Cellular Respiration in Plants
Cellular respiration, also referred to as oxidative
metabolism, is a set of important metabolic reactions in which biochemical
energy, derived from nutrients, is converted into useful energy (exergonic
reaction), thereby releasing waste products. The energy is released in the form
of adenosine triphosphate (ATP). This energy is then utilized for driving other
processes including photosynthesis and transportation of molecules across cell
membranes. Cellular respiration is also a catabolic reaction, in the sense that
it facilitates the oxidation of one molecule while reducing the other. There
are four primary stages of cellular respiration in plants: glycolysis,
transition reaction, Krebs cycle, and electron transport chain (ETC).
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Glycolysis in plants |
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ATP |
Transition
Reaction
Transition reaction, also referred to as pyruvate decarboxylation is an important intermediary step in the process of cellular respiration as it forms a connecting link between the metabolic pathways of glycolysis and Kreb’s cycle. In this phase, pyruvate from glycolysis gets decarboxylated and reacts with Coenzyme A to form Acetyl CoA.
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Pyruvate decarboxylation in Plants |
It is also known as Citric acid cycle or the tricarboxylic acid cycle. Kreb’s cycle is a series of 8 steps which oxidize Acetyl CoA to CO2 while NAD gets reduced to NADH (it is further used in the ETC to liberate ATP). This cycle takes place in the mitochondrial matrix in the presence of oxygen. For complete oxidation of one glucose molecule, 2 molecules of acetyl coA should enter the Kreb’s cycle to release 4 CO2, 6 NADH, 2 ATP and 2 FADH2 molecules (another type of energy-rich molecules).
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ETC in Plants |
Electron Transport Chain (ETC)
ETC or oxidative phosphorylation is the last stage
of cellular respiration in plants. Most of the energy is released by the
electron transport chain (remaining 32-34 ATP molecules). ETC takes place in the
inner membrane of mitochondria and comprises of a chain of electron-carrying
proteins. Electrons are thus transferred from one protein to the other, until
they reach the final electron acceptor, oxygen. Protons are also added to
oxygen leading to the formation of water, but no ATP. ATP is produced by a
proton motive force which is a source of stored potential energy. This
potential energy (chemiosmotic potential) is generated as a result of gradient
that is formed when the protons (hydrogen) move across the biological membrane.
Therefore, ETC triggers a gradient that helps in the formation of ATP (this
process is known as chemiosmosis).
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