Respiration in Plants PDF

Respiration in Plants © 2022, Aakash BYJU'S. All rights reserved. Key Takeaway Respiration 1 2 Anaerobic respiration 3 4 Oxidative decarboxylation © 2022, Aakash BYJU'S. All rights reserved. Glycolysis 5 Aerobic respiration 6 Electron transport system 7 8 Respiratory quotient 9 Summary © 2022, Aakas...

Respiration in Plants © 2022, Aakash BYJU'S. All rights reserved. Key Takeaway Respiration 1 2 Anaerobic respiration 3 4 Oxidative decarboxylation © 2022, Aakash BYJU'S. All rights reserved. Glycolysis 5 Aerobic respiration 6 Electron transport system 7 8 Respiratory quotient 9 Summary © 2022, Aakash BYJU'S. All rights reserved. Krebs cycle Respiratory balance sheet Respiration The breaking of the C-C bonds of the substrates (complex compounds) through oxidation within the cells, leading to a release of a considerable amount of energy, is known as respiration. The process of respiration occurs inside a living cell. Hence, this process is also known as cellular respiration. Location of respiration: Cytoplasm and mitochondria Cellular respiration involves: o Breakdown of substrates o Release of energy in the form of ATP Cellular respiration occurs inside living cell. © 2022, Aakash BYJU'S. All rights reserved. Respiratory Substrates Definition: Those organic substances which are oxidised during respiration to release energy inside the living cells are termed respiratory substrates. Example: Carbohydrate (primary), fats & proteins ATP acts as the energy currency of the cell. The energy trapped in ATP is utilised in various energyrequiring processes of the organisms. © 2022, Aakash BYJU'S. All rights reserved. Types of Respiration Based on the availability of oxygen Characteristics Breakdown of glucose Occurs in © 2022, Aakash BYJU'S. All rights reserved. Aerobic respiration Anaerobic respiration Occurs in the presence of oxygen Occurs in the absence of oxygen Cytoplasm, mitochondria and aerobic microbes Cytoplasm and anaerobic bacteria Types of Respiration Respiration Anaerobic respiration Lactic acid fermentation © 2022, Aakash BYJU'S. All rights reserved. Alcoholic fermentation Aerobic respiration Breathing in Plants Apertures responsible for gaseous exchange in plants Stomata Present on the surface of leaves Their opening and closing facilitates gaseous exchange © 2022, Aakash BYJU'S. All rights reserved. Lenticels Present in thick woody stem and root Have loosely packed parenchyma cells that facilitate gaseous exchange Glycolysis Glucose 2x Pyruvic acid + Energy It is a metabolic pathway consisting of several steps. Each step is catalysed by an enzyme. Gustav Embden Otto Meyerhof EMP pathway © 2022, Aakash BYJU'S. All rights reserved. J. Parnas First phase of cellular respiration Glyco = Sugar, Lysis = Splitting Also called EMP pathway Common to most living cells Does not require oxygen Glucose is partially oxidized Takes place in the cytoplasm Glycolysis: Preparatory stage Step 1 Step 2 Step 3 Step 4 Step 5 Dihydroxyacetone phosphate (C3) Glucose (C6) Glucose6-phosphate (C6) ATP ADP Fructose6-phosphate (C6) Fructose- 1,6bisphosphate (C6) ATP ADP Preparatory stage © 2022, Aakash BYJU'S. All rights reserved. Glyceraldehyde3-phosphate (C3) Glycolysis: Payoff stage Step 5 Step 6 2Pi 2 x Pyruvate (Pyruvic acid) (C3) 2 x Phosphoenolpyruvate (C3) 2H2O 2ADP 2ATP Step 9 Step 8 Payoff stage © 2022, Aakash BYJU'S. All rights reserved. 2 x 3-phosphoglyceric acid (C3) Step 7 2 x Triose phosphate 2 x 1,3-bisphosphoglyceric (Glyceraldehyde- 3acid phosphate) (C3) 2NAD+ 2 (NADH+H+) (C3) 2ADP 2ATP 2 x 2 phosphoglycerate (C3) Glycolysis: Enzymes Involved Molecule name Enzymes Glucose Glucose-6-phosphate Fructose-6-phosphate Fructose 1,6-bisphosphate DHAP G3P 1,3-bisphosphoglycerate 3-phosphoglycerate 2-phosphoglycerate Phosphoenolpyruvate Pyruvate © 2022, Aakash BYJU'S. All rights reserved. Hexokinase Phosphoglucose isomerase Phosphofructokinase Aldolase G3P dehydrogenase Phosphoglycerate kinase Phosphoglyceromutase Enolase Pyruvate kinase Glycolysis: Net Gain Investment/ Return Step No. of ATPs gained No. of ATPs gained per glucose molecule Investment Glucose → Glucose-6phosphate -1 -1 Investment Fructose-6-phosphate → Fructose-1,6 -bisphosphate -1 -1 Return 1,3Bisphosphoglycerate → 3-Phosphoglycerate 1 2 Return Phosphoenolpyruvate → Pyruvate 1 2 Total © 2022, Aakash BYJU'S. All rights reserved. 2 Anaerobic Respiration Anaerobic respiration is a type of cellular respiration that occurs in the absence of oxygen in cytoplasm. Fermentation is the process of release of energy in an enzymatically controlled stepwise partial degradation of organic food (glucose) in the absence of O2. Anaerobic respiration Lactic acid fermentation © 2022, Aakash BYJU'S. All rights reserved. Alcoholic fermentation Anaerobic Respiration Ethyl alcohol fermentation Absence of O2 (In yeasts) Glucose (6-carbon molecule) In cytoplasm + CO2 + Energy Pyruvate (3-carbon molecule) Lack of O2 (In muscles) Lactic acid fermentation © 2022, Aakash BYJU'S. All rights reserved. Ethanol (2-carbon molecule) Lactic acid (3-carbon molecule) + Energy Lactic Acid Fermentation In lactic acid fermentation, incomplete oxidation of glucose takes place under anaerobic conditions by sets of reactions where pyruvic acid is converted to lactic acid without any release of CO2. NADH gives electrons and hydrogens to pyruvic acid. Lactate dehydrogenase Lactate (C3) Pyruvate (C3) NADH + H+ © 2022, Aakash BYJU'S. All rights reserved. NAD+ Alcoholic Fermentation Pyruvate decarboxylase catalyzes release of carbon dioxide from pyruvate and results in formation of acetaldehyde and carbon dioxide. Alcohol dehydrogenase, catalyzes oxidation of NADH to NAD+, on the cost of reduction of acetaldehyde to ethanol. Yeasts poison themselves to death when the concentration of alcohol reaches about 13%. Pyruvate (C3) Pyruvate decarboxylase Carbon dioxide (C1) © 2022, Aakash BYJU'S. All rights reserved. Acetaldehyde (C2) Alcohol dehydrogenase NADH + H+ Ethanol (C2) NAD+ Aerobic Respiration C6H12O6 Glucose 6O2 + Energy released Oxygen 6CO2 Carbon dioxide + 6H2O Water Aerobic respiration leads to a complete oxidation of organic substances in the presence of oxygen, and releases CO2, water and a large amount of energy present in the substrate. It is most common in higher organisms. © 2022, Aakash BYJU'S. All rights reserved. Aerobic Respiration In the mitochondria Oxidative decarboxylation Kreb’s cycle Electron Transport System (Oxidative Phosphorylation) Mitochondrial matrix Mitochondrial matrix Cristae (inner membrane) © 2022, Aakash BYJU'S. All rights reserved. Oxidative Decarboxylation A carboxyl group from pyruvate is removed to form CO2 – Decarboxylation. The 2-carbon molecule loses electrons ----> NAD+ to NADH – Oxidation. 2 carbon acetyl groups formed react with coenzyme A to form acetyl CoA. Cytosol Mitochondrion OC C NAD+ O Mg2+ O CH3 Pyruvate (end product of glycolysis) © 2022, Aakash BYJU'S. All rights reserved. 1 2 NADH+ Pyruvate dehydrogenase CO2 3 Coenzyme A S CoA C O CH3 Acetyl CoA Krebs Cycle The acetyl CoA then enters a cyclic pathway, Krebs’ cycle. It is also known as tricarboxylic acid cycle or citric acid cycle. It was elucidated by Hans Krebs. Krebs’ cycle starts with condensation of acetyl CoA with oxaloacetate in presence of a condensing enzyme citrate synthase to form a tricarboxylic, 6-carbon compound called citric acid. It is the 1st product of Krebs’ cycle and CoA is liberated. Pyruvic acid + 4NAD+ + FAD+ + 2H2O + ADP + Pi Mitochondrial matrix 3CO2 + 4NADH + 4H+ + FADH2 + ATP © 2022, Aakash BYJU'S. All rights reserved. Krebs Cycle Fatty acids Glucose Acetyl Coenzyme A Water Coenzyme A Citrate Citrate synthase Oxaloacetate Aconitase NADH Isocitrate Malate dehydrogenase NAD+ NAD+ Isocitrate dehydrogenase Malate NADH CO2 α - ketoglutarate Fumarase Water NAD+ Coenzyme A CO2 Fumarate Coenzyme A NADH Succi-Coenzyme A FADH2 Succinic dehydrogenase FAD Succinate GDP Succinyl-CoA synthetase GTP ATP © 2022, Aakash BYJU'S. All rights reserved. α – ketoglutarate dehydrgenase ADP ATP Yield 2x Glycolysis 2 ATP 2 NADH+H+ Pyruvate oxidation 2 NADH+H+ 2 ATP 2x Kreb’s cycle 6 NADH+H+ 2 FADH2 © 2022, Aakash BYJU'S. All rights reserved. 10 molecules of (NADH + H+ ) 2 molecules of FADH2 2 X Acetyl CoA CO2 Glucose is broken down to release CO2 and 4 molecules of ATP (2 in TCA cycle and 2 in glycolysis) are produced. Role of NADH and FADH2 NADH and FADH2 are: o Co-factors: They are non-protein chemical compounds or metallic ions that are required for the enzyme’s activity as a catalyst. o Electron carriers: Both carry two electrons per molecule from the earlier respiration processes. The electrons from NADH and FADH2 are donated to an electron acceptor. Transfer of electron occurs through a series of steps that are meant to create a lot of ATPs. © 2022, Aakash BYJU'S. All rights reserved. Electron Transport System The metabolic pathway through which the electron passes from one carrier to another, is called the electron transport system (ETS). Location: Inner membrane of the mitochondria. Components: o Complex I, II, III, IV - Help with electron transport o Complex V - Helps in synthesis of ATP © 2022, Aakash BYJU'S. All rights reserved. Complex I Complex I (NADH dehydrogenase) - It consists of 2 prosthetic groups o FMN (Flavin mononucleotide) o FeS (iron-sulphur complex) Here, NADH gives up the two electrons and gets oxidised to NAD+. These electrons (one by one) are passed on to FMN. It moves from FMN to the iron sulphur cluster that gets reduced from ferric ion (Fe3+) to ferrous ion ( Fe2+). UQ or ubiquinone is a mobile electron carrier closely associated with the complex I. o It carries 2 electrons (e-), 2 protons (H+) (taken from matrix) across to the next stage. © 2022, Aakash BYJU'S. All rights reserved. Complex II Complex II (Succinate dehydrogenase) consists of: o FAD (Flavin Adenine Dinucleotide) o FeS cluster UQ the mobile electron carrier is also present. Succinate, present in the matrix, transforms to fumarate in Krebs’ cycle and donates two electrons to complex II. FAD takes up both the electrons and hydrogen from succinate to become FADH2. These electrons then move to the iron sulphur cluster, reducing Fe3+ to Fe2+. Now FADH2 becomes FAD by losing the 2H+. UQ picks up the two electrons and 2H+ from matrix to become UQH2. © 2022, Aakash BYJU'S. All rights reserved. Complex III Complex III ( cytochrome bc1 complex) consists of o cytochrome b o (Fe-S) cluster o cytochrome c1 UQH2 arriving from complex I and II interacts with complex III, resulting in pumping of 4 protons into the intermembrane space. One by one, electrons move from Cyt b Fe-S Cyt c1. Cyt c is reduced by accepting electrons from Cyt c1. Cytochrome c is a small protein attached to the outer surface of the inner membrane. It acts as a mobile carrier for transfer of electrons between complex III and IV. © 2022, Aakash BYJU'S. All rights reserved. Complex IV Complex IV ( cytochrome c oxidase complex) consists of o cytochromes a and a3 o two copper centres One by one, two electrons move from Cyt c of Complex IV (CuA Cyta Cyta3 CuB) Further, two protons are pumped out into the intermembrane space. Also, two electrons are transferred to oxygen, which then binds with 2 H+ to yield water. © 2022, Aakash BYJU'S. All rights reserved. Complex V Complex V (ATP synthase) are coupled with complex I to IV when the electrons pass from one carrier to another. As the electrons are being transferred, the proteins pump hydrogen into the intermembrane space, creating an electrochemical gradient. This makes hydrogen pass through the ATP synthase. ATP synthase consists of two components: o F0: integral membrane protein complex that forms the channel for the passage of protons. o F1: peripheral membrane protein complex and a site for the synthesis of ATP from ADP and inorganic phosphate. © 2022, Aakash BYJU'S. All rights reserved. Outer side ATP 2H+ F0 Inner mitochondrial membrane F1 ADP Pi Matrix Complex V For each ATP produced, 2H+ pass through F0 from the intermembrane space to the matrix down the electrochemical proton gradient. e- e- NADH + H+ e- e- FADH2 © 2022, Aakash BYJU'S. All rights reserved. ETS ETS 3 ATP 2 ATP Electron Transport System The role of oxygen is limited to the terminal stage of the process. Yet, the presence of oxygen is vital, since it drives the whole process by removing hydrogen from the system. Oxygen acts as the final hydrogen acceptor. Unlike photophosphorylation, where it is the light energy that is utilised for the production of proton gradient required for phosphorylation, in respiration, the energy of oxidation-reduction is utilised for the same process. Hence, the process is called oxidative phosphorylation. © 2022, Aakash BYJU'S. All rights reserved. Electron Transport System Inter-membrane space Inner-mitochondrial membrane Matrix NADH + H+ 4H+ 2e- FMN (Fe-S) NAD+ e- Complex I (NADH dehydrogenase) I UQ e- e- UQH2 III 4H+ Cyt C1 Cyt b Fe-s Complex III (Cytochrome bc1) eCyt c Complex II (Succinate dehydrogenase) UQH2 UQ e- Succinate II (Fe-S) FAD Fumarate Cyt c e- IV Cu2 2H+ Cyta F0 Cu2 Cyta2 1 O2 + 2H+ 2 2H+ H2O Complex IV (Cytochrome c oxidase) ADP + Pi F1 ATP synthase ATP H+ + + + + © 2022, Aakash BYJU'S. All rights reserved. Electrochemical gradient - Respiratory Balance Sheet Expectation Reality Net ATP yield = 38 Net ATP yield = 32 Pathway operates in the following sequence: Glycolysis - TCA – ETS. All the pathways operate simultaneously. None of the pathway intermediates are used to synthesise any other compound. The entry and exit of molecules in cellular respiration can occur at any stage. They can be used to build other molecules. Transfer of NADH requires no energy. NADH produced during glycolysis needs to be transferred to mitochondria from cytoplasm, which requires 1 ATP/NADPH. Glucose is the only substrate. Other substrates might be used. © 2022, Aakash BYJU'S. All rights reserved. Respiratory Balance Sheet Anaerobic respiration Aerobic respiration Partial breakdown of glucose Complete breakdown of glucose into carbon dioxide and water Net gain of 2 ATP Net gain of 30-36 ATP NAD+ from NADH is formed slowly NAD+ from NADH is formed very fast © 2022, Aakash BYJU'S. All rights reserved. Amphibolic Pathway When energy is required, proteins or fatty acids are broken down to form acetyl-CoA and dihydroxyacetone phosphate which are incorporated into the Krebs’ cycle at their respective stages. This is catabolism. When the body requires fatty acids or proteins, respiratory pathway stops, and the same acetyl-CoA is utilised and fatty acids are manufactured. This process of synthesis is termed as anabolism. Hence the process is referred to as both catabolic and anabolic process respectively. Therefore, the respiratory pathway is considered to be an amphibolic pathway. © 2022, Aakash BYJU'S. All rights reserved. Amphibolic Pathway Respiratory pathways Substrates Fatty acids and glycerol Amino acids Building fats Building proteins Anabolic © 2022, Aakash BYJU'S. All rights reserved. Proteins Fats Amino acids Fatty acids and glycerol Respiratory substrates Respiratory pathways Catabolic Amphibolic Pathway Fats Carbohydrates Proteins Fatty acids and glycerol Simple sugars Ex: glucose Amino acids Glucose-6- phosphate Fructose-1, 6-bisphosphate Dihydroxyacetone phosphate ⇋ Glyceraldehyde-3-phosphate Pyruvic acid Acetyl CoA H2O © 2022, Aakash BYJU'S. All rights reserved. Krebs cycle CO2 Respiratory Quotient Respiratory quotient is the ratio of the volume of the carbon dioxide evolved to the volume of oxygen required for any respiratory substrate. The RQ ranges from 0 - 1. The knowledge about the RQ helps in identifying the respiratory substrate. RQ = Volume of CO2 evolved Volume of O2 consumed © 2022, Aakash BYJU'S. All rights reserved. Respiratory Quotient Respiratory quotient - Carbohydrates C6H12O6 + 6 O2 6 CO2+ 6H2O + ATP RQ = Respiratory quotient - Fats 2(C51H98O6) + 145 O2 102 CO2 + 98 H2O + ATP Respiratory quotient of proteins is about 0.9 © 2022, Aakash BYJU'S. All rights reserved. RQ = 6 CO2 6 O2 102 CO2 145 O2 =1 = 0.7 Respiratory Quotient Respiratory substrates Carbohydrates Fats Proteins RQ 1 0.7 0.9 Gross calorific value (kcal/g) 4.1 9.45 5.65 © 2022, Aakash BYJU'S. All rights reserved. Summary Cellular respiration Glycolysis Anaerobic respiration Lactic acid fermentation Alcoholic fermentation 1st step of cellular respiration Aerobic respiration Pyruvate oxidation Krebs’ cycle (Electron Transport System) Oxidative phosphorylation © 2022, Aakash BYJU'S. All rights reserved. Summary Glycolysis Step 1 Step 2 Step 3 Step 4 Step 5 Dihydroxyacetone phosphate (C3) Glucose (C6) Glucose6-phosphate (C6) ATP ADP Fructose6-phosphate (C6) Fructose- 1,6bisphosphate (C6) ATP ADP Preparatory stage © 2022, Aakash BYJU'S. All rights reserved. Glyceraldehyde3-phosphate (C3) Summary Step 5 Step 6 2Pi 2 x Pyruvate (Pyruvic acid) (C3) 2 x Phosphoenolpyruvate (C3) 2H2O Step 9 © 2022, Aakash BYJU'S. All rights reserved. 2 x 2 phosphoglycerate (C3) 2ADP 2ATP Step 8 Payoff stage 2 x 3-phosphoglyceric acid (C3) Step 7 2 x Triose phosphate 2 x 1,3-bisphosphoglyceric (Glyceraldehyde- 3acid phosphate) (C3) 2NAD+ 2 (NADH+H+) (C3) 2ADP 2ATP Summary Cytosol O2 Mitochondrion 2 NADH 2 NADH Glycolysis Glucose 2 Pyruvate 2 ATP © 2022, Aakash BYJU'S. All rights reserved. Krebs cycle Pyruvate oxidation Pyruvate 6 NADH 2 FADH2 Electron transport system and oxidative phosphorylation Acetyl CoA 2 ATP H2O CO2 32 ATP Summary GLYCOLYSIS– In cytoplasm Step #1 Mitochondria Matrix Inner membrane Mitochondrion © 2022, Aakash BYJU'S. All rights reserved. Krebs’ cycle takes place in the matrix of the mitochondria Step #2 Electron transport chain takes place in the inner membrane of the mitochondria Step #3 Summary Expectation Glycolysis 2 X Pyruvate oxidation 2 ATP 2 (NADH+H+) 2 (NADH+H+) 6 ATP 6 ATP 2 ATP 2X Krebs’ cycle 2 ATP 5 ATP 5 ATP 2 ATP 6 (NADH+H+) 18 ATP 15 ATP 2 FADH2 4 ATP 3 ATP 38 ATP 32 ATP Net yield: © 2022, Aakash BYJU'S. All rights reserved. Reality Summary Anaerobic respiration Aerobic respiration Partial breakdown of glucose. Complete breakdown of glucose into carbon dioxide and water. Net gain of 2 ATP. Net gain of 30-36 ATP. NAD+ from NADH is formed slowly. NAD+ from NADH is formed very fast. © 2022, Aakash BYJU'S. All rights reserved. Summary Respiratory pathways Substrates Fatty acids and glycerol Amino acids Building fats Building proteins Anabolic © 2022, Aakash BYJU'S. All rights reserved. Proteins Fats Amino acids Fatty acids and glycerol Respiratory substrates Respiratory pathways Catabolic