Respiration in Plants Class 11 Notes PDF: Comprehensive NEET Study Guide

01
Introduction to Respiration in Plants Class 11

Mastering respiration in plants class 11 notes pdf is essential for anyone aiming to crack NEET. While we often think of plants only as oxygen producers via photosynthesis, they are equally dependent on respiration for energy. Respiration is the biological oxidation of complex organic molecules (like glucose) to release energy in the form of ATP. This energy drives every cellular activity, from growth and nutrient uptake to reproduction. Unlike animals, plants do not have specialized respiratory organs, but every cell handles its own gas exchange—a unique survival strategy we will explore in detail.

OVERALL RESPIRATORY EQUATION
C6H12O6 + 6O2 → 6CO2 + 6H2O + Energy (ATP)
CELLULAR RESPIRATION Occurs 24/7 in every living cell. It is the molecular “burning” of food to harvest metabolic currency.
ENERGY CURRENCY ATP (Adenosine Triphosphate) provides the immediate energy for most cellular work.

02
Types of Respiration & Oxygen Usage

Respiration is categorized based on the availability of Oxygen. Understanding these two pathways is a high-yield part of your respiration in plants class 11 notes pdf study plan.

Feature Aerobic Respiration Anaerobic Respiration
Oxygen Presence Mandatory (O2 used) Absent (O2 not used)
End Products CO2, H2O, 36/38 ATP Ethanol/Lactic Acid, CO2, 2 ATP
Location Cytoplasm + Mitochondria Only Cytoplasm
Efficiency High (Complete oxidation) Low (Incomplete oxidation)
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03
Respiratory Quotient (RQ)

The Respiratory Quotient is the ratio of the volume of CO2 evolved to the volume of O2 consumed. It is a favorite topic for NEET MCQs as it reveals the nature of the respiratory substrate being used by the plant.

RQ FORMULA
RQ = (Volume of CO2 evolved) / (Volume of O2 consumed)
CARBOHYDRATES RQ = 1.0 (Glucose is completely oxidized).
FATS / PROTEINS RQ < 1.0 (e.g., Tripalmitin ≈ 0.7).
ORGANIC ACIDS RQ > 1.0 (e.g., Malic Acid ≈ 1.33).
ANAEROBIC RQ = ∞ (Infinity, as no O2 is consumed).

04
Glycolysis: The EMP Pathway

Glycolysis is the first stage of respiration and occurs in the Cytoplasm. It is common to both aerobic and anaerobic pathways. In your respiration in plants class 11 notes pdf, memorize the net gain and the end products of this 10-step enzymatic sequence.

  • Monomer: Glucose (6C).
  • End Product: 2 molecules of Pyruvic Acid (3C).
  • ATP Gain: Net 2 ATP (4 produced, 2 consumed).
  • Reduced Co-enzyme: 2 NADH2 molecules produced.
TIP
Sucrose is converted into glucose and fructose by the enzyme Invertase before entering the glycolytic pathway.

05
Fate of Pyruvate and Link Reaction

The path Pyruvate takes depends on the cellular conditions. Under aerobic conditions, it enters the mitochondrial matrix via the **Link Reaction** (Oxidative Decarboxylation).

LINK REACTION
Pyruvic Acid + CoA + NAD+ → Acetyl CoA + CO2 + NADH + H+

(Catalyzed by Pyruvate dehydrogenase complex.)

Anaerobic Pathway: Fermentation

In the absence of Oxygen, Pyruvate stays in the cytoplasm. In yeast, it forms Ethanol and CO2. In animal muscle cells (during exercise), it forms Lactic Acid. Both processes yield only 2 ATP per glucose molecule.

06
Krebs Cycle: Citric Acid Cycle

The Krebs Cycle occurs in the Mitochondrial Matrix. Acetyl CoA (2C) combines with Oxaloacetic Acid (4C) to form Citric Acid (6C). This cyclic pathway is the central hub of metabolism, as studied in any respiration in plants class 11 notes pdf.

OUTPUT PER PYRUVATE
3 NADH + 1 FADH2 + 1 GTP/ATP + 2 CO2

(Note: Per Glucose, these numbers are doubled.)

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07
Electron Transport System (ETS) & Oxidative Phosphorylation

This is the final stage of aerobic respiration, occurring on the Inner Mitochondrial Membrane (Cristae). Electrons from NADH and FADH2 are passed through a series of carriers to oxygen, releasing energy to pump protons and create a gradient.

FINAL ACCEPTOR Oxygen (O2) acts as the final electron acceptor, combining with H+ to form H2O.
ATP SYNTHASE Complex V utilizes the proton gradient (chemiosmosis) to synthesize ATP from ADP and iP.
WARN
1 NADH produces 3 ATP molecules, while 1 FADH2 produces only 2 ATP molecules because it enters the ETS later (at Complex II).

08
Amphibolic Pathway & Balance Sheet

Respiration is not just a catabolic (breakdown) process; it is Amphibolic. Many respiratory intermediates are withdrawn from the cycle to synthesize other biomolecules (Anabolism), such as fatty acids or amino acids.

Total Theoretical ATP Yield

Stage Reduced Co-enzymes Direct ATP Gain Total ATP (after ETS)
Glycolysis 2 NADH 2 ATP 8 ATP
Link Reaction 2 NADH 0 6 ATP
Krebs Cycle 6 NADH + 2 FADH2 2 GTP 24 ATP
Grand Total (Per Glucose) 38 ATP
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Quick Revision Summary

  • Glycolysis: Location: Cytoplasm; EMP pathway; net 2 ATP.
  • Fermentation: Partial breakdown; net only 2 ATP per glucose.
  • Krebs Cycle: Location: Mitochondrial Matrix; releases CO2.
  • ETS: Location: Inner Mitochondrial Membrane; uses O2.
  • Complex IV: Cytochrome c oxidase (contains copper).
  • Chemiosmosis: Proton gradient drives ATP synthesis via ATP synthase.
  • RQ: Carbohydrates (1), Fats (0.7), Organic Acids (>1).
  • Link Reaction: Converts Pyruvate into Acetyl CoA.
  • NADH vs FADH2: NADH gives 3 ATP; FADH2 gives 2 ATP.
  • Amphibolic: Pathway involving both breakdown and synthesis.
Download Respiration Notes (PDF)

09
Frequently Asked Questions

Why do plants not have a specialized respiratory system like lungs?
Plants do not need a specialized system because every part of the plant takes care of its own gas exchange. Gas requirements are low compared to animals, and most living cells are located close to the surface (e.g., in thin leaves or through lenticels in stems). Large spaces in the parenchyma also facilitate diffusion.
Explain why the Krebs Cycle is called the TCA Cycle.
TCA stands for Tricarboxylic Acid Cycle. It is named so because the first stable intermediate formed in the cycle, Citric Acid, contains three carboxylic acid (−COOH) groups.
What happens to the RQ when glucose is used for anaerobic respiration?
In anaerobic respiration, no Oxygen (O2) is consumed, but CO2 is still evolved (in alcoholic fermentation). Since RQ = CO2/O2, and O2 is zero, the RQ becomes infinity (∞).
What is oxidative phosphorylation?
It is the synthesis of ATP from ADP and inorganic phosphate using the energy released from the oxidation of reduced co-enzymes (NADH and FADH2) in the electron transport system. It is driven by a proton motive force.
Why is the theoretical yield of 38 ATP rarely achieved?
The yield of 38 ATP is a theoretical maximum. In reality, some energy is lost as heat, some protons leak across the membrane, and some intermediates are diverted into anabolic pathways (amphibolic nature). The actual yield is typically closer to 30-32 ATP.
What is the role of Complex IV in the ETS?
Complex IV (Cytochrome c oxidase) is the final enzyme of the electron transport chain. it receives electrons from cytochrome c and transfers them to Oxygen, which is then reduced to water. This complex contains two copper centers and two hemes (a and a3).

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Table of Contents — Biology Class 11

Table of Contents

Biology — Class 11

01The Living WorldGo to page
02Biological ClassificationGo to page
03Plant KingdomGo to page
04Animal KingdomGo to page
05Morphology of Flowering PlantsGo to page
06Anatomy of Flowering PlantsGo to page
07Structural Organisation in AnimalsGo to page
08Cell: The Unit of LifeGo to page
09BiomoleculesGo to page
10Cell Cycle and Cell DivisionGo to page
11Photosynthesis in Higher PlantsGo to page
12Respiration in PlantsGo to page
13Plant Growth and DevelopmentGo to page
14Breathing and Exchange of GasesGo to page
15Body Fluids and CirculationGo to page
16Excretory Products and their EliminationGo to page
17Locomotion and MovementGo to page
18Neural Control and CoordinationGo to page
19Chemical Coordination and IntegrationGo to page

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