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breaking the chemical bonds of glucose molecules. Thus cellular respiration is the essential
processes of life. So living cells must carry out cellular respiration. It can be in the presence
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of oxygen that is ‘aerobic respiration’, or in the absence of oxygen as in bacterial respiration
by anaerobic method which is called fermentation. The substances become sour because
of ethyl alchohol or lactic acid is produced in this process. In Animals the anaerobic
respiration leads to formation of lactic acid from glucose. In anaerobic repiration few ATP
molecules are produced. Cellular respiration in prokaryotic cells like that of bacteria occurs
within the cytoplasm. In eukaryotic cells cytoplasm and mitochondria are the sites of the
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reactions. The produced energy is stored in mitochondria in the form of ATP. That is why
mitochondria are called “power houses of the cell”.
The exact chemical details of the breakdown of sugar or other foods within a living cell
does not take place as a single reaction, but occurs in a series of small steps.
How does this affect the energy release? As the change in the chemical nature of the
molecule from one stage to the next is slight, in any step small amount of energy is released.
The complete breakdown of a sugar molecule with the release of all its available energy
Free distribution by T.S. Government 2019-20 33
involves a series of different chemical reactions.
outer membrane
inner membrane
From the breakdown of glucose the energy is
released and stored up in a special compound, known
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A
cristae as ATP (adenosine triphosphate). It is a small parcel of
matrix chemical energy. The energy currency of these cells
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AN
is ATP an energy rich compound that is capable of
supplying energy wherever needed within the cell. Each
ATP molecule gives 7200 calories of energy. This
energy is stored in the form of phosphate bonds. If the
fig-10: Mitochondria
bond is broken the stored energy is released.
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Do cells of alveoli or lungs also require oxygen to carry out cellular
respiration? Why/Why not?
In short, at cellular level we could have the following pathways starting
with glucose (It is one example, remember that there are other components
of food as well).
LA
Lactic acid + Energy
Absence or low
Eg: Lactobocilus
amount of oxygen
(anaerobic respiraton
and fermentation) Ethanol + CO2+ Energy
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Glucose Pyruvate Eg: Yeast
(3 carbon compound)
+ Energy
(Glycolysis)
Presence of Oxygen CO2 + H2O + Energy
(aerobic respiration) Eg: Plants and animals
T
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Glucose is the most commonly used sugar for deriving energy in plants,
animals and in microorganisms. In all these organisms the glucose is
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oxidized in two stages. In the first stage it is converted into two molecules
of pyruvic acid. In the second stage if oxygen is available pyruvic acid is
oxidized to CO2, water and large amount of energy is released.
If oxygen is inadequate or not utilised pyruvic acid is converted into
either ethanol or lactic acid and very little amount of energy (nearly one
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tenth of that is produced with adequate amount of oxygen) is released.
Can energy be released without oxygen?
After undergoing strenous exercise, we feel pain in muscles. Does
adequate oxygen reach the muscles?
What is being formed in the muscles?
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