Class 11 Biology – 14. Breathing and Exchange of Gases

CBSE 2026–27 | NCERT-aligned free study resource

Detailed Chapter Explanation

Human breathing involves ventilation, diffusion across respiratory surfaces, transport of gases and cellular use of oxygen. Diaphragm and intercostal muscles change thoracic volume and pressure. Oxygen is transported mainly through haemoglobin, while carbon dioxide is transported in several forms, especially bicarbonate. Respiratory centres regulate breathing according to chemical conditions.

Core Concepts to Master

Human breathing involves ventilation, diffusion across respiratory surfaces, transport of gases and cellular use of oxygen. Diaphragm and intercostal muscles change thoracic volume and pressure. Oxygen is transported mainly through haemoglobin, while carbon dioxide is transported in several forms, especially bicarbonate. Respiratory centres regulate breathing according to chemical conditions. Students should be able to define the important terms, explain the sequence of major processes, interpret diagrams, compare related concepts and connect structure with function. Answers should use precise NCERT/CBSE terminology rather than generic statements.

Chapter-Specific Questions

1. During exercise, breathing rate increases. Explain how this helps maintain oxygen supply and carbon-dioxide removal.
2. Write a structured explanation of the most important process or classification in this chapter, using correct sequence and terminology.
3. Prepare a comparison table covering at least three meaningful differences between two related concepts from this chapter.
4. Draw and label the most important diagram relevant to this chapter and explain what each major label does.

MCQs

1. Which statement best represents the central idea of this chapter? Answer: Read the detailed explanation above and identify the structure, process or classification specific to this chapter.
2. A CBSE competency question is best answered by: (A) copying a definition only (B) applying the concept to the situation given (C) writing unrelated facts (D) omitting scientific reasoning. Answer: B.
3. When a question asks “justify”, a strong Biology answer should include: (A) a reason supported by the relevant biological principle (B) only a heading (C) an unrelated example (D) a guess. Answer: A.
4. When a diagram is asked, the answer should have: (A) correct structure and labels (B) decoration only (C) no labels (D) unrelated text. Answer: A.
5. Which resource should be used alongside this page for prescribed content? (A) NCERT Biology Class XI and current CBSE curriculum (B) random social-media posts (C) outdated syllabus only (D) none. Answer: A.

HOTS / Competency Practice

1. Apply the chapter concept to a new situation and explain the biological reasoning step-by-step.
2. Predict the effect of disrupting one major structure or process from this chapter and justify the prediction.
3. A student gives a partially correct explanation of this chapter. Identify what scientific relationship or sequence is missing and correct it.

Short-Answer Practice

1. Define and explain three important terms from this chapter.
2. Differentiate between two closely related concepts in three or more points.
3. Explain one important structure/process in 80–120 words.

Long-Answer Practice

Write a well-organised answer explaining the major concepts of this chapter. Use subheadings, scientific terminology, examples and a labelled diagram/flowchart wherever relevant.

Quick Revision

Revise: definitions → classifications/comparisons → structures and labels → processes and sequences → examples → MCQs → HOTS/competency questions.

CBSE Exam Tip

Answer exactly what the command word asks. For “explain”, give the mechanism; for “differentiate”, provide clear paired differences; for “justify”, give evidence/reasoning; for “draw”, label accurately.