The document summarizes various aspects of cellular respiration in plants. It discusses cellular respiration, where glucose and other molecules are broken down to release energy stored as ATP. It also describes the different pathways of respiration - glycolysis, the Krebs cycle, and the electron transport system. The final stages of aerobic and anaerobic respiration are compared, noting that aerobic respiration fully breaks down glucose to carbon dioxide and water, yielding more ATP. The roles of fermentation, the fate of pyruvic acid, and the amphibolic nature of respiration are also summarized.

1. RESPIRATION IN
PLANTS
By Usha.p.Rao

2. Cellular respiration
The process of breaking the c-c bonds of complex
compounds through oxidation within cell to release energy
that is stored in the form of ATP is called cellular respiration.
 The compounds that are oxidised during cellular
respiration are called respiratory substrates.
 ATP is called energy currency of the cell because
energy produced during cellular respiration is not
directly utilized instead stored in the form of ATP
later utilized in various energy requiring processes.
 The metabolites produced during cellular respiration
are used as precursors for biosynthesis of other
molecules in a cell.

3. Gaseous exchange in plants
◦ In plants each part take care of its own gas exchange needs and here the transport of gases from
one part to another takes place only a little amount.
◦ In parts of the plants, rate of respiration is very lower than animals.
◦ In plants photosynthesis results in the production of oxygen which can be used within the cell
and neighboring cells .
◦ Cell to cell movement is very simple as they are close and connected to each other.
◦ In case of woody stems and roots gaseous exchange is achieved through lenticels.
◦ Most of the parts of the plants are always in connection with air one or the other way so that
gaseous exchange takes place easily

4. Oxidation of glucose
◦ The complete combustion of glucose, which produces CO2 and H2O as end products, yields energy most of
which is given out as heat.
◦ C6H12O6+6O2 6O2+6H2O+ENERGY
◦ oxidation of glucose is not a one step but it takes place in several small steps enabling some steps to be just
large enough such that the energy released can be coupled to ATP synthesis.
◦ Oxidation requires oxygen in most of the cells, but we know there are organisms that can live without
oxygen i.e anaerobic and some are facultative anaerobes, so during complete breakdown of glucose there may
be some step where partial degradation that takes place without oxygen and that is glycolysis.
◦ Glycolysis is the process in which glucose is broken down into pyruvic acid(3c molecule)

5. Glycolysis-The term glycolysis has originated from the Greek words,
glycos for sugar, and lysis for splitting.
◦ (Embden,Mayerhof and Paranas pathway-EMP , common respiratory pathway,
cytoplasmic respiration) • In this there is degradation of glucose(6 C) to pyruvic
acid(3 C) without utilizing oxygen. • It takes place in the cytoplasm of the cell and
is common to aerobic and anaerobic respiration.
◦ In plants, the glucose is derived from sucrose, which is the end product of
photosynthesis, or from storage Sucrose is converted into glucose and fructose by
the enzyme, invertase, and these two monosaccharides readily enter the glycolytic
pathway.

6. Steps of glycolytic pathway
◦ Glucose and fructose are phosphorylated to give rise to glucose-6- phosphate, catalysed by
hexokinase. This phosphorylated form of glucose is then isomerizes to produce fructose-6-
phosphate.
◦ ATP utilized at two steps: First in the conversion of glucose into glucose-6-phosphate Second in fructose-6-
phosphate→fructose 1, 6-diphosphate. The fructose-1, 6-diphosphate is split into dihydroxyacetone
phosphate and 3-phosphoglyceraldehyde (DPGA).
◦ In one step where NADH + H+ is formed form NAD+ ; this is when 3phosphogleceraldehyde (PGAL) is
converted into 1, 3- bisphophoglyceric acid (DPGA). The conversion of 1, 3-bisphophoglyceric acid into 3-
phosphoglyceric acid is also an energy yielding process; this energy is trapped by the formation of ATP.
◦ Another ATP synthesized when phosphoenolpyruvate is converted into pyruvic acid. During this process 4
molecules of ATP are produced while 2 molecules of ATP are utilized. Thus net gain of ATP is of 2
molecules

7. Fate of pyruvic acid
◦ There are three major ways in which different cells handle pyruvic acid produced
by glycolysis.
◦ These are lactic acid fermentation, alcoholic fermentation and aerobic respiration.
◦ Fermentation takes place under anaerobic conditions in many prokaryotes and
unicellular eukaryotes.
◦ For the complete oxidation of glucose to CO2 and H2O, however, organisms
adopt Krebs’ cycle which is also called as aerobic respiration. This requires O2
supply.

8. fermentation
◦ Alcoholic fermentation-The incomplete oxidation of glucose is achieved under anaerobic
conditions by sets of reactions where pyruvic acid is converted into CO2 and ethanol.
◦ The enzyme pyruvicacid decarboxylase and alcohol dehydrogenase catalyze these
reactions. NADH + H+ is reoxidised into NAD+ .eg-yeast
◦ Lactic acid fermentation-The incomplete oxidation of glucose is achieved under
anaerobic conditions by sets of reactions where pyruvic acid is converted into CO2 and
lactic acid.
◦ organisms like some bacteria produce lactic acid from pyruvic acid. In animal cells also,
like muscles during exercise, when oxygen is inadequate for cellular respiration pyruvic
acid is reduced to lactic acid by lactate dehydrogenase. The reducing agent is
NADH+H+ which is reoxidised to NAD+ in both the processes.

9. Aerobic respiration
◦ aerobic respiration to take place within the mitochondria.
◦ the final product of glycolysis, pyruvate is transported from the cytoplasm into the mitochondria. The crucial events in aerobic
respiration are: • The complete oxidation of pyruvate by the stepwise removal of all the hydrogen atoms, leaving three molecules
of CO2 . • The passing on of the electrons removed as part of the hydrogen atoms to molecular O2 with simultaneous synthesis
of ATP.
◦ first process takes place in the matrix of the mitochondria while the second process is located on the inner membrane of the
mitochondria.
◦ oxidative decarboxylation of pyruvate takes place by a complex set of reactions catalyzed by pyruvic dehydrogenase. The reactions
catalyzed by pyruvic dehydrogenase require the participation of several coenzymes, including NAD+ and Coenzyme A.
◦ During this process, two molecules of NADH are produced from the metabolism of two molecules of pyruvic acid (produced
from one glucose molecule during glycolysis). The acetyl CoA then enters a cyclic pathway, tricarboxylic acid cycle, more commonly
called as Krebs’ cycle.

11. oxidative decarboxylation of pyruvic acid in the cytosol, after it enters
mitochondrial matrix undergoes oxidative decarboxylation by a complex set of
reactions catalysed by pyruvic dehydrogenase. The reactions catalysed by
pyruvic dehydrogenase require the participation of several coenzymes,
including NAD+ and Coenzyme A

12. TCA(tricarboxylic acid cycle) cycle commonly called as Krebs’ cycle after the
scientist Hans Krebs who first elucidated it.
1.Condensation with OAA and H2o
and enzyme citrate synthase.
2.Citrate isomerises to iso citrate
3.Two successive d ecarboxylation of
isocitrate results in 2NADH
production and results in succinyl coA
4.Succinyl coA looses coA and forms
succinate releasing GTP=1ATP
5.Succinate then undergoes stepwise
oxidation to produce oxaloacetate
releasing 1FADH2 and 1NADH.

14. Electron Transport System (ETS) and Oxidative Phosphorylation.
ETS is series of hydrogen and electron carriers
located on inner mitochondrial matrix.
Reduced compounds produced by TCA that
NADH2 and FADH2 enter ETS.
Complex 1 is NADH dehydrogenase complex.
Complex II is succinate dehydrogenase
complex. Complex III is cytochromebC1
complex .complex IV is cytochrome c oxidase
contain a,a3 associated withCu2+ centre. Complex
V is F0-F1. mobile carriers in membrane are b/w
CI and CII –ubiquinone/coenzyme Q. And
b/w CIII and CIV –cytochrome C.

16. THE RESPIRATORY BALANCE SHEET
◦ calculations can be made only on certain assumptions that:
◦ • There is a sequential, orderly pathway functioning, with one substrate forming
the next and with glycolysis, TCA cycle and ETS pathway following one after
another.
◦ • The NADH synthesized in glycolysis is transferred into the mitochondria and
undergoes oxidative phosphorylation.
◦ • None of the intermediates in the pathway are utilized to synthesize any other
compound.
◦ • Only glucose is being respired – no other alternative substrates are entering in
the pathway at any of the intermediary stages.

17. Fermentation/aerobic respiration
◦ fermentation and aerobic respiration:
◦ • Fermentation accounts for only a partial breakdown of glucose whereas in
aerobic respiration it is completely degraded to CO2 and H2O.
◦ • In fermentation there is a net gain of only 2 molecules of ATP for each
molecule of glucose degraded to pyruvic acid whereas many 38 molecules of
ATP are generated under aerobic conditions
◦ . • NADH is oxidised to NAD+ rather slowly in fermentation, however the
reaction is very vigorous in case of aerobic respiration.

18. AMPHIBOLIC PATHWAY
“An amphibolic pathway is a biochemical pathway
that includes both anabolic and catabolic
processes.”
*Respiration is the breakdown of the complex
compounds into simple ones to produce energy
ATP. Hence the process is called catabolic
pathway is termed as a catabolic pathway. When
required, proteins or fatty acids are broken down
acetyl-CoA and further processes of respiration
catabolism.
*When the body requires fatty acids or proteins,
pathway stops and the same acetyl-CoA is utilized
acids are manufactured. This process of synthesis
as anabolism.

19. RESPIRATORY QUOTIENT
. The ratio of the volume of CO2 evolved to the volume of O2 consumed in respiration is called the
respiratory quotient (RQ) or respiratory ratio.
RQ= volume of CO2 evolved /volume of O2 consumed.
* If carbohydrates are used as substrate and
are completely oxidized, the RQ will be 1.
*If fats are used in respiration, the RQ is less than 1.
*If proteins are respiratory substrates the ratio would be about 0.9
* Important to recognize is that in living organisms respiratory substrates are often more than one; pure
proteins or fats are never used as respiratory substrates.