Cellular Respiration | NMDCAT 2021 | Fermentation
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- Опубліковано 8 жов 2024
- About This Video!
Biological oxidation The maintenance of living system requires a continual supply of free energy
which is ultimately derived from various oxidation reduction reactions. Except for photosynthetic
and some bacterial chemosynthetic processes, which are themselves oxidation reduction reactions,
all other cells depend ultimately for their supply of free energy on oxidation reactions in respiratory
processes. In some cases biological oxidation involves the removal of hydrogen, a reaction catalyzed
by the dehydrogenases linked to speciic coenzymes. Cellular respiration is essentially an oxidation
process.
Cellular Respiration
Cellular respiration may be sub-divided into 4 stages:
i. Glycolysis ii. Pyruvic acid oxidation
iii. Krebs cycle or citric acid cycle iv. Respiratory chain
Out of these stages the irst occurs in the cytosol for which oxygen is not essential, while the other
three occur within the mitochondria where the presence of oxygen is essential.
RESPIRATION
Living organisms need energy to carry on their vital activities. This energy is provided from within
the cells by the phenomenon of respiration. Respiration is the universal process by which organisms
breakdown complex compounds containing carbon in a way that allows the cells to harvest a
maximum of usable energy.
In biology the term respiration is used in two ways. More familiarly the term respiration means
the exchange of respiratory gases (CO2 and O2
) between the organism and its environment. This
exchange is called external respiration. The cellular respiration is the process by which energy is
made available to cells in a step by step breakdown of C-chain molecules in the cells.
Aerobic and Anaerobic Respiration
The most common fuel used by the cell to provide energy by cellular respiration is glucose,. The way
glucose is metabolized depends on the availability of oxygen. Prior to entering a mitochondrion,
the glucose molecule is split to form two molecules of pyruvic acid. This reaction is called glycolysis
(glycolysis literally means splitting of sugar), and occurs in the cytosol and is represented by the
equation:
This reaction occurs in all the cells and biologists believe that an identical reaction may have occurred
in the irst cell that was organized on earth.
The next step in cellular respiration varies depending on the type of the cell and the prevailing
conditions
Cell processes pyruvic acid in three major ways, alcoholic fermentation, lactic acid fermentation
and aerobic respiration. The irst two reactions occur in the absence of oxygen and are referred
to as anaerobic (without oxygen). The complete breakdown of glucose molecule occurs only in the
presence of oxygen, i.e. in aerobic respiration. During aerobic respiration glucose is oxidized to CO2
and water and energy is released.
Anaerobic Respiration
(i) Alcoholic Fermentation: In primitive cells and in some eukaryotic cells such as yeast,
pyruvic acid is further broken down by alcoholic fermentation into alcohol (C2
H5
OH) and CO2.
(ii) Lactic acid fermentation: In lactic acid fermentation, each pyruvic acid molecule is
converted into lactic acid C3
H6
O3
in the absence of oxygen gas:
This form of anaerobic respiration occurs in muscle cells of humans and other animals during
extreme physical activities, such as sprinting, when oxygen cannot be transported to the cells as
rapidly as it is needed.
Both alcoholic and lactic acid fermentations yield relatively small amounts of energy from glucose
molecule. Only about 2% of the energy present within the chemical bonds of glucose is converted
into adenosine triphosphate (ATP).
Aerobic respiration (Discussed in detail under cellular respiration).
Role of mitochondria in respiration Mitochondria are large granular or ilamentous organelles
that are distributed throughout the cytoplasm of animal and plant cells. Each mitochondrion is
constructed of an outer enclosing membrane and an inner membrane with elaborate folds or
cristae that extend into the interior of the organelle.
Mitochondria play a part in cellular respiration by transferring the energy of the organic molecules
to the chemical bonds of ATP. A large “battery” of enzymes and coenzymes slowly release energy
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