This document discusses cellular respiration in plants. It covers: 1) Respiration is the process by which energy stored in carbohydrates is released through the controlled breakdown of glucose and coupled to ATP synthesis. 2) There are three main stages of respiration - glycolysis, the TCA cycle, and the electron transport chain. Glycolysis occurs in the cytoplasm and partially breaks down glucose, the TCA cycle fully breaks down pyruvate in the mitochondria, and the electron transport chain generates ATP using an proton gradient across mitochondrial membranes. 3) The efficiency of aerobic respiration is around 40% while anaerobic respiration is only around 2% efficient due to the lower ATP yield. A variety of factors like

1. Respiration
• Biological process whereby the energy
stored in carbohydrates from PS is released
in a step-wise, controlled manner.
• Energy released is coupled to the synthesis
of ATP.
• ATP is essential for plant cell maintenance,
growth and development

2. Carbohydrate Conversion
• Starch glucose
• Sucrose + water glucose + fructose

3. Equation for Aerobic Respiration
C6H12O6 + 6O2 + 6H2O 6CO2 + 12H2O + energy
(glucose) (ATP)
1 mole glucose 36 ATP

4. Efficiency of Aerobic Respiration
• ADP-P bond releases -7.6 kcal/mol ATP
when bond is broken
• Theoretical energy yield from burning 1mol
glucose in a calorimeter = -686 kcal/mol
• Practical yield from burning 1mol of glucose
in the cell with oxygen = 36ATP
 36 ATP X -7.6 kcal/mol = -274 kcal/mol glucose
 274/686 kcal/mol X 100 = 40% efficiency

5. Efficiency of Anaerobic Respiration
• ADP-P bond releases -7.6 kcal/mol ATP
when bond is broken
• Theoretical energy yield from burning 1mol
glucose in a calorimeter = -686 kcal/mol
• Practical yield from burning 1mol of glucose
in the cell without oxygen = 2 ATP
 2 ATP X -7.6 kcal/mol = -15.2 kcal/mol glucose
 15.2/686 kcal/mol X 100 = 2.2% efficiency

6. 3 Stages of Respiration
• Glycolysis
• TCA Cycle
• Electron Transport Chain

7. Glycolysis
• Occurs in all living organisms
• Only stage which can occur without oxygen
• Oldest stage of respiration
 operated for billions of years in anaerobic organisms
• Converts glucose to 2 pyruvates in cytosol
 with O2 goes on to TCA cycle
 without O2 pyruvate is converted to lactate or ethanol
(fermentation)
• Yields 2ATP/mole glucose in the absence of O2

8. Glycolysis
Glucose (6C)
2 Pyruvate (3C)
Ethanol Lactate
TCA Cycle
CO2
+O2
-O2 -O2

9. TCA
cycle

11. Electron Transport System
NADH and FADH2
e-
e-
4e-
+ 4H+
+ O2 2H2O
cyt. oxidase
H+
H+
ATP

12. Chemiosmotic model
H+
H+
H+
H+
H+
H+ H+
H+
H+
H+
H+
H+
H+
H+
H+
Ion concentration difference represents a source of
free energy

13. Chemiosmotic model
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
The energy represented by the H+
gradient is converted to a
chemical form (ATP) via the ATP synthase

15. 3 Stages of Respiration
• Glycolysis
 cytoplasm
 with or without oxygen present
 breaks glucose (6C) into 2 pyruvates (3C)
• TCA Cycle
 mitochondrial matrix
 only if oxygen present
 converts pyruvate via acetyl CoA into CO2; generates
NADH and FADH2
• Electron Transport Chain
 mitochondrial membranes = cristae
 transfers electrons from NADH and FADH2 to reduce
O to H O and generate ATP

16. Mitochondria
• Spherical to oval
 about 1 micron diameter
 # mito./cell increases with demand for
respiration; 300-1000/root tip cell
• Double-membrane bound
 outer smooth
 inner folds forming cristae
controls movement in/out
site of electron transportm
• Matrix
 soluble phase
 site of TCA cycle; DNA, RNA, ribosomes
matrix
cristae

17. Alternate Fates of Glucose C
• Not all C respired to CO2
• Intermediates of respiration branch off:
 amino acids
 pentoses for cell wall structure
 nucleotides
 porphyrin biosynthesis
 fatty acid synthesis
 lignin precursors
 precursors for carotenoid synthesis, hormones

18. Factors Affecting Resp. Rate
• [Substrate]
• [ATP]
• [Oxygen]
• Temperature
• Plant type
• Plant organ
• Plant age

19. Factors: Substrate Availability
• Resp. higher right after sundown compared
to right before sunrise due to [S]
• Shaded leaves respire slower than lighted
leaves
• Starvation of plant tissue results in
utilization of proteins
• High [ATP] in cell and get negative
feedback on resp.

20. Factors: [Oxygen]
• No effect until [O2] < 1%
 Cyt oxidase not sensitive to O2 until 0.05%
• O2 diffuses in water 10,000 X slower than in air
• Some plants have intercellular air system, e.g.,
aerenchyma in shoots and roots (rice)
• Very low levels of O2 see accelerated
breakdown of sugars to ethanol and CO2
evolved = Pasteur Effect

21. Factors: Temperature
• Q10 for respiration is 2.0 - 2.5 between 5 and
25C
• Q10 = rate of process at one temperature
divided by the rate at 10C lower temp.
 Decreases with most plant tissues at 30-35C
O2 being used so fast, it can’t diffuse fast enough
into tissues
• Tropical regions - 70-80% PS C lost to resp.
due to high night temperatures and resp.
rates

22. Factors: Plant Type/Organ/Age
• Resp. rate tends to increase with age of plant
 Young trees lose about 1/3 daily PS C to resp. and
doubles with older trees as ratio of PS/Non-PS
tissue decreases
• Greater metabolic activity = greater resp. rates
 Root tips, dev. buds and meristematic regions in
general have higher respiration rates
 In veg. tissues, resp. decreases from the tip to the
mature regions
• Seeds - low resp. rates, dormant, desiccation
results in slowdown of respiration

23. Factors: Plant Type/Organ/Age (cont.)
• Ripening Fruit
 Resp. high when young cells are dividing and growing
• Climacteric Fruit (apples, tomatoes)
 Sharp increase in rate immediately before fruit ripening
= climacteric rise in respiration
 Coincides with full ripeness and flavor and preceded by
huge increase in ethylene production
 This leads to senescence and decrease in respiration
• Non-climacteric Fruit
 Citrus, cherries, grapes, pineapple, strawberries
 Insensitive to ethylene

24. Controlled Atmosphere Storage
• Lower O2 (2% - 3%) & raise CO2(5% - 10%)
 slows down resp.
• No ethylene
 high CO2 also inhibits ethylene synthesis
• Temps. typically about -1 to -0.5C
• Pick apples in Sept./Oct. when green and
immature and store in CA
 expose to normal air with ethylene when ready to
sell fresh apples in March

25. Cyanide Resistant Respiration
• Aerobic resp. (cyt oxidase) in plants and
animals inhibited by CN-
and N3
-
(azide)
 bind to Fe in enzyme and halts e-
transport
• Animals: CN causes resp. to decrease fast,
virtually irreversible and fatal
• Plants: display a 10-25% CN-resistant resp.
and alternate pathway for electron flow
 electron flow branches off to alternate oxidase
 less ATP produced

26. Cyanide Resistant Respiration (cont.)
• Metabolic Role?
 No clear role
 Operates when cyt oxidase poisoned
 Energy overflow hypothesis
overflow for electrons when resp. rate exceeds
demand for ATP; high with high carbo. levels
 Skunk cabbage, Voodoo lily, Stinking lily: CN-
res. pathway causes temp. of spadix to increase
10-20C.
volatilization of odiferous cmpds which attract
pollinators

27. Any Question?