NCERT Class 11 Biology Chapter 14 Notes Respiration In Plants - Download PDF Notes

The respiration in plants is a very important chapter of the NCERT respiration in plants from an exam point of view. The NCERT Class 11 Biology Chapter 14 notes give you a basic idea of the chapter on respiration in plants. The main topics covered in NCERT Class 11 Biology notes are definitions, do plants breathe, the process of glycolysis, fermentation, aerobic respiration, the tricarboxylic acid cycle (TCA, also known as the Krebs cycle or the citric acid cycle), the electron transport system (ETS), oxidative phosphorylation, the respiratory balance sheet, the amphibolic pathway, and respiratory quotient. Download the CBSE Notes for Class 11 Biology, Chapter 14, PDF to use it offline anywhere. Students must go through each topic of respiration in plants in Class 11 Notes Biology in the easiest and most effective way possible with the help of NCERT Notes for Class 11.

Class 11 Biology chapter 14 notes also cover all the important concepts related to this chapter, which are useful in various competitive exams. Respiration in plants NCERT Notes for Class 11 Biology help you revise all these major concepts given in the NCERT Book in a short period of time during CBSE Board exam preparation. CBSE Class 11 Biology Chapter 14 notes will help you with quick revision. The Respiration In Plants chapter covers all headings of NCERT. CBSE Class 11 Biology chapter 14 notes also contain important examples that have been frequently asked in the various exams. Having revision notes and NCERT Solutions for Class 11 Biology Chapter 14 handy is beneficial to save you time. The NCERT Class 11 notes pdf can be downloaded through the link given below.

Also, students can refer,

• NCERT Solutions for Class 11 Biology Chapter 14 Respiration in Plants
• NCERT Exemplar Class 11 Biology Chapter 14 Solutions Respiration in Plants

NCERT Class 11 Chapter 14 Class Notes

Respiration In Plants

Definition of Respiration: It is defined as the breaking of C-C bonds of complex compounds within cells by oxidation, resulting in the release of a significant amount of energy. Respiratory substrates refer to the molecules that are oxidized during this process.

• Class 11 Biology Chapter 14 notes will teach you about the breathing process in plants.
• Respiration in Plants Class 11 notes deal with the mechanism of cellular respiration, or the breakdown of dietary components within the cell to release energy, and the trapping of this energy for ATP synthesis.
• According to notes for Class 11 Biology chapter 14 Plants, like the majority of other species on the planet, utilize oxygen to breathe.
• Plants, on the other hand, do not have organs devoted to gaseous exchange; therefore they do not breathe as most animals do. Instead, they use stomata and lenticels, which are organelles that function in this way.
• Photosynthesis occurs in chloroplasts (only in eukaryotes), while the breakdown of complex molecules to produce energy occurs in the cytoplasm and mitochondria (only in eukaryotes).

Do Plants Breathe?

• Plants do not have specialized organs for gaseous exchange, unlike animals, but they do have stomata and lenticels for this purpose.
• Plants can survive without having respiratory organs for a variety of reasons. To begin with, each plant component is responsible for its own gas exchange requirements. Gases are rarely transported from one component of the plant to another. Second, there aren't many gas exchange requirements in plants.
• Roots, stems, and leaves breathe at a far slower rate than animals.
• Large amounts of gases are transferred only during photosynthesis and each leaf is highly adapted to meet its individual needs at this time. Because O₂ is released within the cell when cells photosynthesize, the availability of O₂ is not an issue. Third, even in huge, bulky plants, the distance that gases must diffuse is small.
• A plant's live cells are all near to the plant's surface. At least a portion of the surface of most plant cells is in contact with air. The loose packing of parenchyma cells in leaves, stems, and roots, which create an interconnected network of air gaps, also helps.
• The complete combustion of glucose, which produces CO₂ and H₂O as end products, generates a large amount of energy, the majority of which is released as heat.
• If this energy is to be beneficial to the cell, it must be able to be used to synthesize additional molecules. The plant cell's aim is to catabolize the glucose molecule in such a way that not all of the released energy is released as heat. The objective is to oxidize glucose in short steps so that the energy released can be coupled to ATP synthesis.
• Oxygen is used in the process of respiration, and carbon dioxide, water, and energy are released as products. The combustion reaction necessitates the use of oxygen.
• However, some cells exist where oxygen might not be accessible.
• Anaerobic respiration is cellular respiration that occurs without the need for oxygen. Some of these organisms are facultative anaerobes, whereas others are obligate anaerobes. In any event, all living organisms retain the enzymatic machinery needed to partially oxidize glucose without oxygen.
• The breakdown of glucose into pyruvic acid is referred to as glycolysis.

Glycolysis

• It is the sole method of respiration in anaerobic species. Glycolysis is a process that happens in the cytoplasm of all living organisms. Glucose is partially oxidized to produce two molecules of pyruvic acid in this reaction. This glucose comes from either the end product of photosynthesis, sucrose, or stored carbohydrates in plants. The enzyme invertase converts sucrose into glucose and fructose, and these two monosaccharides easily enter the glycolytic pathway.
• Hexokinase is an enzyme that phosphorylates glucose and fructose to produce glucose-6-phosphate. This phosphorylated glucose isomerizes to fructose-6-phosphate. The following steps in glucose and fructose metabolism are identical. A cascade of ten processes takes place in glycolysis to produce pyruvate from glucose, all of which are controlled by various enzymes.
• ATP is used in two steps: the first is when glucose is converted to glucose 6-phosphate, and the second is when fructose 6-phosphate is converted to fructose 1, 6-bisphosphate.
• Dihydroxyacetone phosphate and 3-phosphoglyceraldehyde (PGAL) are formed from fructose 1, 6-bisphosphate.
• NAD+ is transformed to NADH + H+ in one step, when 3-phosphoglyceraldehyde (PGAL) is converted to 1, 3-bisphosphoglycerate (BPGA).
• Two redox-equivalents from PGAL are transferred to a molecule of NAD+. To convert PGAL to BPGA, it is oxidized and combined with inorganic phosphate.
• The energy produced by the conversion of BPGA to 3-phosphoglyceric acid (PGA) is trapped by the production of ATP. During the conversion of PEP to pyruvic acid, another ATP is synthesized.
• The primary product of glycolysis is pyruvic acid. Pyruvate's metabolic fate is determined by cellular needs.
• Different cells handle pyruvic acid produced by glycolysis in three ways. Lactic acid fermentation, alcoholic fermentation, and aerobic respiration are the three types. Many prokaryotes and unicellular eukaryotes ferment under anaerobic circumstances.
• However, organisms need Krebs' cycle, commonly known as aerobic respiration, to complete the oxidation of glucose to CO₂ and H₂O.

The Steps of Glycolysis

Fermentation

• Under anaerobic conditions, incomplete oxidation of glucose is performed by a series of processes in which pyruvic acid is transformed to CO₂ and ethanol, for example, in yeast fermentation. These processes are catalyzed by enzymes, pyruvic acid decarboxylase and alcohol dehydrogenase. Some bacteria, for example, convert pyruvic acid to lactic acid.
• Lactate dehydrogenase converts pyruvic acid to lactic acid when oxygen is insufficient for cellular respiration in animal cells, such as muscles during exercise. The reducing agent in both processes is NADH + H+, which is re-oxidized to NAD+.
• In both lactic acid and alcohol fermentation, only around 7% of the energy in glucose is released, and not all of it is locked as high-energy ATP bonds. Furthermore, the processes are harmful since they produce either acid or alcohol.
• Aerobic respiration is a process in which organic compounds are completely oxidized in the presence of oxygen, releasing CO₂, water, and a considerable quantity of energy from the substrate. Higher organisms are the most typical users of this sort of respiration.

Aerobic Respiration

Pyruvate, the last result of glycolysis, is carried from the cytoplasm into the mitochondria in order for aerobic respiration to occur.

The following are critical events in aerobic respiration:

• The full oxidation of pyruvate by removing all hydrogen atoms one at a time, leaving three molecules of CO₂.
• The electrons extracted as part of the hydrogen atoms are transferred to molecular O₂ while ATP is synthesized at the same time.
• The first step occurs in the mitochondria's matrix, while the second occurs on the mitochondria's inner membrane.
• Pyruvate, which is produced in the cytosol by glycolytic catabolism of carbohydrates, enters the mitochondrial matrix and is oxidatively decarboxylated by pyruvic dehydrogenase in a complex series of events. Several coenzymes, notably NAD+ and Coenzyme A, are required for pyruvic dehydrogenase to catalyze processes.

Pyruvic acid + CoA + NAD+ Mg₂+pyruvate dehydrogenase→ Acetyl CoA + CO₂ + NADH + H+

• During this process, two molecules of NADH are formed from the metabolism of two molecules of pyruvic acid.
• The acetyl CoA then enters a cyclic route known as the tricarboxylic acid cycle, or Krebs' cycle after the scientist Hans Krebs, who discovered it.

Tricarboxylic Acid Cycle (TCA): The Krebs Cycle or The Citric Acid Cycle

• To produce citric acid, the TCA cycle begins with the condensation of the acetyl group with oxaloacetic acid (OAA) and water. A molecule of CoA is released as a result of the process, which is catalyzed by the enzyme citrate synthase.
• The isomerization of citrate to isocitrate occurs next. It is subsequently followed by two decarboxylation processes, which result in the synthesis of -ketoglutaric acid and succinyl-CoA. Succinyl-CoA is oxidized to OAA in the remaining phases of the citric acid cycle, allowing it to continue.
• A molecule of GTP is produced during the conversion of succinyl-CoA to succinic acid. This is phosphorylation at the level of the substrate.
• GTP is transformed to GDP while ATP is synthesized from ADP in a coupled reaction.
• NAD+is reduced to NADH + H+ at three stages in the cycle, and FAD+is converted to FADH2 at one point.
• The ongoing oxidation of acetyl CoA via the TCA cycle necessitates the replenishment of the cycle's first member, oxaloacetic acid.
• It also necessitates NAD+and FAD+regeneration from NADH and FADH2, respectively.
• The following is a summary equation for this phase of respiration:

Pyruvic acid + 4NAD+ + FAD++2H₂O+ADP+Pi Mitochondrial Matrix→ + 3CO₂ + 4NADH + 4H+ + FADH₂ + ATP

• In the TCA cycle, glucose is been broken down to liberate CO₂ and eight molecules of NADH + H+; two molecules of FADH2 and only two molecules of ATP are produced.

Electron Transport System (ETS) and Oxidative Phosphorylation

• The energy held in NADH + H+ and FADH2 is released and used in the respiratory process. This is achieved by oxidizing them via the electron transport system, where the electrons are transferred to O₂, resulting in the creation of H₂O.
• The electron transport system (ETS) is a metabolic route located in the inner mitochondrial membrane that allows electrons to go from one carrier to another.
• During the citric acid cycle, electrons from NADH generated in the mitochondrial matrix are oxidized by a NADH dehydrogenase (complex I), and electrons are then transported to ubiquinone situated within the inner membrane.
• Ubiquinone also acquires reducing equivalents from the citric acid cycle via FADH2 (complex II), which is produced during the oxidation of succinate.
• The reduced ubiquinone (ubiquinol) is next oxidized by the cytochrome bc1 complex, which transfers electrons to cytochrome c. (complex III).
• Cytochrome c is a tiny protein that is linked to the inner membrane's outer surface and serves as a mobile carrier for electron transport between complex III and IV.
• Complex IV is a cytochrome c oxidase complex that contains two copper centres, as well as cytochromes a and a₃.
• As electrons migrate from one carrier to another in the electron transport chain via complex I to IV, they are coupled to ATP synthase (complex V) for the synthesis of ATP from ADP and inorganic phosphate.
• The amount of ATP produced is determined by the electron donor's type.
• When one molecule of NADH is oxidized, three molecules of ATP are produced, however, when one molecule of FADH₂ is oxidized, only two molecules of ATP are produced.
• Despite the fact that the aerobic process of respiration occurs exclusively in the presence of oxygen, oxygen's significance in the process is restricted.
• The ultimate hydrogen acceptor is oxygen. In contrast to photophosphorylation, where light energy is used to produce the proton gradient required for phosphorylation, the energy of oxidation-reduction is used for the same process in respiration. This is why the process is known as oxidative phosphorylation.
• With the help of ATP synthase (complex V), the energy released during the electron transport system is used to synthesize ATP. This complex is made up of two major components: F₁ and F₀. The F₁ headpiece is a peripheral membrane protein complex that includes a site for ATP production from ADP and inorganic phosphate.
• F₀ is an important membrane protein complex that creates the channel through which protons penetrate the inner membrane, The transport of protons via the channel is coupled to the catalytic site of the F₁ component for the synthesis of ATP. For each ATP produced, 4H⁺ flows via F₀ from the intermembrane space to the matrix along the electrochemical proton gradient.

The Respiratory Balance Sheet

The net gain of ATP for each glucose molecule oxidized can be calculated. These calculations are only possible if certain assumptions are met:

• There is a sequential, ordered pathway in operation, with one substrate creating the next and glycolysis, TCA cycle, and ETS pathway following one after the other.

• The NADH produced during glycolysis is transported to the mitochondria and undergoes oxidative phosphorylation.

• None of the pathway's intermediates are used to make any other chemical.

• At any of the intermediate stages, only glucose is respired; no other potential substrates enter the route.

Comparison Between Fermentation and Aerobic Respiration

• Glucose is only partially broken-down during fermentation, whereas it is completely broken down during aerobic respiration to CO₂ and H₂O.

• Fermentation yields only two molecules of ATP for every molecule of glucose degraded to pyruvic acid, whereas aerobic conditions yield many more molecules of ATP.

• In fermentation, NADH is oxidized to NAD+ slowly, but in aerobic respiration, the reaction is very fast.

Amphibolic Pathway

• The amphibolic pathway is involved in both catabolism (breakdown) and anabolism (building up).
• Respiratory pathways are mostly catabolic processes that provide energy to the biological system.
• The respiratory route generates a variety of intermediates.
• Many of them are used as starting materials for both primary and secondary metabolite production.
• Acetyl-CoA is required for the production of fatty acids, aromatic chemicals, steroids, terpenes, and carotenoids in addition to the Krebs cycle.

Respiratory Quotient

• The respiratory quotient (RQ) or respiratory ratio, refers to the ratio between the volume of CO₂ evolved and the volume of O₂ consumed in respiration.

RQ=Volume of CO₂ evolved /Volume of O₂ consumed

• The type of respiratory substrate used during respiration determines the respiratory quotient.
• Because equal amounts of CO₂ and O₂ are evolved and consumed, the RQ will be 1 when carbohydrates are utilized as a substrate and are totally oxidized, as illustrated in the equation below:

C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + Energy

RQ = 6CO₂ / 6O₂ = 1.0

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This Respiration in Plants Class 11 notes will help you review the chapter and have a better understanding of the main themes addressed. These Notes for Class 11 Biology Chapter 14 are also beneficial for covering the main themes of the CBSE Biology Syllabus in Class 11 as well as for competitive exams such as AIPMT, AIIMS, NEET, and others. The Class 11 Biology chapter 14 notes pdf download can be utilized for offline preparation.

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