Class 11 Biology Chapter 14 Breathing and Exchange of Gases – Revision Notes

Air moves through a defined pathway from nostrils to alveoli in this chapter, which also details how oxygen and carbon dioxide are transported and how the medulla regulates breathing rate.

Last Updated: September 23, 2026

Respiratory Pathway

• Nostrils → pharynx → larynx → trachea → bronchi → bronchioles → alveoli.

Breathing Mechanism

• Inspiration: diaphragm contracts, thoracic volume up, pressure down.
• Expiration: diaphragm relaxes, volume down, pressure up.

Gas Transport

• O₂: ~97% via haemoglobin (oxyhaemoglobin).
• CO₂: ~70% as bicarbonate, ~20-25% carbaminohaemoglobin.

Regulation

• Respiratory rhythm centre (medulla oblongata); primarily CO₂-sensitive.

One-Line Summary

Breathing moves air through the respiratory tract to the alveoli, where O₂ and CO₂ are exchanged by diffusion and transported in blood, with breathing rate regulated mainly by blood CO₂ levels via the medulla oblongata.

Frequently Asked Questions

What is the difference between breathing and respiration as clarified in this chapter?
Breathing is the physical process of inhaling and exhaling air to exchange oxygen and carbon dioxide with the environment, while respiration is the biochemical process inside cells that uses oxygen to break down food and release energy.

How does the structure of alveoli make them efficient for gas exchange?
Alveoli have extremely thin walls and are surrounded by a dense network of capillaries, providing a large surface area and a short diffusion distance, which together make gas exchange highly efficient.

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.