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Fermentation and Factors Affecting Cell Respiration


Table of Content


Respiratory Quotient (R.Q.)

Factors Effecting Cell Respiration

Difference Between Glycolysis and Kreb's Cycle


  • Fermentation

Cruick Shank & Pasteur (1898).

Fermentation is much similar to anaerobic respiration, but this is an extracellular process & substrate is present outside the cell. Energy is released as heat, no A TP generated.

Buchner discovered the enzyme zymase complex, which is responsible for alcoholic fermentation. Types of Fermentation:

(i) When the one type of product formed in fermentation then it is called homo fermentation.

(ii) When the products of fermentation process are more than one type, then process is called heterofermen tation. 

(1) Alcoholic fermentation:

This is the oldest & the best known type of fermentation performed by yeast & some bacteria. 

Alcoholic Fermentation

(2) Lactic acid fermentation: It occurs during curd formation. 

(3) Acetic acid fermentation: This is aerobic fermentation 

(4) Butyric acid fermentation:

In rancid butter, butyric acid fermentation takes place. Also in jute fiber.     

Other example are curring of tea, tanning of leather, retting of fibers, processing of Tobacco 

  • Resouratory Quotient (R.Q.)

The ratio of the volume of CO2 released to the volume of O2 taken in respiration is called RQ.

Value of RQ depends upon the type of respiratory substrate used & measured by Ganong's respirometer.

1. Carbohydrates: R.O. = 1

C6H12O6 + 6O2 + 6H2O ® 6CO2 + 12H2O + E

2. Fat/Oil: RQ = 0.70 or R.Q. < 1

2C51H98O6 + 145O2 ® 102 CO2 + 98 H2O + E

Fatty seeds germination-castor, RQ. < 1

At the time of formation of fatty seeds, (maturing fatty seed) RQ. is more than 1 because more CO2 is released than 02 consumed.

3. Organic acids: (In succulent xerophytes at day time)

Malic acid:

C4-H6O5 + 3O2 → 4CO2 + 3H2O + Energy

Oxalic acid R.Q. = 4

Citric acid RQ. = 1.3

4. Incomplete oxidation of carbohydrates:

In CAM plants during night: RQ. = 0

2C6H12O6  + 3O2 → 3C4H6O5 + 3H2O + Energy

5. Protein: R.Q. = 0.8 or 0.9 or < 1

6. Anaerobic respiration: RQ = ¥

  • Factors Effecting Cell Respiration

1. Temperature:

Optimum temp for respiration is between 20-35°C

Maximum temp. is around 45°C

At low temp respiration is low due to inactivation of enzymes {Freeze preserve the food) while at very high temp. decreases. as enzyme get denatured.

Q10 = 2 to 3 for respiration.

Production of potato crop is high on the hill areas due to low temp throughout year.

CRPI (Central. potato Research Institute is situated at Kufri-Shimla (H.P.)

2. Oxygen:

The inhibition of anaerobic respiration by O2 concentration is called as Pasteur's effect.

The minimum amount of oxygen, at which aerobic respiration takes place & anaerobic respiration become extinct is called as extinction point.

Oxygen concentration at which both aerobic & anaerobic respiration take place Simultaneously is called as transition point.

3. CO2: If CO2 concentration increases, then rate of respiration decreases in plants, (because stomata get closed).

4. Salts: If a plant is transferred from water to salt solution, it's respiration increases, this is known as salt respiration. Because absorption of ions requires metabolic energy.

5. Hormones:

IAA, GA & cytokinin Increase the respiration rate. The rapid increase in rate of respiration during ripening of fruits and senescence of leaves and plant organs is called as "Climacteric respiration". This rate is decrease after sometime.

It is due to production of ethylene hormone:

6. Light: Rate of respiration increases with increase in light intensity.

Light controls the stomatal opening & influence on temp and also produce respiratory substrates.

7. Injury, disease & wounds: The respiration increases due to injury wounding & infection.

8. Inhibitors: CN, azides. DNP (Dinitrophenol), CO, rotenone, antimycin, amytal, etc inhibit the respiration.

9. Age: Rate of respiration is more in young cells.

Rate of respiration at meristem apex is high.

10. Water: Seeds are slow respiring part of plants, because dry seeds are deficient of H2O.  


Difference Between Glycolysis and Kreb's Cycle


Kreb's cycle

It takes place in the cytoplasm.

It occurs in aerobic as well as anaerobic respiration.

It consists of 9 steps.

It is a linear pathway.

It oxidizes glucose partly, producing pyruvate.

It consumes 2 A TP molecules.

It generates 2 ATP molecules net from 1 glucose molecules.

It yields 2 NADH per glucose molecule.



It does not produce CO2,

All enzyme catalysing glycolytic reactions are dissolved in cytosol.

It takes place in the matrix of mitochondria.

It occurs in aerobic respiration only.

It consists of 8 steps.

It is a cyclic pathway.

It oxidises acetyl coenzyme A fully.

It does not consume ATP

It generates 2 GTP / ATP molecules from 2 succinyl coenzyme A molecules.

It yields 6 NADH molecules and 2 FADH2 molecules from 2 acetyl coenzyme A molecules.

It produces CO2.

Two enzymes of Krebs cycle reactions are located in the inner mitochondrial membrane, all others are dissolved in matrix]

Structure of ATP

Nicotinamide adenine dinucleotide phosphate/ Nicotinamide adenine dinucleotide (NADP/ NAD): It is called universal hydrogen acceptor, produced during aerobic respiration (glycolysis + Krebs cycle) and also in anaerobic respiration, work as coenzyme in ATP generation Via electron transport system. NADP have one additional phosphate.

NAD plays a crucial role in dehydrogenation processes. Some dehydrogenases do not work with NAD, but react with NADP (Nicotinamide adenine dinucleotide phosphate). Formerly called Coenzyme II or Triphosphopyddine nucleotide = TPN Nicotinamide is a vitamin of B group.

First NAD and NADP both functions as hydrogen acceptors. Later H ions and electrons (e-) from these are transported through a chain of carriers and after being released at the end of a chain react with O2 and from H2O (see Electron Transport chain). During the release of 2 electron from 2H+ atoms from NAD. 2H and their reaction with O2 to form water, 3 ATP molecules are synthesized. 

Anaerobic respiration pathway

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