Page 1 : Chapter 14 Respiration in Plants, , , , Introduction:, , v, v, , Q., A., v, v, , v, , All the energy required for life processes is obtained by oxidation of food., , Only green plants and cyanobacteria can prepare their own food by the process of photosynthesis., They trap light energy and convert it into chemical energy that is stored in bonds of carbohydrates, like glucose, sucrose and starch., , Animals are heterotrophic, i.e. they obtain food from plants directly (herbivores) or indirectly, (carnivores)., , Cellular respiration is breakdown of food material within cell to release energy and trapping this, energy for synthesis of ATP., , The breakdown of complex molecules to yield energy takes place in cytoplasm and in, mitochondria., , The breaking of C- C bonds of complex compounds through oxidation within cells, leading to, release of energy is called respiration., , The compounds that are oxidised during this process are known as respiration substrates., During oxidation within a cell, energy contained in respiratory substrates 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 is broken down whenever energy needs to be utilised (Recall ATP cycle). Hence, ATP acts as, the energy currency of cell., , , , , , , , Respiration Combustion, Y Biochemical process. Y Chemical process., Y Under biological control. Y Uncontrolled process., v Energy is released in steps. v Energy is released in a single step., ¥ Temperature is notallowed to rise. v Temperature becomes very high., Y Most of the energy is trapped in ATP. vY ATP is not formed., Y Oxidation occurs at the end of reaction Y Substrates is directly oxidised in, (terminal oxidation). combustion., v¥ Anumber of intermediates are formed. Y No intermediates are formed., , , , , , , , How can plants get along without respiratory organs?, , Each plant part takes care of its own gas exchange needs., , Plants do not have great demands for gas exchange; the rate of respiration is far lower than that of, animals., , 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 plants. The cells in interior are dead and provide only, mechanical support., , Glycolysis (glycos- sugar; lysis- splitting):, , v, , The partial oxidation of glucose to pyruvic acid without help of oxygen is called glycolysis., , 1|Page

Page 2 : Y The scheme of glycolysis was given by Embden, Meyerhoff and Parnas; therefore it is referred to, as EMP pathway., , v Inanaerobic organisms, it is the only process in respiration., , Y Glycolysis occurs in cytoplasm of cell., , v Inplants, glucose is derived from sucrose. Sucrose is converted into glucose and fructose by the, enzyme invertase., , Y Glycolysis occurs in 10 steps, the first five steps constitute preparatory phase. In preparatory, phase, ATP is utilized at two steps: first in the conversion of glucose to glucose 6-phosphate and, second in the conversion of fructose 6-phosphate to fructose 1, 6- bisphosphate., , Y The last five steps constitute pay off phase. In this phase, glyceraldehyde 3- phosphate oxidized to, 1, 3 bisphosphoglyceric acid along with reduction of one molecule of NAD* to NADH. ATP is, formed at two steps: first in conversion of 1, 3 bisphosphoglyceric acid to 3- phosphoglyceric acid, and second in conversion of 2- phosphoenolpyruvate to pyruvic acid., , v Pyruvic acid is the key product of glycolysis., , Note: Three types of chemical transformation occur in glycolysis:, ¢ Phosphorylation: Transfer of phosphate group from ATP and intermediate molecule., e Degradation of carbon skeleton: Conversion of 6-C glucose to 3- € pyruvic acid., e Transfer of hydride ion (H*) with its electron to NAD* forming NADH., , 2|Page

Page 4 : Fate of Pyruvate (Pyruvic acid):, , Absence of, oxygen, , (in yeast), , , , , Ethanol + Carbon dioxide + Energy, (2-carbon molecule), , , , , , , In, cytoplasm Lack of oxygen, Glucose —————> _ Pyruvate Lactic acid + Energy, (6-carbon (3-carbon hes "coilad (3-carbon molecule), molecule) molecule), ae gy Presence of, 5 oxygen, a8 Carbon dioxide + Water + Energy, nm, mitochondria), Fermentation, Alcohol Lactic Acid, Fermentation Fermentation, Alcohol Fermentation: It occurs in Yeast., Pyruvic acid Pyruvic acid decarboxylase Ethyl alcohol + CO2 + 2ATP, Alcohol dehydrogenase, , Lactic acid Fermentation: It occurs in some bacteria., , Pyruvic acid Lactate dehydrogenase, Lactic Acid + 2ATP, , Note:, , v Lactic acid fermentation also occurs in animal muscle cells during exercise, when oxygen is, inadequate for cellular respiration., , v In fermentation, less than 7% of the energy in glucose is released., , v Fermentation process is hazardous to the organism above a critical point. For example: Yeasts, poison themselves to death when the concentration of alcohol reaches about 13%., , Let's Discuss:, , 1. What then would be the maximum concentration of alcohol in beverages that are naturally, fermented?, , 2. How do you think alcoholic beverages of alcohol content greater than 13% are obtained?, , , , , , Glycolysis in under Tight Regulation:, , v_ ATP inhibits phosphofructokinase (PFK) by binding to an allosteric site and lowering affinity of, enzyme for Fructose- 6- phosphate., , v ADP acts allosterically to relieve this inhibition by ATP., , , , 4|Page

Page 5 : Aerobic Respiration:, Y It occurs within mitochondria., v Pyruvate is transported from cytoplasm into mitochondria., v Events that occur in aerobic respiration are:, e The complete oxidation of pyruvate by stepwise removal of hydrogen atoms, leaving three, molecules of COz. This process occurs in matrix of mitochondria., e The passing on of the electrons removed as part of hydrogen atoms to molecular 02 with, simultaneous synthesis of ATP. This process is located on the inner membrane of, mitochondria., , In Mitochondrial Matrix:, , Pyruvic Acid + CoA + NAD* Pytuvate dehydrogenase — Acetyle CoA + CO2 + NADH + Ht, Mg2+, Note:, Y During this process, two molecules of NADH are produced from metabolism of two molecules of, pyruvic acid (produced from one glucose molecule during glycolysis)., Y Acetyl CoA enters Tricarboxylic Acid Cycle, also known as Krebs's cycle., , Tricarboxylic Acid Cycle or Citric Acid Cycle or Kreb’s Cycle:, v TCA cycle starts with condensation of 7, acetyl CoA (2C) with oxaloacetic acid, (OAA- 4C) to yield citric acid (6C)., , Acetyl coenzyme A, , Y CoA released in the reaction is recycled to (2c), participate in oxidative decarboxylation of, another molecule of pyruvate. Calne acid Citric acid, , ¥Y During conversion of succinyl CoA to NADH+HE (6c) co,, succinic acid, a molecule of GTP is NAD* =, synthesised. This is a substrate level NADHHY, phosphorylation. In a coupled reaction, ast nae ns acid, GTP is converted to GDP with 4c) :, simultaneous synthesis of ATP from ADP. co,, Note: Synthesis of ATP during glycolysis NAD*, and Kreb’s cycle is substrate level rae NADER, phosphorylation whereas synthesis of FAD" ccc aa ADP, ATP during electron transport in ETS is (4c) ATP, , called oxidative phosphorylation., , , , , , Conversion of succinic acid to fumaric acid is catalysed by the enzyme succinate dehydrogenase., Note: In eukaryotes, succinate dehydrogenase is tightly bound to inner mitochondrial membrane and, in prokaryotes; it is bound to plasma membrane. It is the only enzyme of Krebs's cycle that is, membrane bound., , , , 5|Page