Aerobic respiration occurs in four main stages: glycolysis, acetylation, the Krebs cycle, and the electron transport system. Glycolysis breaks down glucose into pyruvic acid, producing a small amount of ATP. Acetylation converts pyruvic acid into acetyl-CoA. The Krebs cycle further oxidizes acetyl-CoA, producing more ATP and NADH/FADH2. Finally, the electron transport system uses oxygen to further oxidize NADH/FADH2, producing the most ATP through chemiosmosis. Aerobic respiration is highly efficient, producing 38 ATP from one glucose molecule.

1. c3,c4,camplants
Presented By,
Dr.Thirunahari Ugandhar

2. Aerobic respiration
Aerobic respiration is completed in
Glycolysis
Oxidative carboxylation (Acetylation)
Krebs cycle
Electron transport system

3. Glycolysis
 The sequence of reactions in which glucose (6C) is broken
down into two molecules of pyruvic acid(3C).
 Also called as EMP pathway named after their
discoverers Embden, Meyerhoff, and Paranas.
 1st step in breakdown of glucose.
 Does not require presence of oxygen & there is no output of
carbon dioxide.
 Occurs in cytoplasm of cell.
 Involves series of 10 reaction, each controlled by a specific
enzyme.

4. The reactions are studied in three groups:
Activation or phosphorylation of glucose
molecule.
Cleavage or fragmentation
Oxidation.

5. Activation

6. Activation or
Phosphorylation of Glucose1. Phosphorylation of glucose
◦ Glucose is converted to Glucose 6- phosphate
2. Isomerisation
◦ Glucose 6- phosphate isomerised to Fructose 6-phosphate.
3. Second phosphorylation
◦ Fructose 6-phosphate is phosphorylased to Fructose 1, 6-
diphosphate by enzyme Phosphofructokinase(PFK).

7. Cleavage or Fragmentation
4. Cleavage
◦ Fructose 1, 6 bi phosphate is an unstable compound and
splits to produce 3C compounds 3PGAL and DHAP.
5. Isomerisation
◦ Glycolysis utilizes only PGAL, therefore DHAP is
isomerised to 3PGAL

8. Oxidation
6. Oxidative phosphorylation(Dehydrogenation):
o 3PGAL is oxidized by removal of Hydrogen(H2) and
simultaneous phosphorylation of the product resulting in 1,3
Di PGA
7. ATP synthesis:
o 1,3 Di PGA is converted to 3 PGA by release of one
phosphate group.
8. Isomerization:
o Phosphate group at 3rd carbon is shifted to 2nd i.e. 3 PGA to
2PGA.

9. 9. Dehydration :
o 2 PGA loses a molecule of water and gets converted to
PEPA
10. ATP synthesis (formation of Pyruvic acid)
o PEPA is converted to Pyruvic acid by removal of phosphate
group.

10. Net reaction of Glycolysis
+ 2 ADP +2 NAD+ 2 C3H4O3 + 2 ATP +2NADH+C6H12O6
H+
Net gain of ATP
+ • =From6A2TNPADH2 Direc4tlAyTfoPrmed U2tiAlizTePd Net8gaAinTP
Pyruvic
acid

12. Fate of Pyruvic Acid
Glucose
Glycolysis
Pyruvic acid
Anaerobic
respiration
Aerobic
respiration
O2 isused O2 is not used

13. Acetylation
 Conversion of Pyruvic acid into Acetyl Co-A
 Reaction starts in cytoplasm and completes in
mitochondria
Pyruvate(3C)
Co A +
NAD +
CO2
+
NADH2
Acetyl Co- A(2C)
Pyruvic
dehydrogenas
e

14. Kreb’s cycle
 Also called TCA or Citric Acid cycle.
 Stepwise, cyclic complete oxidation and
decarboxylation of Pyruvic acid into CO2 AND H2O with
release of energy.
 Named after Hans Krebs who traced the sequence of
reactions.
 Takes place in matrix of mitochondria.
 Des not consume ATPmolecules.

15. The reactions are as follows:
1. Condensation:
 Acetyl Co-A (2C) combines with Oxaloacetic acid (4C) in
presence of water to form Citric acid(6C).
2. Isomerisation:
 Citric acid first dehydrates to form Cis Aconitic acid and then
rehydrates to form Isocitric acid(6 C).
3. Dehydrogenation:
 Isocitric acid oxidizes to form Oxalosuccinic acid(6C).
4. Decarboxylation:
 With release of a CO2 Oxalosuccnic acid converts to α-Keto
glutaric acid(5C).

16. 5. Oxidative decarboxylation:
 α- Ketoglutaric acid oxidizes & decarboxylates and the product
combines with Co-A to form Succinyl Co-A(4C).
6. ATP synthesis:
 Succinyl Co-A is hydrolysed to Succinic acid(4C).
7. Dehydrogenation:
 Succinic acid is oxidized to Fumaric acid (4C).
8. Hydration:
 Fumaric acid is converted to Malic acid (4C) by addition of
water.
 Malic acid is then oxidised to form Oxaloacetic acid(4C).

18. Net gain of ATP
8 NADH2 - 24 ATP
2FADH2 - 4 ATP
Direct synthesis - 2 ATP
Total gain of ATP - 30ATP
ATP synthesis through
ETS

19. Electron Transport System
 Final step of aerobic respiration.
 Most ATP and metabolic water generated in this step.
 Located in inner mitochondrial member(cristae &
oxysomes).
 Individual members are called electron carriers.
 Electrons from NADH and Succinate pass through the
ETS to oxygen, which is reduced to water.

21. NADH
Complex I
UQ
Cytochrome c
Complex IV
O2
Complex II
Complex III
Succinate

22. 2H+ + 2e- + ½ O2 H2O
NADH2 or FADH2 NAD or FAD + 2H+ + 2e-
Formation of metabolic water

23. Steps
Reduced
coenzymes
ATP through
ETS
Direct
ATP
Total ATP
1.
Glycolysis
2 NADH2 22NADH X 3= 6ATP 2ATP 8ATP
2.
Acetylation
2 NADH2 22NADH X 3 = 6ATP - 6ATP
3. Krebs
cycle
6 NADH2 2NADH X 3 = 18ATP
2ATP 24ATP
2 FADH2 FADH2 X 2 = 4ATP
C6 H12 O6 + 6 O2 6 CO2 + 6 H2 O + 38ATP

24. Significance ofAerobic
Respiration
 1 glucose molecule produces 38 ATPmolecules.
 Glucose molecule consists 686 k.cal energy.
 Of these only 277.4 k.cal energy (38 X 7.3 k.cal) is
conserved in ATP.
 Remaining energy is lost as heat energy.
 Efficiency of this respiration is 40%.

25. Anaerobic respiration
 The
partial
incomplet
e
oxidation
of organic
food in
the
absence
of

26. Mechanism
It is completed in 3 main steps.
1. Glycolysis
2. Decarboxylation
3. Reduction

27. Glycolysis
 First step is similar to glycolysis of aerobic respiration.
C6H12O6 + 2ADP +2NAD+ 2C3H4O3 +2 ATP
+2NADH+H+

28. Decarboxylation
 Pyruvic acid is decarboxylated to form Acetaldehyde
(2C) and CO2 by enzyme pyruvate decarboxylase.
2CH3CO COOH 2CH3CHO + 2
CO
2
Pyruvate
Decarboxylas
e
Pyruvic acid Acetaldehyde

29. Reduction
Acetaldehyde Ethyl
Alcohol
 Acetaldehyde is reduced to Ethyl Alcohol by
NADH2 formed in Glycolysis with the help of
enzyme Alcohol Dehydrogenase.
Alcohol
Dehydrogena
se

30. Significance of Respiration
 Release of energy
 Synthesis of ATP
 Stepwise release of energy
 Growth and development
 Energy for biosynthesis
 Role of intermediates
 Balance of CO2 & O2
 Fermentation

31. Thank you

32. Photosynthesis Live Reaction

33. C 3 Plants
 Called C3 because the first product of photosynthesis is
a 3-carbon molecule.
 Most plants are C3,usually on dicot plant .
 C3 photosynthesis is a multistep process in which the carbon from
CO2 is fixed into stable organic products, it occurs in virtually all
leaf mesophyll cells.
 Rubisco, the enzyme involved in photosynthesis, is also the enzyme
involved in the uptake of CO2.
 Photosynthesis takes place through out the leaf.
 Advantage of C3 :
-More efficient than C4 plants under cool and moist conditions and
under normal light because fewer enzymes and no specialized
anatomy.

35. Comparison # C3:
1. Plants operate Calvin Cycle only in all green cells.
2. There is only one CO2 acceptor, i.e., RuBP.
3. The first stable product of photosynthesis is PGA (a
C3 acid).
4. “Kranz anatomy” is not found. There is no
chloroplast dimorphism. They have well defined grana
with both PS-I and PS-II.
5. There is no CO2 concentrating device. Fixation and
assimilation of C takes place only through Calvin cycle
in the day. So, there is no decarboxylation mechanism.
:6. Photorespiratory toss of photo- synthates is very
prominent due to dual action of rubisco and lack of
PEPcase. Up to 40% of photosynthates may be lost.
.

36. 7. CO2 compensation point is 40-100 µ||-1.
8. Intracellular CO2 concentration in light is 200 µ||-1.
9. Stomatal frequency is 2000 – 31000.
10. Water use efficiency is 1-3 gCO2 fixed/kg water
transpired.
11. Maximum growth rate is 5-20g m-2 d-1.
12. Maximum productivity 10-30 t ha-1y-1.
13. Typical species of economic importance are wheat,
barley, rice, potato.
14. 89% world flora (in species number).
15. Widely distributed and dominant in forests.

38.  Called C4 because the first initial photosythesis
product is a 4-carbon compound.
 C4 photosynthesis occurs in the more advanced
plant taxa and is especially common among
monocots, such as grasses and sedges
 C4 photosynthesis represents a biochemical and
morphological modification of C3 photosynthesis to
reduce Rubisco oxygenase activity and thereby increase
photosynthetic rate in low CO2 environments

39.  Photosynthesis takes place in inner cells
 Surrounding the bundle sheath cells are mesophyll cells
in which a much more active enzyme,
Phosphoenolpyruvate (PEP) Carboxylase
 Uses PEP Carboxylase for the enzyme involved in the
uptake of CO2. This enzyme allows CO2 to be taken into
the plant very quickly, and then it delivers the CO2
directly to Rubisco for photosynthesis
 The additional cost of C4 photosynthesis is the adenosine
triphosphate (ATP) requirement associated with the
regeneration of PEP from pyruvate.
 C4 photosynthesis occurs primarily within
monocotyledonous plants

41.  Advantage of C4:
 Photosynthesis effecient than C3 plants under high
light intensity and high temperatures because the
CO2 concentration is high, not allowing it to grab
oxygen and undergo photorespiration.
 Has better water use efficiency because PEP
Carboxylase brings in CO2 faster and so does not need
to keep stomata open as much (less water lost by
transpiration) for the same amount of CO2 gain for
photosynthesis.

42. Comparison # C4:
1. Plants operate C4 cycle in MC in addition to C3 cycle operating in
BSC.
2. There are two C02 acceptors — PEP and RuBP.
3. The first stable product is malate or aspartate (aC4acid).:
4. The leaves show “Kranz anatomy”. The chloroplasts are dimorphic.
The MC chloroplasts are granal whereas the BSC chloroplasts are
agranal lacking PS-II.
5. Plants are specially characterized by CO2 concentrating mechanism.
So, there is initial carboxylation in MC followed by decarboxylation in
BSC. Both are occurring in same time (day) but separated in space.
6. Photorespiration cannot be detected due to the high activity of PEP
case in MC. The C4 cycle gears the C3 cycle by pumping C02 in BSC.
Rubisco cannot behave as oxygenase.
7. 0-10 µ||-1.

46. 8. 100 µ||-1.
9. 10000-16000.
10. 2 – 5 g of CO2 fixed/kg of water transpired.
11. 40-50g m-2d-1.
12. 60 – 80 t ha -1 y-1.
13. Maize, millet, sugarcane, sorghum.
14. < 1%.
15. Warm to hot open sites (grassland).

47. Comparison # CAM:
1. Plants operate only C3 cycle in MC for carbon
assimilation.
2. Same as C4.
3. The initial fixation product is malate in dark, which
remains stored in vacuole.
4. No “Kranz anatomy” is found. The chloroplasts are
not dimorphic.
5. Plants show CO2 accumulating device as malate
during night as they are adapted to arid zone. So,
acidification and de-acidification occur in the same
space (MC) but separated in time. The former takes
place in dark while the latter takes place in light.
6. Photorespiration cannot be detected as the stomata
remain closed during day. The photo-respiratory
CO2 cannot escape instead is re-fixed by Rubisco.