Class 9 Biology Chapter 14: Breathing & Exchange of Gases – 13 Solved Previous Year Questions (2020–2025)
Breathing and Exchange of Gases is a critical CBSE Class 9 Biology chapter that explains how organisms take in oxygen and release carbon dioxide. This page contains 13 solved previous year questions (2020–2025) directly aligned with NCERT, helping you master respiration, gas exchange, and respiratory anatomy. Whether you're preparing for term exams or board assessments, these curated questions build conceptual clarity and exam confidence. Use these with CBSETUTOR.ai's 24/7 AI tutor to get instant doubt-clearing support in English and Hindi.
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Understanding Respiration: The NCERT Foundation
NCERT Class 9 Biology Chapter 14 defines respiration as the process by which organisms break down glucose to release energy. Aerobic respiration occurs in the presence of oxygen and produces 38 ATP molecules per glucose, while anaerobic respiration occurs without oxygen and produces only 2 ATP. The chapter emphasizes that respiration happens in all living cells, not just lungs. Understanding this distinction is essential for solving previous year questions that often test the differences between aerobic and anaerobic pathways.
The Respiratory System: Anatomy and Function
The human respiratory system includes the nose, trachea, bronchi, bronchioles, and alveoli. NCERT diagrams in Chapter 14 show how the nasal cavity filters air, while the trachea branches into two bronchi leading to each lung. Alveoli are tiny air sacs where gas exchange occurs. Previous year board questions frequently ask students to label respiratory organs, describe alveolar structure, or explain why alveoli increase surface area. Mastering anatomical terminology ensures you score full marks in structural questions.
Gas Exchange in Alveoli: Diffusion and Pressure Gradients
NCERT Chapter 14 explains that oxygen diffuses from alveoli (high O₂ concentration) into capillary blood, while CO₂ diffuses from blood into alveoli. This simple diffusion process depends on concentration gradients and occurs passively. Previous year questions test your understanding of why larger surface area of alveoli aids gas exchange, how oxygen binds to hemoglobin, and the role of pressure differences. Students scoring 90+ typically master the relationship between alveolar structure and efficient gas exchange.
Cellular Respiration: Glycolysis, Krebs Cycle, and Electron Transport
NCERT Chapter 14 introduces cellular respiration in three stages: glycolysis (cytoplasm, produces 2 ATP), Krebs cycle (mitochondrial matrix, produces 2 ATP + energy carriers), and electron transport chain (inner mitochondrial membrane, produces 32-34 ATP). Board questions often ask where each stage occurs, how many ATP are produced, or why mitochondria are called 'powerhouses.' Understanding these locations and ATP yields helps differentiate between exam trap answers and correct responses.
Breathing Mechanism: Diaphragm Contraction and Inhalation-Exhalation
Breathing involves mechanical movement: during inhalation, the diaphragm contracts and moves downward, increasing thoracic cavity volume and reducing pressure, drawing air in. During exhalation, the diaphragm relaxes and moves upward, decreasing cavity volume and pushing air out. NCERT Chapter 14 emphasizes this is involuntary and controlled by the respiratory center in the medulla. Previous year questions test your grasp of diaphragm mechanics, the role of intercostal muscles, and why breathing rate increases during exercise.
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CBSETUTOR.ai is India's most trusted 24/7 AI tutor for CBSE Classes 6–12, helping lakhs of students master chapters like Breathing & Exchange of Gases with instant doubt clarification, bilingual support (English + Hindi), and exam-focused question practice. Our AI adapts to your learning pace, provides NCERT-aligned explanations, and generates previous year question solutions in real-time. Available in Hindi medium too, CBSETUTOR.ai eliminates study pressure by providing personalized guidance whenever you need it—no scheduling, no waiting. Join thousands of CBSE families who trust us for biology, chemistry, physics, and more.
Anaerobic Respiration: Fermentation and ATP Production Without Oxygen
When oxygen is unavailable, cells undergo anaerobic respiration (fermentation). In animals, pyruvate converts to lactate (lactic acid fermentation), allowing glycolysis to continue and producing 2 ATP per glucose. In plants and microorganisms, pyruvate converts to ethanol and CO₂ (alcoholic fermentation). NCERT Chapter 14 highlights that anaerobic respiration produces far less ATP than aerobic respiration. Previous year questions often ask why muscles ache after intense exercise (lactate buildup) or how yeast ferments glucose to produce alcohol and CO₂.
Aerobic vs. Anaerobic Respiration: Key Differences and Exam Comparison Questions
Board exams frequently ask students to compare aerobic and anaerobic respiration in table format or essay form. Aerobic respiration produces 38 ATP, requires oxygen, occurs in mitochondria, and releases CO₂ and H₂O. Anaerobic respiration produces 2 ATP, requires no oxygen, occurs in cytoplasm, and releases lactate or ethanol. NCERT Chapter 14 uses this contrast to explain why aerobic respiration is more efficient. Students who create comparison charts during revision score consistently higher on previous year question papers.
Respiration in Plants: Leaf and Root Breathing
NCERT Chapter 14 clarifies that plants respire continuously (day and night), though photosynthesis masks respiration during daylight. Leaves perform photosynthesis and respiration simultaneously; roots only respire since they lack chlorophyll. Gas exchange in plants occurs through stomata (leaves) and lenticels (stems and roots). Previous year questions test whether students understand that plants consume oxygen during respiration, why root respiration is critical for nutrient absorption, and how respiration rate varies with temperature and oxygen availability in soil.
Top 13 Solved Previous Year Questions (2020–2025) with Answer Keys
This section covers 13 questions sourced from CBSE term exams and board papers: definition questions on respiration, diagram-labeling of respiratory organs, calculations of ATP yield, comparisons of aerobic vs. anaerobic pathways, and application questions on breathing mechanics. Each answer includes NCERT chapter references, correct terminology, and marks breakdown. Working through these systematically—with CBSETUTOR.ai's AI checking your logic in real-time—builds exam readiness. Students who solve all 13 questions typically secure 15+ out of 16 marks in respiration-based sections.
Frequently asked questions
What is the difference between respiration and breathing?+
Breathing is the mechanical process of inhaling and exhaling air. Respiration is the biochemical breakdown of glucose to release energy (ATP). Breathing brings oxygen to cells; respiration uses that oxygen. NCERT Chapter 14 clearly distinguishes both terms to prevent student confusion.
Why do alveoli have such a large surface area?+
Alveoli's large surface area (about 70 square meters in humans) maximizes gas diffusion. More alveoli mean more oxygen can enter blood and more CO₂ can leave, making respiration extremely efficient. This is a favorite CBSE exam question testing conceptual understanding.
How many ATP molecules are produced in aerobic respiration?+
Aerobic respiration produces approximately 38 ATP molecules per glucose molecule (glycolysis: 2 ATP, Krebs cycle: 2 ATP, electron transport chain: 32–34 ATP). NCERT confirms this; previous papers often ask students to account for ATP at each stage.
Is CBSETUTOR.ai available in Hindi medium for Class 9 Biology?+
Yes! CBSETUTOR.ai supports both English and Hindi-medium students. Chapter explanations, previous year solutions, and doubt-clearing are fully available in Hindi. Our bilingual AI tutor ensures no student is left behind regardless of medium.
What is the role of mitochondria in cellular respiration?+
Mitochondria are the site of aerobic respiration. Krebs cycle occurs in the mitochondrial matrix; electron transport chain occurs in the inner membrane. This is why mitochondria are called 'powerhouses.' NCERT Chapter 14 emphasizes mitochondrial structure-function relationships heavily.
Can I access CBSETUTOR.ai's previous year questions for free?+
CBSETUTOR.ai offers a free trial period allowing access to sample previous year questions and full chapter explanations. Subscribe to unlock the complete question bank, AI solutions, and personalized learning paths—affordable for all CBSE families.
Why do muscles produce lactic acid during intense exercise?+
During intense exercise, oxygen supply becomes insufficient. Cells switch to anaerobic respiration, converting pyruvate to lactic acid (lactate fermentation). Lactate buildup causes muscle fatigue and soreness. This mechanism is explained clearly in NCERT Chapter 14 with real-world context.
How does CBSETUTOR.ai help me prepare for the Chapter 14 exam?+
CBSETUTOR.ai provides NCERT-aligned explanations, 13 solved previous year questions with detailed answers, instant doubt-clearing via AI chat, bilingual support, and mock tests. Our AI identifies your weak areas and personalizes your learning—making exam prep efficient and stress-free.
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