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Respiration in Plants

NCERT Class 11 Biology Chapter 12

Respiration in Plants for Class 11 Biology and NEET: glycolysis, fermentation, Krebs’ cycle, electron transport, ATP yield, amphibolic pathway and RQ.

7 topics Updated 8 Nov 2026

For: Class 11 and NEET

In the syllabus: NEET Class 11 syllabus

With your textbook

NCERT Biology (Class 11), Chapter 12 “Respiration in Plants”, reprint 2026-27.

Open the official NCERT chapter (PDF, 1.7 MB, ncert.nic.in)

Checked on 19 Oct 2026.

Learn in this order

  1. Respiration and gas exchange in plants

    Definition, respiratory substrates, ATP as energy currency, stomata and lenticels.

    NCERT Section 12.1 11 min read 6 solved examples 6 practice questions

  2. Glycolysis

    The EMP pathway steps with a diagram, where ATP and NADH are used and made, the net gain of 2 ATP, and pyruvate’s fates.

    NCERT Section 12.2 11 min read 5 solved examples 7 practice questions

  3. Fermentation

    Alcoholic fermentation in yeast, lactic acid fermentation in muscle, enzymes and net ATP.

    NCERT Section 12.3 9 min read 5 solved examples 6 practice questions

  4. Aerobic respiration: Krebs’ cycle and ETS

    The link reaction, Krebs’ (TCA) cycle, electron transport chain and ATP synthase, with diagrams.

    NCERT Section 12.4 15 min read 5 solved examples 9 practice questions

  5. The respiratory balance sheet: 38 ATP

    ATP from one glucose (NCERT’s net 38), its assumptions, and aerobic and anaerobic respiration compared.

    NCERT Section 12.5 11 min read 5 solved examples 9 practice questions

  6. Amphibolic pathway: fats and proteins in respiration

    How fats and proteins enter respiration, catabolism vs anabolism, and why the respiratory pathway is amphibolic.

    NCERT Section 12.6 8 min read 4 solved examples 7 practice questions

  7. Respiratory quotient (RQ)

    The formula, RQ of carbohydrates and fats worked out, and RQ of proteins, organic acids and fermentation.

    NCERT Section 12.7 9 min read 6 solved examples 8 practice questions

Key formulas in this chapter

Do plants breathe?

  • CHO + 6O → 6CO + 6HO + energy
  • energy currency of the cell: ATP
  • gas exchange in plants: stomata and lenticels

Glycolysis

  • glucose (6C) → 2 pyruvic acid (3C)
  • ATP: 4 made − 2 used = net 2 per glucose
  • per glucose: 2 NADH + 2H

Fermentation

  • yeast: pyruvic acid → ethanol + CO
  • muscle, some bacteria: pyruvic acid → lactic acid
  • net gain: 2 ATP per glucose
  • energy released: less than 7 per cent of that in glucose

Aerobic respiration

  • pyruvic acid + CoA + NAD → acetyl CoA + CO + NADH + H
  • per glucose (matrix): 6 CO, 8 NADH, 2 FADH, 2 ATP
  • NADH → 3 ATP; FADH → 2 ATP
  • 4 H through F per ATP

The respiratory balance sheet

  • NCERT model: NADH → 3 ATP; FADH → 2 ATP
  • glycolysis: 2 ATP + 2 NADH = 8 ATP
  • pyruvate → acetyl CoA: 2 NADH = 6 ATP
  • Krebs’ cycle: 2 ATP + 6 NADH + 2 FADH = 24 ATP
  • net gain: 8 + 6 + 24 = 38 ATP per glucose
  • fermentation: net 2 ATP per glucose

Amphibolic pathway

  • carbohydrates → monosaccharides → glycolysis
  • fats → glycerol (DHAP ↔ PGAL) + fatty acids (acetyl CoA)
  • proteins → amino acids → pyruvate, acetyl CoA or Krebs’ cycle
  • catabolism: breaking down; anabolism: synthesis
  • amphibolic pathway: used in both catabolism and anabolism

Respiratory quotient

  • RQ = volume of CO evolved ÷ volume of O consumed
  • carbohydrates: RQ = 6CO ÷ 6O = 1.0
  • fats (tripalmitin): RQ = 102CO ÷ 145O = 0.7
  • proteins: RQ about 0.9

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