Schooling · Class 11 · Biology · Respiration in Plants · Chapter on a page
CBSE Class 11 · Biology · NCERT Biology
Respiration in Plants: chapter on a page
A cut of Shishya's notes for this chapter: the first paragraph of the introduction and the key ideas, formulas and facts, common mistakes and quick revision lists, word for word. Nothing is added or reworded; the worked examples are left out (they are on the chapter page).
About the notes: Written by Shishya's AI on 27 Sept 2026 from the chapter's title and class level, in Shishya's own words — not a copy or summary of the textbook. Read the official chapter for the book's own text, activities and exercises.
This note's current text has no applied fact-check on record.
Mind map
Drawn from the same notes by a fixed rule (no AI): each label is the item's own words — its bold term, its label before a colon, a short formula as written, or its first words.
The mind map as a list
- Key ideas
- Respiration is an oxidation process
- Glycolysis
- Pyruvate enters the mitochondrion
- The Krebs cycle
- The electron transport chain (ETC)
- Fermentation
- Respiratory quotient (RQ)
- Formulas and facts
- Net ATP from glycolysis
- Overall equation for aerobic…
- Alcoholic fermentation equation
- Lactic acid fermentation equation
- RQ formula
- Sites
- Chemiosmotic hypothesis
- Worked examples
- Calculating RQ for a fat
- ATP yield from Krebs cycle
- Fermentation in dough
- Watch out for
- Thinking respiration happens only…
- Confusing RQ greater than 1 with…
- Believing fermentation produces no ATP
- Assuming all 38 ATP are made per…
- Forgetting that the Krebs cycle…
What this chapter is about
This chapter explains how plants obtain energy from organic compounds through the process of cellular respiration. While photosynthesis captures light energy and stores it in glucose, respiration releases that stored energy in a controlled manner so cells can use it for growth, repair, transport and other life processes. You will learn that respiration is not the same as breathing; it is a biochemical process occurring inside every living cell.
Key ideas
- Respiration is an oxidation process in which organic molecules (mainly glucose) are broken down stepwise; energy released is trapped in ATP bonds rather than lost as heat all at once.
- Glycolysis occurs in the cytoplasm, does not require oxygen, and converts one molecule of glucose (6 carbons) into two molecules of pyruvate (3 carbons each), producing a net gain of 2 ATP and 2 NADH.
- Pyruvate enters the mitochondrion where, under aerobic conditions, it loses CO₂ and combines with coenzyme A to form acetyl-CoA (the link reaction), releasing NADH.
- The Krebs cycle (citric acid cycle) runs in the mitochondrial matrix; acetyl-CoA combines with oxaloacetate to form citrate, and through a cyclic series of reactions, 2 CO₂, 3 NADH, 1 FADH₂ and 1 ATP (or GTP) are produced per acetyl-CoA.
- The electron transport chain (ETC) is located on the inner mitochondrial membrane; electrons from NADH and FADH₂ pass through protein complexes, and the energy released pumps H⁺ ions to create a proton gradient used by ATP synthase to make ATP (oxidative phosphorylation).
- Fermentation is anaerobic respiration in which pyruvate is converted to ethanol and CO₂ (alcoholic fermentation) or to lactic acid (lactic acid fermentation) without passing through the Krebs cycle; it yields only 2 ATP per glucose.
- Respiratory quotient (RQ) = volume of CO₂ released ÷ volume of O₂ consumed. RQ varies: approximately 1 for carbohydrates, less than 1 for fats, greater than 1 for organic acids.
- Amphibolic nature of respiration: the pathways of respiration not only break down substrates (catabolism) but also supply intermediates for biosynthesis of amino acids, fatty acids and other molecules (anabolism).
Formulas and facts to remember
- Net ATP from glycolysis = 2 ATP per glucose (after subtracting 2 ATP used in the preparatory phase).
- Overall equation for aerobic respiration: C₆H₁₂O₆ + 6 O₂ → 6 CO₂ + 6 H₂O + energy (approximately 30–32 ATP in eukaryotes).
- Alcoholic fermentation equation: C₆H₁₂O₆ → 2 C₂H₅OH + 2 CO₂ + 2 ATP.
- Lactic acid fermentation equation: C₆H₁₂O₆ → 2 CH₃CHOHCOOH + 2 ATP.
- RQ formula: RQ = CO₂ evolved / O₂ consumed. For glucose RQ = 6 CO₂ / 6 O₂ = 1.
- Sites: Glycolysis—cytoplasm; Krebs cycle—mitochondrial matrix; ETC and oxidative phosphorylation—inner mitochondrial membrane.
- Chemiosmotic hypothesis (Peter Mitchell): the proton gradient across the inner mitochondrial membrane drives ATP synthesis through ATP synthase.
- Total NADH yield from one glucose (aerobic): 2 (glycolysis) + 2 (link reaction) + 6 (Krebs cycle) = 10 NADH; plus 2 FADH₂ from Krebs cycle.
Common mistakes
- Thinking respiration happens only when a plant is in the dark → respiration occurs continuously, day and night, in all living cells.
- Confusing RQ greater than 1 with inefficient respiration → RQ > 1 simply means the substrate (like organic acids) releases more CO₂ relative to O₂ consumed.
- Believing fermentation produces no ATP → fermentation does produce 2 ATP per glucose through substrate-level phosphorylation in glycolysis.
- Assuming all 38 ATP are made per glucose → in eukaryotes, due to the cost of transporting NADH into mitochondria, the practical yield is about 30–32 ATP.
- Forgetting that the Krebs cycle turns twice per glucose → one glucose gives two acetyl-CoA, so every product of the cycle must be doubled.
Quick revision
- Glycolysis splits glucose (6C) into two pyruvate (3C each), yielding 2 ATP and 2 NADH, and occurs in the cytoplasm without oxygen.
- Krebs cycle runs in the mitochondrial matrix and produces NADH, FADH₂, ATP and CO₂ from acetyl-CoA.
- The ETC uses electrons from NADH and FADH₂ to build a proton gradient; ATP synthase then makes most of the cell's ATP.
- Fermentation regenerates NAD⁺ so glycolysis can continue when oxygen is absent; net gain is only 2 ATP.
- RQ = 1 for carbohydrates, < 1 for fats, > 1 for organic acids.
- Respiration is amphibolic—its intermediates serve both energy release and biosynthesis.