Tiêu đề RESPIRATION IN PLANTS.pdf ✅

 Digital www.allendigital.in [ 141 ] 1. Introduction : • The breaking of C – C single bond of complex compounds through oxidation within the cells, leading to release of considerable amount of energy and the trapping of this energy for synthesis of ATP is called cellular respiration. • During cellular respiration or oxidation within a cell, all the energy contained in compounds is not released in a single step because in single if the complete energy is released it may be converted into heat. So the energy during cellular respiration is released in a series of slow step wise reactions controlled by enzymes and it is trapped as chemical energy in the form of ATP. • ATP thus synthesised, is broken down whenever and wherever energy needs to be utilised, hence ATP act as the energy currency of the cell. • The compounds that are oxidised during the process of cellular respiration are called respiratory substrates, these are usually carbohydrates but except these fats, proteins & organic acids can also be used as respiratory substrates. • Primarily carbohydrates (mainly glucose) are used as respiratory substrate. In the absence or less availability of carbohydrates, the respiratory substrates can be fats & proteins. Respiratory substrate Gross Calorific value Physiological value Carbohydrate 4.1 kcal/g 4.0 kcal/g Protein 5.65 kcal/g 4.0 kcal/g Fat 9.45 kcal/g 9.0 kcal/g • The sequence of use of respiratory substrates – (i) Carbohydrate (ii) Fat (iii) Protein • Organic acids such as malic acid etc. can be used as respiratory substrates in some plants, under certain conditions. Features of Cellular respiration: (i) Cellular respiration is an amphibolic process. Reason: The carbon skeleton (Intermediates of respiration) produced during respiration is used as precursors for biosynthesis of other molecules in the cell. (ii) Cellular respiration is an exergonic process. Reason: The breaking of C–C bonds of complex compounds through oxidation within the cells, leading to release of considerable amount of energy. Photosynthesis Sugar synthesis (C6H12O6) Breaking C–C bonds or oxidation Cellular respiration ATP Synthesis Respiration in plants 04
NEET : Biology [ 142 ] www.allendigital.in  Digital 2. Do Plants Breathe? • Plants, unlike animals, have no specialised organs for gaseous exchange but they have stomata and lenticels for this purpose. • There are several reasons why plants can get along without respiratory organs. • First, each plant part takes care of its own gas-exchange needs. There is very little transport of gases from one plant part to another. • Second, plants do not present great demands for gas exchange. Roots, stems and leaves respire at rates far lower than animals do. Only during photosynthesis are large volumes of gases exchanged and, each leaf is well adapted to take care of its own needs during these periods. When cells photosynthesis, availability of O2 is not a problem in these cells since O2 is released within the cell. • Third, the distance that gases must diffuse even in large, bulky plants is not great. Each living cell in a plant is located quite close to the surface of the plant. In stems, the ‘living’ cells are organised in thin layers inside and beneath the bark. They also have openings called lenticels. The cells in the interior are dead and provide only mechanical support. Thus, most cells of a plant have at least a part of their surface in contact with air. This is also facilitated by the loose packing of parenchyma cells in leaves, stems and roots, which provide an interconnected network of air spaces. Cuticle Xylem Upper Epidermis Mesophyll cells Lower Epidermis cells Guard cells CO2 O2 Epidermis Complimentary cell Cork cambium Secondary cortex
Respiration in Plants  Digital www.allendigital.in [ 143 ] 3. Types of Respiration : (A) On The Basis Of Type Of Respiratory Substrates: (1) Floating respiration: - When carbohydrate or fats are oxidised inside the cell. Carbohydrates and fats are floating inclusions of cell thus, this is called floating respirations. (2) Protoplasmic respiration: - When protein is oxidised inside the cell. This occurs in starved cell. Protein is constituent of protoplasm thus, this is called protoplasmic respiration. (B) On The Basis of Presence or Absence of O2 : (1) Aerobic (2) Anaerobic/Fermentation Aerobic Anaerobic/Fermentation 1. This accounts for complete oxidation (end products are inorganic) of food (glucose) to CO2 and H2O 1. This accounts for only a partial breakdown of glucose to either lactic acid or ethanol and CO2 2. Its an intermolecular respiration 2. It's an intramolecular respiration. 3. 36 or 38 molecules of ATP gain for each molecule of glucose. 3. There is gain of only two molecules of ATP for each molecule of glucose. 4. NADH is oxidised to NAD+ vigorously. 4. NADH is oxidised to NAD+ rather slowly. 5. O2 remove hydrogen from the system and acts as the final hydrogen acceptor. 5. O2 is absent. Hydrogen acceptor in the system is either acetaldehyde (during alcoholic fermentation) or pyruvate (during lactic acid fermentation) 6. Reaction C6H12O6+602+6H2O→6CO2+12H2O+686 Kcal 6. Reaction C6H12O6→2CH3CH2OH+2CO2+ less than 7% of energy of glucose 'or' C6H12O6→2C3H6O3+ less than 7% of energy of glucose 4. Mechanism of Cellular Respiration : (A) Glycolysis/Emp (Embden, Meyerhof, Parnas) Pathway : i. The term glycolysis has originated from the Greek words glycos for sugar, lysis means splitting. The scheme of glycolysis was given by Gustav Embden, Otto Meyerhof & J. Parnas so glycolysis is often called EMP pathway.
NEET : Biology [ 144 ] www.allendigital.in  Digital ii. In all living organisms whether it is aerobic or anaerobic, the first step in cellular respiration is partial breakdown or oxidation of glucose into two molecules of pyruvic acid and it is called glycolysis. iii. The glycolysis is common phase between aerobic & anaerobic respiration. In anaerobic organisms, it is the only process in respiration. iv. In plants the glucose is derived from sucrose (product of photosynthesis) or from starch (storage carbohydrate). v. Sucrose is converted into glucose and fructose by the enzyme invertase and these two monosaccharides enter the glycolytic pathway. vi Glycolysis occurs in the cytoplasm of the cell, this process is independent of oxygen, it means it can occur in both conditions, presence of O2 or absence of O2. vii. It involves a series of ten biochemical enzymatic reactions in cytoplasm. viii. Glucose and fructose are phosphorylated to give rise to glucose-6-phosphate and fructose-6- phosphate respectively by the activity of the enzyme hexokinase. This phosphorylated form of glucose then isomerises to produce fructose-6-phosphate. Subsequent steps of metabolism of glucose and fructose are same. ix. In glycolysis, a chain of ten reactions, under the control of different enzymes, takes place to produce pyruvate from glucose. • In Glycolysis, no consumption of oxygen & no liberation of CO2 takes place. • In glycolysis, 1 glucose (6C), break down into 2mol. of pyruvic acid (3C) (Partial oxidation). • Pyruvic acid is the key product of glycolysis. • 2 NADH2, produced during the process enter into ETS (In mitochondria) to produce 4ATP (if glycerol phosphate shuttle is present) or 6ATP (if malate aspartate shuttle is present), this ATP formation is called oxidative phosphorylation. • Substrate level phosphorylation [When the substrate releases energy for phosphorylation of ADP (formation of ATP) without ETS then this method of ATP formation is called as substrate level phosphorylation], forms 4 ATP, 2ATP consumed, so 2ATP gained by SLP. (Direct gain) Control of Glycolysis : • In glycolysis first, third and last step are irreversible, these are control points of glycolysis, where process can be controlled, if required. • Step third is the most important control point of glycolysis, this step is regulated by an allosteric enzyme phosphofructokinase. This enzyme is allosterically activated by AMP and allosterically inhibited by ATP. This enzyme is called pacemaker enzyme of glycolysis.