Select Medium / माध्यम चुनें:

JAC • Class XI • Biology • Ch 12

Estimated Time: 45 Mins

Study Progress: In Progress

Respiration in Plants

In Class 11 Biology, "Respiration in Plants" provides an authoritative, curriculum-verified master resource aligned with the 2026–27 NCERT syllabus.

Take Chapter CBT Test View All Chapters

Overview Core Concepts Summary Self Check Take MCQ Test

🔥 Have You Ever Wondered?

How does a tiny microscopic cell break down glucose to generate 38 molecules of ATP without bursting into flames like an open fire? Cellular respiration dismantles chemical bonds in controlled steps across the cytoplasm and mitochondria.

Why This Chapter Matters

In Class 11 Biology, "Respiration in Plants" provides an authoritative, curriculum-verified master resource aligned with the 2026–27 NCERT syllabus.

Before You Begin (Prerequisites)

Mitochondria structure from Chapter 8.
Cellular respiration from Class 10.
ATP and energy currency.

What You Will Learn (Core Objectives)

Distinguish Aerobic respiration and Anaerobic respiration (Fermentation: Alcoholic vs Lactic acid).
Trace Glycolysis (EMP Pathway, 10 enzymatic steps in cytoplasm, net yield: $2\text{ ATP} + 2\text{ NADH}$).
Explain the Link Reaction: Oxidative decarboxylation of Pyruvate to Acetyl-CoA by Pyruvate Dehydrogenase.
Trace the Tricarboxylic Acid (TCA / Krebs) Cycle in the mitochondrial matrix.
Explain the Electron Transport System (ETS) and Oxidative Phosphorylation: Complexes I to V in inner mitochondrial membrane.
Calculate Respiratory Quotient (RQ): Carbohydrates ($1.0$), Fats ($0.7$), Proteins ($0.9$).

Chapter Roadmap & Progression

1 1. Glycolysis (EMP Pathway)

2 2. The Krebs Cycle (TCA Cycle)

3 3. Electron Transport System (ETS)...

Complete Concept Guide (100% Curriculum Coverage)

1. Glycolysis (EMP Pathway)

Discovered by Embden, Meyerhof, and Parnas. Occurs in the cytoplasm of all living cells (anaerobic, requires zero oxygen):
• 1 Glucose ($6C$) is phosphorylated and cleaved into two molecules of Pyruvate ($3C$).
• Key regulatory enzyme: Phosphofructokinase (PFK).
• Net Yield: Consumes 2 ATP; produces 4 ATP → Net $+2\text{ ATP}$ and $+2\text{ NADH}$.

2. The Krebs Cycle (TCA Cycle)

Inside the mitochondrial matrix:
• Link Reaction: $\text{Pyruvate} + \text{CoA} + \text{NAD}^+ \xrightarrow{\text{PDH}} \text{Acetyl-CoA} + \text{CO}_2 + \text{NADH}$.
• TCA Cycle: $2C$ Acetyl-CoA condenses with $4C$ Oxaloacetate to form $6C$ Citric acid. Per glucose (2 turns): produces $\mathbf{6\text{ NADH} + 2\text{ FADH}_2 + 2\text{ GTP/ATP} + 4\text{ CO}_2}$!

3. Electron Transport System (ETS) & RQ

In the inner mitochondrial membrane, electrons from NADH and $\text{FADH}_2$ cascade through Complexes I to IV to the final electron acceptor: Oxygen (forming $\text{H}_2\text{O}$)! Protons pumped into the intermembrane space drive Complex V (ATP Synthase):
• $1\text{ NADH} \implies 3\text{ ATP}$ (or $2.5\text{ ATP}$).
• $1\text{ FADH}_2 \implies 2\text{ ATP}$ (or $1.5\text{ ATP}$).
• Respiratory Quotient: $\mathbf{RQ = \frac{\text{Volume of } \text{CO}_2 \text{ evolved}}{\text{Volume of } \text{O}_2 \text{ consumed}}}$.

Respiration in Plants - Key Biological & Anatomical Model

Chapter Summary & 10 Key Takeaways

Takeaway 1

EMP Glycolytic Cascade: Cytoplasmic anaerobic breakdown producing 2 net ATP and 2 NADH.

Takeaway 2

Link Reaction: Mitochondrial gateway converting pyruvate to acetyl-CoA and releasing CO2.

Takeaway 3

Krebs Cycle: Matrix enzymatic furnace producing reducing power equivalents NADH and FADH2.

Takeaway 4

Complex V ATP Synthase: Rotary nanomachine harnessing intermembrane proton motive force.

Takeaway 5

Respiratory Quotient (RQ): Gas exchange volumetric ratio diagnosing metabolised fuel substrate.

Check Your Understanding (Diagnostic Practice Questions)

Diagnostic questions testing core conceptual clarity. Answers are hidden initially — solve each problem first, then click to reveal the step-by-step verified solution.

Trace the sequential enzymatic reactions of Glycolysis (EMP Pathway). What is the net yield of ATP and NADH?

Reveal Answer & Explanation

Answer: Ten reactions in cytoplasm: Glucose is phosphorylated to Glucose-6-phosphate by hexokinase → isomerized to Fructose-6-phosphate → phosphorylated to Fructose-1,6-bisphosphate → cleaved into DHAP and PGAL → oxidized to 1,3-bisphosphoglycerate → dephosphorylated to 3-phosphoglycerate → 2-phosphoglycerate → PEP → Pyruvate. Net yield: 2 ATP and 2 NADH per glucose molecule.
10-step cytoplasmic cascade; net yield of 2 ATP and 2 NADH per glucose.

What is the final electron acceptor in aerobic cellular respiration? What product is formed?

Reveal Answer & Explanation

Answer: Molecular Oxygen ($O_2$) is the terminal electron acceptor at Complex IV (Cytochrome c oxidase) of the electron transport system. It combines with protons ($H^+$) and electrons to form metabolic Water ($\text{H}_2\text{O}$).
Oxygen is the terminal electron acceptor, forming water.

Define Respiratory Quotient (RQ). Calculate the RQ value for: (i) Glucose, (ii) Tripalmitin (fat).

Reveal Answer & Explanation

Answer: RQ is the ratio of the volume of $\text{CO}_2$ evolved to the volume of $O_2$ consumed during cellular respiration: $RQ = \frac{\text{Volume of CO}_2}{\text{Volume of O}_2}$. (i) For glucose: $\text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2 \to 6\text{CO}_2 + 6\text{H}_2\text{O} \implies RQ = 6/6 = 1.0$. (ii) For tripalmitin: $2\text{C}_{51}\text{H}_{98}\text{O}_6 + 145\text{O}_2 \to 102\text{CO}_2 + 98\text{H}_2\text{O} \implies RQ = 102/145 = 0.7$.
RQ = CO2 / O2; Glucose = 1.0, Tripalmitin = 0.7.

Why is the Krebs cycle also called the Amphibolic pathway?

Reveal Answer & Explanation

Answer: Because it is involved in both catabolism (breakdown of carbohydrates, fats, and proteins to release energy) and anabolism (intermediates like $\alpha$-ketoglutarate, oxaloacetate, and succinyl-CoA are constantly withdrawn for synthesizing amino acids, fatty acids, and chlorophyll).
Serves dual roles in both catabolic breakdown and anabolic synthesis.

What is the major difference between Fermentation and Aerobic Respiration regarding energy release and NADH oxidation?

Reveal Answer & Explanation

Answer: Fermentation is an anaerobic partial breakdown of glucose yielding only 2 ATP with slow oxidation of NADH to $\text{NAD}^+$ without an ETS; Aerobic respiration is complete oxidation of glucose to $\text{CO}_2$ and $\text{H}_2\text{O}$ yielding 36-38 ATP with rapid, vigorous oxidative phosphorylation through an electron transport system.
Partial oxidation with 2 ATP (Fermentation) vs complete oxidation with 36-38 ATP (Aerobic).

Finished Studying This Chapter?

READY TO PRACTICE?

Timed CBT Practice Tests (Exam Simulator)

Put your concepts to the test with official curriculum-aligned Foundation and Advanced practice tests. Get instant accuracy scores, time metrics, and step-by-step verified explanations.

Foundation Test

15 MCQs • Core Concepts

Advanced Test

15 MCQs • HOTS & Traps