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Respiration in Plants

Respiration is a catabolic & exergonic cellular process.

Respiration is an enzymatic process, which is also known as internal respiration/ tissue respiration/ dark respiration/ cellular respiration/ mitochondrial respiration.

An important feature of respiration is liberation of metabolic energy as ATP.

  • Respiratory substrate:

(Carbohydrates → Fats → Protein → others)

When respiratory substrates are carbohydrates like glycogen, starch, sucrose, hexose or fats, then respiration is known as floating respiration.

When protein is oxidised in respiration, then respiration is known as protoplasmic respiration. Protoplasmic components or cellular proteins may oxidised at the time of starvation & disease.

Exceptionally oxidation of proteins in legume seeds in called floating respiration.

Compensation point: It is that value or point in light intensity and atmospheric CO2 concentration when rate of photosynthesis is just equivalent to the fate of respiration in photosynthetic organs so that there is no net gaseous exchange. The value is 2.5-100 ft candles/ 26.91-1076.4 lux in shade plants and 100-400 ft candles/1076.4-4305.6 lux in case of sun plants. It is called light compensation point. There is, similarly, a CO2 compensation point. Its value is 25-100 ppm (25-100 m1.11) in C3 plants and 0-5 ppm (0-5m1.1-1) in C4 plants. A plant cannot survive for a long at compensation point because the non-photosynthetic parts and dark respiration will deplete organic reserve of the plant.

  • Types of respiratory organism

Organism can be grouped into following four classes on the basis of their respiratory habit.

(1) Obligate aerobes: These organisms can respire only in the presence of oxygen. Thus oxygen is essential for their survival.

(2) Facultative anaerobes: Such organisms usually respire aerobically (i.e., in the presence of oxygen) but under certain condition may also respire anaerobically (e.g., Yeast, parasites of the alimentary canal).

(3) Obligate anaerobes: These organisms normally respire anaerobically which is their major ATP­ yielding process. Such organisms are in fact killed in the presence of substantial amounts of oxygen (e.g., Clostridium botulinum and C. tetanl).

(4) Facultative aerobes: These are primarily anaerobic organisms but under certain condition may also respire aerobically.

  • Types of respiration

(A) Aerobic respiration: The complete oxidation of food with the use of-oxygen and when entire carbon released, as CO2 is called as aerobic respiration.

         C6 H12 O6 + 6O2 + 6H2O  6CO2 + 12H2O   + 686 Kcal energy

(B) Anaerobic respiration: This is an incomplete oxidation.

When food is oxidized into alcohol or organic acids without use of oxygen.

During it most of the energy is lost in form of heat.

It occurs in cytoplasm and only 2A TP are produced.

              C6 H12 O6  2C2 H5 OH + 2CO2 + 21 Kcal (2ATP)

Anaerobic respiration was first reported by Kostytchev.

Anaerobic respiration may takes place in bacteria, some lower parasitic animals (Ascaris, Taenia) plants, RBCs & muscles of human body. When oxygen is not available, then food is incompletely oxidised in to some organic compounds like ethanol, acetic acid, lactic acid.

In muscle cells & some bacteria, the energy is produced by' breaking of glucose into lactic acid inside the cells.

The amount of energy released in anaerobic respiration is much less than aerobic respiration.

Fermentation is performed by some fungi & some bacteria (only by microbes) and is an extracellular process. No A TP is produced.  

        C6 H12O6  2CO2 + 2C2H5OH + Heat. 

Both anaerobic respiration and fermentation are incomplete oxidations.

Inhibitory effect on respiration (anaerobic respiration) of oxygen is called Pasteur effect (Anaerobic→ Aerobic)

  • Steps of respiration

(1) Glycolysis - Occurs in cytosol/cytoplasm

(2) Formation of Acetyl Co-A (link reaction) Peri-mitochondrial space (outer chamber)

(3) TCA cycle or Kreb's cycle: Matrix of mitochondria & cytosol in bacteria.

(4) ETS - Occurs in cristae or inner membrane of mitochondria and oxidative phosphorylation. occurs in oxysome (F1 particle) 

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