CBSE Class 11 Biology Respiration in Plants PDF

# CBSE Quick Revision Notes ## Class - 11, Biology ### Chapter - 14, Respiration in Plants Respiration is an energy-releasing, enzyme-controlled catabolic process that involves the stepwise oxidative breakdown of food substances inside living cells. **C6H12O6+ 6O2 → 6CO2 + 6H2O + Energy** * Livin...

# CBSE Quick Revision Notes ## Class - 11, Biology ### Chapter - 14, Respiration in Plants Respiration is an energy-releasing, enzyme-controlled catabolic process that involves the stepwise oxidative breakdown of food substances inside living cells. **C6H12O6+ 6O2 → 6CO2 + 6H2O + Energy** * Living organisms require energy for all activities like absorption, movement, reproduction, or even for breathing. The required energy is obtained from the oxidation of food during respiration. * Cellular respiration is the process that involves the breakdown of food substances present within the cell to release energy for ATP synthesis. * Complex molecules break down in the cytoplasm and mitochondria to generate energy. * The breakdown of complex compounds through oxidation in the cell is called respiration. * The substances that get oxidized are called substrates. * The energy released during oxidation is not directly used but is used for ATP synthesis, which can be broken down when energy is required. This is why ATP is called the energy coin of the cell. * Respiration requires oxygen. Oxygen is taken in through stomata, lenticels, and root hairs in plants. * Plants can perform respiration without respiratory organs because: 1. Every part of the plant takes care of its own gas exchange requirements. 2. Plants do not have a high demand for gas exchange. 3. The distance for gas exchange is not very long for large plants. 4. During photosynthesis, O2 is released in leaves and diffuses to other parts of the plant. * During respiration, oxygen is used and carbon dioxide and water are released along with energy molecules in the form of ATP. * The respiratory quotient is the ratio of the volume of carbon dioxide released to the volume of oxygen absorbed during respiration. The RQ value is equal to 1 for carbohydrates, less than 1 for proteins, and more than 1 for fats. ## Aerobic Versus Anaerobic Respiration Aerobic respiration is an enzyme-controlled release of energy from a substrate in the form of ATP, which involves the complete oxidation of the substrate in the presence of oxygen. Anaerobic respiration is an energy-releasing process where the complete breakdown of the substrate does not occur because of the lack of oxygen. ## Types of Respiration ### Glycolysis * Glycolysis scheme was given by Gustaf Embden, Otto Meyerhof, and J. Parnas. It is also called the EMP pathway. * Glycolysis is the partial oxidation of glucose or similar hexose sugars in the cytoplasm to form two molecules of pyruvic acid with the release of some ATP and NADH2. This occurs in the cytoplasm. * In plants, glucose is obtained from sucrose or storage carbohydrates. Sucrose is converted to glucose and fructose by the enzyme invertase. * Glycolysis starts with the phosphorylation of glucose by the enzyme hexokinase to form glucose-6-phosphate. This process uses one molecule of ATP. * In the following step, glucose-6-phosphate is converted to fructose-6-phosphate, catalyzed by the enzyme phosphohexose isomerase. * Fructose-6-phosphate uses another molecule of ATP to form fructose-1,6-biphosphate, facilitated by the enzyme phosphofructokinase. * During glycolysis, two molecules of ATP are used to form fructose-1,6-biphosphate from glucose. The oxidation of glyceraldehyde-3-phosphate results in forming two molecules of NADPH2. Each NADH is equivalent to 3 ATP, making the net gain of ATP in glycolysis four. * Pyruvic acid is the main product of glycolysis. The further breakdown of pyruvic acid depends on the requirement of the cell. * In animal cells, such as muscles during exercise when oxygen becomes insufficient, pyruvic acid is converted to lactic acid by the enzyme lactate dehydrogenase due to the reduction of NADH2. * In yeast, during fermentation, pyruvic acid is converted into ethanol and CO2. The enzymes involved are pyruvic acid decarboxylase and alcohol dehydrogenase, which catalyze the reaction. * Both lactic acid and alcoholic fermentation yield very little energy. * If the alcohol concentration exceeds 13%, yeast will poison itself. * The final product of glycolysis, pyruvate, is transported from the cytoplasm to the mitochondria for further breakdown. * The oxidation of pyruvate to Acetyl-CoA is done by the liberation of CO2 and NADH. The reaction needs several coenzymes along with NAD+ and is catalyzed by pyruvate dehydrogenase. **Pyruvic acid + CoA + NAD + → Acetyl CoA + CO2** **+ NADH + H + Mg** * Acetyl CoA enters the TCA cycle or Krebs cycle. ### TCA Cycle/Krebs Cycle * The TCA cycle was discovered in 1940 by Hans Krebs. It is called the TCA cycle due to the primary product being citric acid. * Acetyl CoA combines with OAA (oxaloacetic acid) and water with the release of CoA to form citric acid via the enzyme citrate synthase. * Citrate is then isomerized to isocitrate. It goes through two subsequent steps of decarboxylation, leading to the formation of α-ketoglutarate and then succinyl-CoA. * In the remaining steps, succinyl-CoA is oxidized to OAA, which keeps the cycle going. * There are three points in the cycle where NAD+ is reduced to NADH2, and one point where FAD+ is reduced to FADH2. * One molecule of glucose yields two molecules of pyruvate during glycolysis. These two molecules of pyruvate generate 2 ATP, 8 NADH2, and 2 FADH2 in the Krebs cycle. **Matrix Pyruvic + 4NAD+ + FAD + 2H2O + ADP + Pi → 3CO2+ 4NADH+ 4H + FADH ATP** ### Electron Transport Chain * The pathway by which electrons are transported from one carrier to another within the inner mitochondrial membrane is called ETC (Electron Transport Chain). * The ETC works by transferring electrons from NADH and FADH2. The electrons then pass through the chain of carriers, which are the cytochromes. * The flow of electrons through the electron transport chain is associated with the pumping of protons (H+) from the matrix to the intermembrane space, establishing an electrochemical gradient. The energy is used in creating ATP. * The energy released by the electron transport chain is used for the synthesis of ATP from ADP and inorganic phosphate. The number of ATP molecules produced depends on the electron donor. * The oxidation of one molecule of NADH forms 3 molecules of ATP, while the oxidation of one molecule of FAD₂ forms 2 molecules of ATP. ### Oxidative Versus Photophosphorylation * **Oxidative phosphorylation**: * It occurs in the respiratory process. * The proton gradient that is required for phosphorylation is generated by the oxidation-reduction energy. * **Photophosphorylation**: * It occurs in photosynthesis. * The proton gradient is generated by light energy. ### ATP Synthetase * ETC provides energy that is used by ATP synthase for the production of ATP. It is composed of two main parts: F1 and FO. * F1 is a peripheral membrane protein complex where the site for ATP synthesis from ADP and inorganic phosphate is located. FO is an integral membrane protein that creates a channel for protons. * For every ATP produced, 2H+ move from the intermembrane space to the matrix through FO, down the electrochemical gradient. ## Fermentation Fermentation refers to the incomplete breakdown of glucose molecules in the absence of oxygen. * Fermentation is responsible for the incomplete oxidation of glucose. * During fermentation, only two molecules of ATP are gained. * NADH is slowly oxidized to NAD+ during fermentation. ## Aerobic Respiration * Aerobic respiration is responsible for the complete oxidation of glucose. * During aerobic respiration, more ATP is gained. * NADH is rapidly oxidized to NAD+ during aerobic respiration. ## Amphibolic Pathway * Glucose is the most preferred substrate for respiration. All carbohydrates are usually converted into glucose before they are used. * Fats are broken down into glycerol and fatty acids, which are further broken down into Acetyl CoA and enter the respiratory pathway. * Proteins are broken down into amino acids, which further enter the Krebs cycle. * The breaking down processes in organisms are called catabolism and the building up processes are called anabolism. Hence, respiration is an amphibolic pathway.