Respiration is the process by which plants release energy stored during photosynthesis. There are two types of respiration - aerobic respiration which requires oxygen and occurs in the mitochondria, and anaerobic respiration which does not require oxygen. Respiration involves several stages including glycolysis, the Krebs cycle, and the electron transport chain, which ultimately generate ATP through oxidative phosphorylation. Respiration is essential for plant growth and metabolism as it provides energy for cellular processes and converts stored energy into usable form.

2. Respiration - Definition
The energy stored in photosynthetic
products during Photosynthesis is
released by oxidation of that
products into CO2 & H2O
C6H12O6 + 6O2 + 6H2O
6CO2 + 12H2O + Energy (686 K. Calories)

3. SIGNIFICANCE OF RESPIRATION:
Respiration is an important process because
1. It releases energy which is consumed in various metabolic
processes essential for plant life and activates cell division.
2. It brings about the formation of other necessary compounds
participating as important cell constituents.
3. It converts insoluble food into soluble form.
4. It liberates CO2 and plays a part actively in maintaining the
balance of carbon cycle in nature.
5. It converts stored energy (potential energy) into usable form
(kinetic energy)

4. Respiration is of two types
1. Aerobic respiration – in presence of O2
2. Anaerobic respiration – in absence of O2
Aerobic respiration – The process of producing the cellular
energy involving oxygen

5. Anaerobic respiration
1st step- Glucose 2 Pyruvic acid
In Yeasts: 2 PA 2 Ethyl alcohol + CO2
Glycolysis
Fermentation process
2 molecules of ATP released

6. Stages of Respiration
 Glycolysis
 Link Reaction
 Krebs Cycle
 Electron Transport System Chain
 Oxidative phosphorylation

7. Glycolysis
Greek word- Glykos = ‘sugar’ , lysis = ‘splitting’
Anaerobic process
It is the first step of aerobic respiration
Common step for aerobic and anaerobic respiration
Occur in cytoplasm
Also call EMP pathway (Embden, Meyerhoff, Parnes)

8. 1. Hexo kinase
2. Phospho gluco isomerase
3. Phosphofructokinase
4. Aldolase
5. G 3–P – Dehydrogenase
6. Phosphoglycerokinase
7. Phosphoglyceromutase
8. Enolase
9. Pyruvate Kinase
(6C)
(6C)
(6C)
(6C)
(3C)
(3C)
(3C)
(3C)
(3C)
(3C)
(3C)
Energy
investment phase
/ Preparatory
phase
Payoff phase /
Energy yield

9. Glucose
2 Pyruvic acid
4 ATP
2 ATP
2 NADH
NET GAIN = 2 ATP & 2 NADH
Gross ATP = 8 ATP [1 NADH=3ATP]
Glycolysis

10. Why we get only 2 ATP during anaerobic
breakdown of glucose molecules??
Glucose Ethanol
2 Pyruvate 2 Acetaldehyde
NAD+
NADH
--------------------------------
------------------------------
Alcohol
dehydrogenase
Pyruvate
decarboxylase
G-3P
dehydrogenase

11. OXIDATIVE PENTOSE PHOSPHATE PATHWAY
6-Phosphogluconate

12. The oxidative pentose phosphate pathway plays several roles in plant metabolism:
NADPH is thought to drive reductive steps associated with various biosynthetic reactions
that occur in the cytosol such as lipid biosynthesis and nitrogen assimilation.
Some of the reducing power generated by this pathway may contribute to cellular energy
metabolism
The pathway produces ribose 5 phosphate, a precursor of the ribose and deoxyribose
needed in the synthesis of RNA and DNA respectively.
Another intermediate in this pathway, the four carbon erythrose – 4 - phosphate, combines
with PEP in the initial reaction that produces plant phenolic compounds including the
aromatic amino acids and the precursors of lignin, flavonoids and phytoalexins.
During the early stages of greening, before leaf tissues become fully photoautotrophic, the
oxidative pentose phosphate pathway is thought to be involved in generating Calvin
Cycle intermediates

13. Formation of Acetyl Co A
2 NAD+ 2 NADH
2 Pyruvic acid 2 Acetyl CoA
Coenzyme A
2 CO2
TCA
Cycle
Oxidative Decarboxylation
Link Reaction -
Co-factors:
Magnesium ion
Thiamine pyrophosphate
NAD+
Co-enzyme-A
Lipoic acid

15. Krebs Cycle
• Requires Oxygen (Aerobic)
• Takes place in matrix of mitochondria (Inner membrane)
OAA Citric Acid
Acetyl COA
TCA Cycle

16. TCA
Cycle
Kreb Cycle
ATP
ADP

17. Krebs Cycle Summary
For each Glucose molecule, the Krebs
Cycle produces
6 NADH, 2 FADH2 and 2 ATP
1NADH = 3 ATP
1 FADH2 = 2 ATP
3 NADH, 1 FADH2 and 1 ATP
2 kreb cycle

18. Electron Transport Chain
Oxidative Phosphorylation
Four complex proteins involved
NAD
FAD/FMN
Co-enzyme- Q
Cytochromes- b,c,a,a3
Complex I to Complex IV
Electron transport through electron carriers
Oxidation of Coenzymes & energy is released
Energy utilized for phosphorylation
(ADP + Pi ------- ATP) - Phosphorylation By Oxidation called as
Oxidative Phosphorylation

19. 2H+ 2H+
NADH DH Succinate
DH
Cyt- bc1
complex
Cyt- c oxidase

20. Respiration – Net Energy
Pathway NADH FADH ATP TOTAL
ATP
Glycolysis 2 (6) - 2 8
Oxidative
decarboxylation
2 (6) - - 6
Krebs cycle 6 (18) 2 (4) 2 24
Total ATP 30 4 4 38
TOTAL = 36 ATP

21. Oxidative Phosphorylation Photophosphorylation
It occurs during Respiration It occurs during Photosynthesis
Found inside of Mitochondria Found inside of Chloroplast
Process occurs IM of MC Occurs in Thylakoid membrane
Oxygen is needed Oxygen is not required
ETS made up of Cytochromes ETS made up of PS I & PS II
Electron donor is NADH Electron donor is water
Electron acceptor is O2 Electron acceptor is NADP
Produced ATP molecules are used for
different metabolic reactions
Produced ATP molecules are used for
CO2 fixation in dark reaction

23. Total dry matter = Function of canopy photosynthesis and canopy
respiration
Canopy Photosynthesis - Canopy Respiration = Net Photosynthates (G & D)
Canopy respiration = Dark respiration + Photorespiration
Survival of any plant – decided by metabolic activities
Metabolic activity – ATP required
ATP – obtained from oxidation of food materials (carbohydrates, proteins,
lipids).
Food materials – from photosynthesis
So, photosynthetic/respiratory ratio = >1

24. GROWTH AND MAINTENANCE RESPIRATION
GROWTH
Synthesis and accumulation of
material.
Depends only on actual new growth
made by plant.
Denoted as ‘kP’
k= constant
P= rate of photosynthesis
MAINTENANCE
Repair and restoration, operation of all
metabolic systems.
Turnover, transport, maintenance of
gradients of all sorts – for operating
controls and signal system.
Function of plant size
Denoted as ‘cW’
c= constant
W= dry weight of plant

25. Thus,
Respiration (R) = kP + cW
Hence, rate of photosynthesis > GR + MR

26. RESPIRATORY SUBSTRATES
Respiratory substrate – Any organic plant constituent oxidised partially or
completely in respiratory metabolism
Principal respiratory substrates in cells of higher plants – Carbohydrates
Imp. Respiratory substrates among carbohydrates- Sucrose, Starch
Some other substances as respiratory reserves are:
Castor – Lipid reserve in endosperm
CAM plants – Organic acids
Detached leaves - Proteins

27. RESPIRATORY QUOTIENT (R.Q.)
Substrates RQ
Carbohydrates 1.00
Proteins when ammonia produced in oxidation 0.99
Proteins with amide formation 0.80
Fats 0.70
Organic acids 1.33
(R.Q.) = ---------------------------------
Volume of CO2 evolved
Volume of O2 absorbed

28. ALTERNATE RESPIRATION/ CYANIDE RESISTANT RESPIRATION
CYANIDE – added to actively respiring animal tissues – cyt- c oxidase
inhibited.
Respiration rate – quickly drops to <1% of initial level.
Most plants – cyanide resistant respiration
10-25% in some and in some tissues – 100% uninhibited
Enzyme responsible for O2 uptake – cyanide resistant oxidase (component of
plant mitochondrial ETS called alternate oxidase).

29. SALT RESPIRATION
Roots absorb salt- respiration rate rises.
Rise- energy spent in absorbing salts or ions – the required energy supplied by
increased respiration.
The phenomena – Salt respiration.
Inference – respiration represents increased metabolism – need to generate
energy for active transport of ions.
Relationship- not always linear.
Salt respiration – persists after salts removed.
Hence, no clue to the coupling of respiration and ion transport.

30. WOUND RESPIRATION
Wounding of plant organ – stimulate respiration.
Initiate meristematic activity in region of wound – result in ‘wound callus’.
Wounding increased – sugar content
Increase in respiration – increased availability of respiratory substrate in
wounded tissues.

31. MEASUREMENT OF RESPIRATION
By quantitative determination of CO2 evolved or O2 consumed.
Different methods of measurement of respiration
Weight method
Titration method
Quantitative method
Manometric method
Infrared CO2 analyser or paramagnetic O2 analyser

32. Weight method
* CO2 produced by plant – trapped in barium hydroxide solution.
* Weight of Barium carbonate formed - CO2 produced
Titration method
* CO2 produced – dissolved in NaOH
* Amount of CO2 absorbed – estimated by titration
Quantitative method
* Released CO2 – measured by passing an air stream through sealed chamber
containing plant tissue into alkaline solution
* Changes in ph and E.C recorded.
* Recorded changes - CO2 released by tissue calculated

33. Manometric method
* CO2 release or O2 uptake – measure by manometer.
* Sliced plant samples- suspended in water in a flask.
* Changes in amount of respiratory gases – reflected in change in pressure.
* Changes in pressure- measured by manometer.
Infrared CO2 analyser or paramagnetic O2 analyser
* Instrument measuring changes in CO2 or O2 of atm. and plants in sealed
chambers.
* A membrane bound polarographic electrode sensitive to O2 can measure
changes in the concentration of O2 in a solution