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CBSE Class 11 Biology Chapter 14 Breathing & Exchange of Gases Worksheet with Answers

Chapter 14 Breathing & Exchange of Gases is fundamental to understanding human physiology in CBSE Class 11 Biology. This worksheet systematically tests your grasp of respiratory organs, breathing mechanisms, and gas transport as outlined in NCERT Class 11 Biology. With difficulty graded from basic recall to HOTS application questions, it prepares you for board exams while reinforcing core concepts through varied question formats.

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Key takeaways

✓Worksheet covers all three major NCERT topics: respiratory organs, mechanism of breathing, and transport of gases with varying difficulty levels
✓6 multiple-choice questions test conceptual understanding of alveolar exchange and respiratory volumes
✓5 short-answer questions focus on processes like Bohr effect, carbonic anhydrase role, and partial pressure gradients
✓3 HOTS long-answer questions require application of breathing mechanics, oxygen-haemoglobin dissociation, and comparative respiratory anatomy
✓Complete answer key with explanations helps students self-assess and understand common errors in gas exchange concepts
✓Suggested time limit of 90 minutes mirrors CBSE exam conditions for effective practice
✓Case-study question integrates real-life scenarios like high-altitude adaptation and respiratory disorders

Worksheet Overview and Instructions

This printable worksheet is designed for CBSE Class 11 students preparing for Biology board exams and unit tests. The difficulty level is moderate to challenging, matching the 2025 CBSE Class 11 Biology syllabus standards. Students should allocate 90 minutes to complete all sections under exam-like conditions for maximum benefit. The worksheet covers respiratory organs in detail, mechanism of breathing including inspiration and expiration, exchange of gases at alveolar and tissue levels, and transport of oxygen and carbon dioxide in blood. Each section progressively builds complexity, starting with objective questions and culminating in case-based analysis. Use blue or black pen for answers and attempt all questions before consulting the answer key. This practice helps identify weak areas in Class 11 Biology Chapter 14 that need focused revision using NCERT Class 11 Biology textbook and solutions.

Difficulty level: Moderate to challenging
Suggested time: 90 minutes
Total marks: 50
Required materials: NCERT Class 11 Biology textbook, pen, pencil for diagrams

Quick Chapter Recap: Breathing & Exchange of Gases

Chapter 14 Breathing & Exchange of Gases in NCERT Class 11 Biology explains how organisms obtain oxygen and eliminate carbon dioxide. Humans use a pair of lungs located in the thoracic cavity for this purpose. The chapter details the anatomy of the respiratory system including the conducting portion like nostrils, pharynx, larynx, trachea, bronchi, and bronchioles, and the respiratory portion comprising alveoli where actual gas exchange occurs. The mechanism of breathing involves inspiration driven by diaphragm contraction and external intercostal muscle action, and expiration which is largely passive at rest. Respiratory volumes and capacities such as tidal volume approximately 500 mL, inspiratory reserve volume about 2500-3000 mL, and vital capacity around 3500-4500 mL are clinically significant. Gases move by diffusion following partial pressure gradients: oxygen partial pressure in alveoli is about 104 mm Hg versus 40 mm Hg in deoxygenated blood. Oxygen transport occurs primarily bound to haemoglobin forming oxyhaemoglobin, while carbon dioxide is carried as bicarbonate ions approximately seventy percent, carbamino-haemoglobin about twenty-three percent, and dissolved in plasma around seven percent.

Respiratory organs: Nostrils, pharynx, larynx, trachea, bronchi, bronchioles, and alveoli
Inspiration: Active process involving diaphragm and external intercostal muscles
Expiration: Passive process at rest; becomes active during exercise
Oxygen transport: 97% as oxyhaemoglobin, 3% dissolved in plasma
CO₂ transport: 70% as bicarbonate, 23% as carbamino-haemoglobin, 7% dissolved

Section A: Multiple Choice Questions (1 mark each)

Multiple-choice questions test your conceptual clarity on CBSE Class 11 Biology Chapter 14 topics. Each question has four options with only one correct answer. These MCQs cover respiratory anatomy, breathing mechanics, partial pressures, oxygen-haemoglobin dissociation curve, and carbon dioxide transport mechanisms as per NCERT Class 11 Biology curriculum. Focus on understanding why an option is correct rather than memorizing answers. Common areas tested include the role of carbonic anhydrase enzyme found in high concentration in red blood cells, factors affecting haemoglobin oxygen affinity such as pH, temperature, and carbon dioxide concentration, and distinguishing between vital capacity and total lung capacity. Students often confuse inspiratory capacity with inspiratory reserve volume, so read questions carefully. These Class 11 Biology solutions require precise knowledge of numerical values like partial pressures at different body sites and percentage contributions of different carbon dioxide transport forms mentioned in NCERT textbooks.

Q1. The respiratory centre in the brain is primarily located in which region?
Q2. What is the partial pressure of oxygen in alveolar air?
Q3. Carbonic anhydrase enzyme is present in high concentration in which cells?
Q4. Which respiratory volume cannot be measured by spirometry?
Q5. The oxygen-haemoglobin dissociation curve shifts to the right due to which condition?
Q6. Approximately what percentage of carbon dioxide is transported as bicarbonate ions?

Section B: Fill in the Blanks (1 mark each)

Fill-in-the-blank questions assess your recall of specific terms, numerical values, and functional relationships in Chapter 14 Breathing & Exchange of Gases. These questions require exact terminology used in NCERT Class 11 Biology textbook. Pay special attention to scientific names, enzyme names like carbonic anhydrase, specific anatomical structures such as the epiglottis or pleural membrane, and numerical values for respiratory volumes. Students preparing for CBSE 11 Biology exams should note that spellings matter in board examinations, so practice writing terms correctly. Common blanks test knowledge of tidal volume default value around 500 millilitres, the number of lobes in right lung which is three, the cartilaginous structure called the Adam's apple or larynx, and the thin squamous epithelium lining alveoli for efficient gas diffusion. Review Class 11 Biology notes focusing on bold and italicized terms in your NCERT textbook before attempting this section for optimal performance.

Q1. The volume of air inspired or expired during normal breathing is called _________.
Q2. The enzyme _________ catalyses the formation of carbonic acid from carbon dioxide and water.
Q3. The partition separating the thoracic cavity from the abdominal cavity is called _________.
Q4. Human lungs are covered by a double-layered membrane called _________.
Q5. The condition in which carbon dioxide accumulates in blood is termed _________.

Section C: True or False Statements (1 mark each)

True or false questions challenge your ability to distinguish accurate statements from common misconceptions in CBSE Class 11 Biology Chapter 14. Each statement relates directly to NCERT Class 11 Biology content on breathing mechanisms, gas exchange, or transport. Some statements are deliberately tricky, testing subtle differences such as 'expiration is always a passive process' which is false because during vigorous exercise expiration becomes active involving internal intercostal muscles and abdominal muscles. Students often mark incorrectly on statements about haemoglobin saturation, partial pressure values, and the direction of gas diffusion. When a statement is false, you should be able to correct it mentally, demonstrating deep understanding. For instance, if asked whether oxygen is mainly transported dissolved in plasma, you should know this is false as ninety-seven percent binds to haemoglobin. These Class 11 Biology solutions require careful reading of qualifiers like 'always,' 'never,' 'only,' and 'primarily' which often indicate false statements when used incorrectly in the context of respiratory physiology covered in your textbook.

Q1. Expiration is always a passive process in humans.
Q2. The partial pressure of oxygen is higher in alveoli than in deoxygenated blood.
Q3. Carbonic anhydrase is present in blood plasma.
Q4. Vital capacity includes residual volume.
Q5. Haemoglobin has a lower affinity for oxygen at higher pH levels.
Q6. The left lung has three lobes while the right lung has two lobes.
Q7. Cigarette smoking reduces the surface area available for gas exchange.
Q8. The respiratory rhythm is primarily controlled by the cerebellum.
Q9. Oxygen dissociation from haemoglobin is facilitated in metabolically active tissues.
Q10. Pneumotaxic centre is located in the pons region of the brain.

Section D: Short Answer Questions (2 marks each)

Short-answer questions in this CBSE Class 11 Biology worksheet require concise explanations of key concepts from Chapter 14 Breathing & Exchange of Gases. Each answer should be 30-50 words, directly addressing the question using NCERT Class 11 Biology terminology. Focus on clear definitions, two or three key points, and avoiding unnecessary elaboration. These questions test your understanding of physiological processes like the Bohr effect, role of specific enzymes, significance of respiratory volumes, and mechanisms of gas diffusion. When explaining the role of carbonic anhydrase, mention both forward reaction in tissues forming carbonic acid and reverse reaction in lungs releasing carbon dioxide. For questions on partial pressure gradients, always specify numerical values from your Class 11 Biology notes to demonstrate precision. Students often lose marks by giving vague answers without specific examples or values. Reference NCERT diagrams mentally while answering questions about alveolar structure or the oxygen-haemoglobin dissociation curve to ensure completeness in your Class 11 Biology solutions.

Q1. Explain the Bohr effect and its physiological significance.
Q2. What is the role of carbonic anhydrase in respiration?
Q3. Differentiate between inspiratory capacity and vital capacity.
Q4. How does partial pressure gradient facilitate oxygen diffusion in alveoli?
Q5. Why is residual volume important even though it cannot be expired?

Section E: Long Answer and HOTS Questions (5 marks each)

Long-answer questions require comprehensive responses of 100-150 words demonstrating deep understanding of CBSE Class 11 Biology Chapter 14 concepts. These HOTS or Higher Order Thinking Skills questions go beyond recall, asking you to explain mechanisms, draw comparisons, analyze situations, or integrate multiple concepts. Structure your answer with a brief introduction, three to four main points with explanations, and a concluding statement. When describing the mechanism of breathing, detail both inspiration and expiration, role of diaphragm and intercostal muscles, pressure changes in thoracic cavity, and how Boyle's law applies. For the oxygen-haemoglobin dissociation curve question, draw a neat S-shaped curve, label axes with partial pressure of oxygen in mm Hg and percentage saturation, mark key points like P50 around 26-27 mm Hg, and explain factors shifting the curve right like increased temperature, CO₂, or decreased pH. Include relevant numerical values from NCERT Class 11 Biology to strengthen answers. These Class 11 Biology solutions should reflect textbook explanations while demonstrating your ability to articulate complex physiological processes clearly for board exam success.

Q1. Describe the mechanism of breathing in humans, explaining both inspiration and expiration.
Q2. Explain the oxygen-haemoglobin dissociation curve and factors affecting it. Draw a labeled diagram.
Q3. Compare and contrast the transport of oxygen and carbon dioxide in blood.

Section F: Case Study Question (4 marks)

Case-study questions have become increasingly important in CBSE Class 11 Biology examinations since 2023. These questions present a real-life scenario or experimental observation related to Chapter 14 Breathing & Exchange of Gases, followed by 3-4 sub-questions testing your ability to apply theoretical knowledge from NCERT Class 11 Biology to practical situations. Read the case passage carefully, identify key information such as numerical data, symptoms described, or experimental conditions, and then answer each sub-question precisely. Common case studies involve high-altitude adaptation where reduced atmospheric pressure affects oxygen availability, respiratory disorders like emphysema reducing alveolar surface area, or physiological responses during exercise when oxygen demand increases. Your Class 11 Biology notes should include such applications. When answering, always link back to the case details provided rather than giving generic textbook answers. For instance, if the case mentions a trekker at 4000 meters altitude experiencing breathlessness, explain this using partial pressure of oxygen decrease at high altitude affecting the diffusion gradient, not just general breathing mechanism. These questions develop analytical skills essential for medical entrance exams like NEET where CBSE 11 Biology forms the foundation.

Read the case passage describing a mountaineer experiencing breathlessness at 3500 meters altitude
Sub-question (a): Explain why oxygen saturation of haemoglobin decreases at high altitude (1 mark)
Sub-question (b): What compensatory mechanisms does the body employ during acclimatization? (2 marks)
Sub-question (c): How does hyperventilation help in this situation? (1 mark)

Complete Answer Key with Explanations

This comprehensive answer key provides correct answers and brief explanations for all questions in the CBSE Class 11 Biology Chapter 14 worksheet. Each explanation references NCERT Class 11 Biology content to help you understand not just what the answer is but why it is correct. For multiple-choice questions, explanations clarify why other options are incorrect, addressing common misconceptions. Fill-in-the-blank answers include acceptable alternate phrasings where applicable, though CBSE marking schemes prefer exact NCERT terminology. True/false explanations correct false statements, turning them into learning opportunities. Short-answer model responses demonstrate the appropriate depth and format expected in board exams, typically two to three sentences with key terminology. Long-answer explanations outline the structure and main points without providing full essays, encouraging you to develop complete responses independently. For the case-study question, answers show how to extract information from the passage and apply Chapter 14 concepts. Use this answer key for self-assessment after attempting all questions honestly. If you score below seventy percent, revisit relevant NCERT sections and Class 11 Biology notes before attempting additional practice questions. For personalized doubt-clearing and step-by-step solutions with photo upload, consider CBSETUTOR.ai offering 24x7 AI tutoring at flat ₹999 monthly for all classes 6-12 with a 3-day free trial.

Section A Answer Key: Multiple Choice Questions

Here are the correct answers with explanations for all six MCQs in Section A of this Class 11 Biology Chapter 14 worksheet. Question 1: The respiratory centre is primarily located in option (c) medulla oblongata of the brain stem, which contains dorsal and ventral respiratory groups of neurons regulating rhythmic breathing. The cerebrum controls voluntary breathing modifications. Question 2: The partial pressure of oxygen in alveolar air is approximately option (b) 104 mm Hg, as mentioned in NCERT Class 11 Biology, creating a gradient for diffusion into blood at 40 mm Hg. Question 3: Carbonic anhydrase enzyme is present in high concentration in option (c) red blood cells or erythrocytes, not in plasma, catalyzing rapid interconversion of CO₂ and H₂CO₃. Question 4: Option (d) residual volume cannot be measured by spirometry because it is the air remaining in lungs after maximum expiration, requiring special techniques like helium dilution method. Question 5: The oxygen-haemoglobin dissociation curve shifts to the right due to option (b) increased carbon dioxide concentration, also increased temperature or decreased pH, reflecting the Bohr effect that reduces oxygen affinity. Question 6: Approximately option (c) seventy percent of carbon dioxide is transported as bicarbonate ions in plasma, formed by the action of carbonic anhydrase in RBCs.

Q1: (c) Medulla oblongata - houses dorsal and ventral respiratory groups
Q2: (b) 104 mm Hg - alveolar oxygen partial pressure enabling diffusion
Q3: (c) Red blood cells - high carbonic anhydrase concentration
Q4: (d) Residual volume - remains after maximum expiration, unmeasurable by spirometry
Q5: (b) Increased CO₂ concentration - demonstrates Bohr effect
Q6: (c) 70% - bicarbonate ions primary CO₂ transport mechanism

Section B, C, D, E and F Answer Key

Section B Fill in the Blanks Answers: (1) tidal volume, (2) carbonic anhydrase, (3) diaphragm, (4) pleura or pleural membrane, (5) hypercapnia. Section C True or False Answers: (1) False - expiration is passive during quiet breathing but active during exercise, (2) True - PO₂ in alveoli is 104 mm Hg versus 40 mm Hg in deoxygenated blood, (3) False - carbonic anhydrase is in RBCs not plasma, (4) False - vital capacity excludes residual volume, (5) False - haemoglobin has higher affinity at higher pH, (6) False - left lung has two lobes and right has three, (7) True - smoking damages alveoli reducing surface area, (8) False - medulla oblongata controls rhythm not cerebellum, (9) True - lower pH and higher CO₂ in active tissues promote oxygen release, (10) True - pneumotaxic centre in pons regulates breathing rate. Section D Short Answers: Q1 Bohr effect is reduced oxygen affinity of haemoglobin at lower pH or higher CO₂, ensuring oxygen release in active tissues. Q2 Carbonic anhydrase catalyzes CO₂ + H₂O ↔ H₂CO₃ reaction, accelerating bicarbonate formation in tissues and CO₂ release in lungs. Q3 Inspiratory capacity is tidal volume plus inspiratory reserve volume around 3000-3500 mL, while vital capacity is inspiratory reserve plus tidal plus expiratory reserve volume around 3500-4500 mL. Q4 Oxygen partial pressure gradient between alveoli at 104 mm Hg and blood at 40 mm Hg drives diffusion across the respiratory membrane until equilibrium. Q5 Residual volume around 1100-1200 mL prevents alveolar collapse, maintains continuous gas exchange between breaths, and keeps lungs inflated. Section E and F require student-developed comprehensive answers based on outlines provided in the worksheet.

Section B focuses on key terminology: tidal volume, carbonic anhydrase, diaphragm, pleura, hypercapnia
Section C tests conceptual accuracy with 10 statements covering breathing mechanics, gas transport, anatomy
Section D model answers demonstrate concise 30-50 word responses with specific values
Section E requires integration of multiple concepts in 100-150 word structured responses
Section F case study tests application of high-altitude physiology to real scenario

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Frequently asked questions

What is the difficulty level of this CBSE Class 11 Biology Chapter 14 worksheet?+

This worksheet has moderate to challenging difficulty, aligned with 2025 CBSE Class 11 Biology board exam standards. It includes basic recall MCQs, application-based short answers, and HOTS questions requiring integration of multiple concepts from Breathing & Exchange of Gases chapter.

How much time should I allocate to complete this worksheet?+

Allocate 90 minutes to complete all sections under exam-like conditions. This includes 10 minutes for Section A MCQs, 8 minutes for Section B, 10 minutes for Section C, 20 minutes for Section D, 30 minutes for Section E, 12 minutes for the case study, leaving time for review.

Are the answers provided in this worksheet aligned with NCERT Class 11 Biology content?+

Yes, all answers and explanations use terminology, numerical values, and concepts directly from NCERT Class 11 Biology Chapter 14. The answer key references specific textbook sections to help you verify and deepen understanding of Breathing & Exchange of Gases topics.

Which topics from Chapter 14 Breathing & Exchange of Gases carry maximum weightage in CBSE exams?+

Mechanism of breathing including the role of diaphragm and intercostal muscles, transport of gases especially the role of carbonic anhydrase and haemoglobin, oxygen-haemoglobin dissociation curve, and respiratory volumes typically carry 3-5 marks each in CBSE Class 11 Biology board exams.

How should I use the answer key effectively for self-study?+

Attempt all questions honestly without looking at answers first. After completion, check your responses against the answer key, reading explanations for both correct and incorrect answers. Note down concepts you missed, then revise those specific sections in your NCERT Class 11 Biology textbook before re-attempting similar questions.

What are common mistakes students make in Chapter 14 Breathing & Exchange of Gases questions?+

Common errors include confusing inspiratory capacity with inspiratory reserve volume, stating incorrect percentage values for CO₂ transport mechanisms, mixing up left and right lung lobe numbers, incorrectly describing expiration as always passive, and forgetting that carbonic anhydrase is in RBCs not plasma.

Is this worksheet sufficient for CBSE Class 11 Biology board exam preparation?+

This worksheet provides excellent practice for Chapter 14, but comprehensive board preparation requires solving NCERT back exercises, previous year question papers, sample papers, and additional worksheets covering all chapters. Use this as one component of a broader Class 11 Biology study plan.

How can I improve my answers to long-answer questions in Section E?+

Structure long answers with an introduction, 3-4 main points with sub-explanations, and a conclusion. Use headings or bullet points for clarity. Include labeled diagrams where asked, specific numerical values from NCERT, and technical terms correctly. Practice writing 100-150 word answers within 6-8 minutes for board exam readiness.

What is the importance of case-study questions in CBSE Class 11 Biology?+

Case-study questions introduced recently in CBSE exams test your ability to apply theoretical knowledge to real-life scenarios. They develop analytical skills essential for medical entrance exams like NEET. For Chapter 14, expect cases on high-altitude adaptation, respiratory disorders, or exercise physiology requiring integration of multiple concepts.

Can I use this worksheet for quick revision before exams?+

Yes, attempting this worksheet one week before exams helps identify weak areas needing focused revision. The MCQs and fill-in-the-blanks test recall of key facts, while short and long answers ensure you can explain mechanisms. The answer key serves as condensed Class 11 Biology notes for last-minute revision of Chapter 14.

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