RESPIRATION IN PLANTS

POINTS TO REMEMBER :

• The breaking of C-C bonds of complex compounds through oxidation within the cells, leading to release of considerable amount of energy is called respiration.
• The compound that oxidized during this process is known as respiratory substrates.
• In the process of respiration the energy is released in a series of slow step-wise reactions controlled by enzymes and is trapped in the form of ATP.
• ATP acts as the energy currency of the cell.

Glycolysis : 

• The term has originated from the Greek word, glycos =glucose, lysis = splitting or breakdown means breakdown of glucose molecule.
• It is also called Embeden-Meyerhof-Paranus pathway. (EMP pathway)
• It is common in both aerobic and anaerobic respiration.
• It takes place outside the mitochondria, in the cytoplasm.
• One molecule of glucose (Hexose sugar) ultimately produces two molecules of pyruvic acid through glycolysis.
• Glucose and fructose are phosphorylated to give rise to glucose-6-phosphate, catalyzed by hexokinase.
• This phosphorylated form of glucose is then isomerizes to produce fructose-6-phosphate.
• ATP utilized at two steps:
  • First in the conversion of glucose into glucose-6-phosphate
  • Second in fructose-6-phosphate→fructose 1, 6-diphosphate.
  
  
• The fructose-1, 6-diphosphate is split into dihydroxyacetone phosphate and 3-phosphoglyceraldehyde (DPGA).
• In one step where NADH + H⁺ is formed form NAD⁺; this is when 3-phosphogleceraldehyde (PGAL) is converted into 1, 3-bisphophoglyceric acid (DPGA).
• The conversion of 1, 3-bisphophoglyceric acid into 3-phosphoglyceric acid is also an energy yielding process; this energy is trapped by the formation of ATP.
• Another ATP synthesized when phosphoenolpyruvate is converted into pyruvic acid.
• During this process 4 molecules of ATP are produced while 2 molecules of ATP are utilized. Thus net gain of ATP is of 2 molecules.

FERMENTATION :

• There are three major ways in which different cells handle pyruvic acid produced by glycolysis:
  • Lactic acid fermentation.
  • Alcoholic fermentation.
  • Aerobic respiration.
  
  
• Alcoholic fermentation :
  • The incomplete oxidation of glucose to achieved under anaerobic conditions by sets of reactions where pyruvic acid is converted into CO₂ and ethanol.
  • The enzyme pyruvic acid decarboxylase and alcohol dehydrogenase catalyze these reactions.
  • NADH + H⁺ is reoxidised into NAD⁺.
  
  
• Lactic acid fermentation:
  • Pyruvic acid converted into lactic acid.
  • It takes place in the muscle in anaerobic conditions.
  • The reaction catalysed by lactate dehydrogenase.
  • NADH + H⁺ is reoxidised into NAD⁺.
  
  
• Aerobic respiration:
  • Pyruvic acid enters into the mitochondria.
  • Complete oxidation of pyruvate by the stepwise removal of all the hydrogen atoms, leaving three molecules of CO₂.
  • The passing on the electrons removed as part of the hydrogen atoms to molecular oxygen (O₂) with simultaneous synthesis of ATP.

AEROBIC RESPIRATION:

• The overall mechanism of aerobic respiration can be studied under the following steps :
• Glycolysis (EMP pathway)
• Oxidative Decarboxylation
• Krebs’s cycle (TCA-cycle)
• Oxidative phosphorylation

CBSE Biology (Chapter Wise) Class XI ( By Mr. Hare Krushna Giri ) 
Email Id : [email protected]