojoules (2000 kcal) of energy per day
An adult male undertaking heavy physicallabor may require as much as 14,700kilojoules (3500 kcal)
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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 non-oxidized provide the most energy per mass
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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 oxidationreactions.
Since Hess law shows that the
energy change is independent of the
pathway, the same amount of energyis released through burningfood.
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The Bomb Calorimeter
The calorific value of acandy bar is about 250Dieticians Calories or 250kilocalories)
This means that if it were
burned in a calorimeter, theenergy produced oncombustion would raise thetemperature of 2.5 kg waterby 100C assuming that thecalorimeter itself does not
absorb any energy.In most cases the energyabsorbed by the calorimetercannot be ignored and mustbe included in the
calculations.
A diagram of a bomb calorimeter
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The Bomb Calorimeter
A bomb calorimeter is oftenused to measure theenergy content of food.
The calorific value of foodcan be measured by heating
a pre-measured mass offood and igniting it in anoxygen atmosphere.
The heat is transferred to awater system and the heatevolved is computed fromthe temperature change andthe mass of water
A diagram of a bomb calorimeter
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The Bomb CalorimeterA large candy bar
weighs 50 g. If a 5.00 gsample of the candybar, on completecombustion raises thetemperature of 500 g
water in a glasscontainer by 59.6C.
Calculate the calorificvalue of the candy bar.
The heat capacity ofthe glass calorimeter is20.9 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 thecandy bar, on complete combustion raises thetemperature of 500 g water in a glass container by 59.6C,calculate the calorific value of the candy bar. The heatcapacity of the glass calorimeter is 20.9 cal C-1
Heat produced = heat absorbed by water + heat
absorbed by calorimeter
= (m x C x T)water+ (m x C. x T)calorimeter
= (500 g x 1.00 cal g-1
C-1
x 59.6 C) +(20.9 cal C-1 x 59.6C)
= 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 crucialfunction for all livingorganisms.
In general theprocess ofrespiration servestwo basic purposes1. The disposal of
electrons generatedduring catabolism
2. The production ofATP.
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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 intoadenosine triphosphate
(ATP) and waste products
Respiration involves
catabolic redoxreactions. 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
Energy is releasedwhen a phosphategroup is releasedfrom ATP resultingin the formation of
ADP. Thereversible reactionbetween ATP and
ADP acts much likea battery allowingthe cell to store andrelease energy
The conversion of ATP to ADP releases about 30.5 kJ mol-1
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Aerobic and Anaerobic Respiration
Respiration may be eitheraerobic 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 yieldingprocess.
Up to 38 molecules of ATP are produced for
every molecule of glucose that is utilized.Aerobic respiration takes place in almost allliving things.
It is easy to get rid of the Carbon Dioxide and
excess water; this is excretion (the removal ofthe toxic waste products of metabolism), andmaximum energy is released from the glucose.
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Anaerobic Respiration
Some organisms can respire in the absence of air: this isanaerobic respiration. This does not release so muchenergy and it produces more toxic waste products.
When Oxygen is not available, anaerobic respiration also
occurs in humans.Anaerobic respiration can take place during vigorousexercise, building up lactic acid in muscle tissue. Thisresults in muscle pain and cramping.
The bacteria in milk also produce lactic acid but is an opticalisomer of that produced in muscle cramping.
Yeasts produce alcohol which is also toxic. Eventually therewill be so much alcohol that the yeast cannot survive.
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Anaerobic Respiration
Anaerobic respiration is a special type of respiration, whichtakes 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 isrelatively less energy yielding than aerobicrespiration
During the alcoholic fermentation or the
anaerobic respiration two molecules of ATP(energy) are produced. for every molecule ofglucose used in the reaction.
Likewise for lactate fermentation 2 molecules of
ATP are produced for every molecule ofglucose used.
Thus anaerobic respiration breaks down oneglucose molecule to obtain two units of the
energy storing ATP molecules. 1
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Hemoglobin and Oxygen Transport
The ability of iron to form complexes plays an important inthe transport of oxygen and carbon dioxide in thehemoglobin of the blood
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Hemoglobin and Oxygen Transport
Hemoglobin is a complex protein. At certain sites within theprotein are structures known as porphyrin rings. A Fe2+ ionat the center of the ring attracts and transports oxygen
O2
At high oxygen
concentrations
(as in the lungs)
hemoglobin
binds to the
oxygen
molecules whichis then carried to
the cells.
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Hemoglobin and Oxygen Transport
At high carbon dioxide concentrations as arefound at the cell level hemoglobin
CO2
binds to the
carbon dioxide
moleculeswhich are then
transported
back to the
lungs where the
carbon dioxide
is exhaled
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Hemoglobin and Oxygen Transport
They attach to
the iron more orless
permanently,
rendering the
hemoglobinuseless
Species such as carbon monoxide and Cyanidepoison hemoglobin
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Electron Transport
The oxidation of food at thecellular level involves aseries of redox reactionsinvolving electron transport
These reactions take placein the mitochondria foundinside the cell
The enzymes that catalyzethese oxidation processes
are called cytochromesCytochromes incorporateporphyrin rings with either aCu2+ or Fe2+ at the center
+
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Electron Transport
The cytochrome structure heme group from cytochromeoxidase
+
Cytochromes contain Cu2+
or Fe3+ ions. The porphyrin
ligand contains 4 nitrogenatoms, each of which
donates 2 electrons.
During each step of theoxidation of glucose:
Fe3+ Fe2+ + e-
or
Cu2+ Cu+ + e-
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Electron Transport
The cytochrome structure heme group fromcytochrome oxidase.
+
Oxidation stage of glucose
C6H
12O
6+ 6H
2O 6CO
2+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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