Class 11 Biology Chapter 12 Respiration in Plants – Revision Notes

Respiration in plants is traced through glycolysis in the cytoplasm to the Krebs cycle and electron transport in the mitochondria, contrasted with the incomplete energy yield of fermentation.

Last Updated: September 23, 2026

Glycolysis

• Cytoplasm; glucose → 2 pyruvate; net 2 ATP, 2 NADH.

Fermentation

• Alcoholic (yeast: ethanol+CO₂) or lactic acid; net 2 ATP; incomplete oxidation.

Aerobic Respiration

• Krebs cycle (mitochondrial matrix): Acetyl CoA → CO₂+NADH+FADH₂+ATP.
• ETS (inner mitochondrial membrane): oxidative phosphorylation, O₂ final acceptor, ~36-38 ATP total.

RQ

• RQ=CO₂ evolved/O₂ consumed; =1 (carbs), <1 (fats/proteins), >1 (organic acids).

One-Line Summary

Cellular respiration breaks down glucose via glycolysis, and either fermentation (anaerobic, low ATP yield) or the Krebs cycle plus electron transport chain (aerobic, high ATP yield via oxidative phosphorylation with oxygen as final electron acceptor).

Frequently Asked Questions

What is the difference between aerobic and anaerobic respiration in plants?
Aerobic respiration uses oxygen to completely break down glucose into carbon dioxide and water, releasing a large amount of energy, while anaerobic respiration occurs without oxygen and breaks down glucose only partially, releasing much less energy.

Why is respiration described as a catabolic and exergonic process?
Respiration is catabolic because it breaks down complex organic molecules like glucose into simpler ones, and it is exergonic because this breakdown releases energy that the plant cell captures and stores as ATP.

Written by Satish

NCERTBooks.org is an independent educational resource run by a small team focused on making official NCERT textbooks easy to find, read, and download for students, parents, and teachers across India. We are not affiliated with NCERT or the Ministry of Education -- we organise publicly available NCERT content by class and subject, verify links against official sources, and build tools (like our in-browser reader) that make studying more convenient. Every guide we publish is written and reviewed by our team based on the actual NCERT curriculum and syllabus.