NCERT Solution for Class 11 Biology Chapter 17 BREATHING AND EXCHANGE OF GASES

Welcome to Swastik Classes! In this comprehensive NCERT Solution series, we present to you the detailed solutions for Class 11 Biology Chapter 17: “Breathing and Exchange of Gases.” This chapter delves into the fascinating world of respiratory systems and the exchange of gases in living organisms.

In this chapter, we explore the essential processes involved in breathing and the mechanisms by which organisms acquire oxygen and remove carbon dioxide from their bodies. From the structure and functioning of respiratory organs to the role of various gases in the process, we cover it all. Our meticulously crafted solutions aim to provide you with a deep understanding of this fundamental biological process.

Our team of experienced educators has meticulously analyzed and broken down each concept, ensuring clarity and simplicity in explanations. These solutions are designed to help you grasp the intricate details of the respiratory system, ensuring that you can confidently tackle any question related to this topic.

We understand that mastering biology requires more than just rote learning. Therefore, our solutions include insightful explanations, diagrams, and examples, enabling you to connect theoretical knowledge with real-life applications. By using our NCERT solutions, you will not only enhance your conceptual understanding but also develop problem-solving skills to excel in examinations.

At Swastik Classes, we are committed to providing you with the best educational resources. Our NCERT Solution series for Class 11 Biology Chapter 17: “Breathing and Exchange of Gases” is a valuable tool to help you navigate through the complexities of this chapter. We believe that a solid foundation in biology will equip you to explore and understand the wonders of life.

So, embark on this learning journey with us and let’s unravel the mysteries of breathing and the exchange of gases together!

NCERT Solution for Class 11 Biology Chapter 17 BREATHING AND EXCHANGE OF GASES – Exercises

1. Define vital capacity. What is its significance?

Sol. Vital capacity is defined as the maximum volume of air a person can breathe in after a forced expiration or the maximum volume of air a person can breathe out after a forced inspiration. It represents the maximum amount of air one can renew in the respiratory system in a single respiration. Thus, greater the vital capacity more is the energy available to the body.

2. State the volume of air remaining in the lungs after a normal breathing.

Sol. When a person breathes normally, the amount which remains in the lung after normal expiration, is called functional residual capacity. It is the sum of residual volume and the expiratory reserve volume (FRC = RV + ERV). It is about 2100 – 2300 mL of air.

3. Diffusion of gases occurs in the alveolar region only and not in the other parts of respiratory system. Why?

Sol. For efficient exchange of gases, respi: atory surface must have certain characteristics such as (i) it must be thin, me ist and permeable to respiratory gases (ii) it must have large surface area, (iii) it must be highly vascular. Only alveolar region has these characteristics. Thus, diffusion of gases occurs in this region only.

4. What are the major transport mechanisms for CO2? Explain.

Sol. Nearly 20-25 percent of CO2 is transported by haemoglobin of RBCs, 70 percent of it is carried as bicarbonate ion in

plasma and about 7 percent of CO2 is carried in a dissolved state through plasma. CO2 is carried by haemoglobin as carbamino- haemoglobin. This binding is related to the partial pressure of CO2.

5. What will be the p02 and pCO2 in the atmospheric air compared to those in the alveolar air?

(i) pO2 lesser, pCO2 higher

(ii) pO2 higher, pCO2 lesser

(iii) pO2 higher, pCO2 higher

(iv) pO2 lesser, pCO2 lesser

Sol. (ii) Air that has entered the alveoli through the bronchioles is called alveolar air. It has the same partial pressure of CO2 and 02 as is in the atmospheric air. Then, there occurs gaseous exchange between the adjacent blood capillaries and the alveoli. CO2 diffuses from blood into the alveolar air and O2 diffuses from alveolar air to the blood. As a result, new alveolar air has higher pCO2and lesser pO2, than the atmospheric air.

6. Explain the process of inspiration under normal conditions.

Sol. Inspiration is a process by which fresh air enters the lungs. The diaphragm, intercostal muscles and abdominal muscles play an important role. The muscles of the diaphragm and external intercostal muscles are principle muscles of inspiration. Volume of thoracic cavity increases by contraction of diaphragm and external intercostal muscles. During inspiration, relaxation of abdominal muscles also occurs which allows compression of the abdominal organs by diaphragm. Thus, overall volume of the thoracic cavity increases and as a result, there is a decrease of the air pressure in the lungs. The greater pressure outside the body now causes air to flow rapidly into the lungs. The sequence of air flow is.

7. How is respiration regulated?

Sol. Respiration is under both nervous and chemical regulation.

The respiratory centre in brain is composed of groups of neurons located in the medulla oblongata and pons varolii. The respiratory centre regulates the rate and depth of the breathing.

Dorsal respiratory group of neurons are located in the dorsal portion of the medulla oblongata. This group of neurons mainly causes inspiration.

Ventral group of neurons are located in the ventrolateral part of the medulla oblongata. These can cause either inspiration or expiration.

Pneumotaxic centre is located in the dorsal part of pons varolii. It sends signals to all the neurons of dorsal respiratory group and only to inspiratory neurons of ventral respiratory group. Its job is primarily to limit inspiration. Chemically, respiration is regulated by the large numbers of chemoreceptors located in the carotid bodies and in the aortic bodies. Excess carbon dioxide or hydrogen ions mainly stimulate the respiratory centre of the brain and increases the inspiratory and expiratory-signals to the respiratory muscles. Increased C02 lowers the pH resulting in acidosis. The role of oxygen in the regulation of respiratory rhythm is quite insignificant.

8. What is the effect of pCO2on oxygen transport?

Sol. Increase in pCO2 tension in blood brings rightward shift of the oxygen dissociation curve of haemoglobin thereby decreasing the affinity of haemoglobin for oxygen. This effect is called Bohr’s effect. It plays an important role in the release of oxygen in the tissues.

9. What happens to the respiratory process in a man going up a hill?

Sol. Rate of breathing will increase in order to supply sufficient oxygen to blood because air in mountainous region is deficient in oxygen.

10. What is the site of gaseous exchange in an insect?

Sol. Tracheae (Tracheal respiration) is the site of gaseous exchange in an insect. .

11. Define oxygen dissociation curve. Can you suggest any reason for its sigmoidal pattern?

Sol. The relationship between the partial pressure of oxygen (pO2) and percentage saturation of the haemoglobin with oxygen (O2)is graphically illustrated by a curve called oxygen haemoglobin dissociation curve (also called oxygen dissociation curve).

The sigmoidal pattern of oxygen haemoglobin dissociation curve is the result of two properties which play significant role in the transport of oxygen. These two properties are:

(i) Minimal loss of oxygen from haemoglobin occurs above p02 of 70-80 mm Hg despite significant changes in tension of oxygen beyond this. This is depicted by relatively flat portion of the curve.

(ii)Any further decline in p02 from 40 mm Hg causes a disproportionately greater release of oxygen from the haemoglobin. It results in the steeper portion of the curve and causes the curve to be sigmoid.

12. Have you heard about hypoxia? Try to gather information about it, and discuss with your friends.

Sol. Hypoxia is a condition of oxygen shortage in the tissues. It is of two types:

(i) Artificial hypoxia: It results from shortage of oxygen in the air as at high altitude. It causes mountain sickness characterised by breathelessnes, headache, dizziness and bluish tinge on skin.

(ii) Anaemic hypoxia: It results from the reduced oxygen carrying capacity of the blood due to anaemia or carbon monoxide poisoning. In both cases, less haemoglobin is available for carrying 02.

13. Distinguish between

(a) IRV and ERV

(b) Inspiratory capacity and expiratory capacity.

(c) Vital capacity and total lung capacity.


(a) Differences between IRV and ERV are as follows:


(b)Differences between inspiratory capacity and expiratory capacity are as follows:


(c) Differences between vital capacity and total lung capacity are as follows:


14. What is tidal volume? Find out the tidal volume (approximate value) for a healthy human in an hour.

Sol. Tidal volume is the volume of air inspired or expired with each normal breath. This is about 500 mL in an adult person. It is composed of about 350 mL of alveolar volume and about 150 mL of dead space volume. The alveolar volume consists of air that reaches the respiratory surfaces of the alveoli and engages in gas exchange. The dead space volume consists of air that does not reach the respiratory surfaces.

A healthy man can inspire or expire approximately 6000 to 8000 mL of air per minute. Therefore, tidal volume for a healthy human in an hour is 360 – 480 mL of air.

Conclusions for NCERT Solution for Class 11 Biology Chapter 17 BREATHING AND EXCHANGE OF GASES

the NCERT Solution series for Class 11 Biology Chapter 17: “Breathing and Exchange of Gases” by Swastik Classes provides a comprehensive and insightful understanding of the respiratory system and the exchange of gases in living organisms.

Throughout this chapter, we have explored the intricacies of breathing, the structure and functioning of respiratory organs, and the crucial role of various gases involved in the process. Our meticulously crafted solutions have aimed to simplify complex concepts, making it easier for students to grasp and apply their knowledge.

By using our NCERT solutions, students have had the opportunity to deepen their conceptual understanding and develop problem-solving skills. The detailed explanations, diagrams, and examples provided in our solutions have allowed students to connect theoretical knowledge with real-life applications, fostering a holistic approach to learning.

At Swastik Classes, we strive to provide the best educational resources, and our NCERT Solution series for Class 11 Biology Chapter 17: “Breathing and Exchange of Gases” is no exception. We believe that a strong foundation in biology is essential for students to appreciate the wonders of life and excel academically.

We hope that our solutions have equipped students with the necessary tools to confidently tackle any question related to this chapter. By mastering the concepts covered in this chapter, students will be well-prepared to explore further topics in biology and pursue their academic goals.

Thank you for choosing Swastik Classes as your trusted learning companion. We wish you success in your biology studies and encourage you to continue exploring the fascinating world of science!

  1. Q: What is the role of hemoglobin in the respiratory system? A: Hemoglobin is a protein found in red blood cells that plays a crucial role in the respiratory system. It binds to oxygen in the lungs, forming oxyhemoglobin, and carries it to the body tissues. In the tissues, hemoglobin releases oxygen and picks up carbon dioxide, forming carbaminohemoglobin. This oxygen-carbon dioxide exchange enables efficient transport of gases in the body.
  2. Q: What are the differences between breathing and respiration? A: Breathing and respiration are often used interchangeably, but they have distinct meanings. Breathing refers to the physical process of inhaling and exhaling, where air moves in and out of the respiratory system. Respiration, on the other hand, is the cellular process that involves the breakdown of glucose to release energy and produce carbon dioxide as a byproduct.
  3. Q: What is the significance of the respiratory pigment in different organisms? A: Respiratory pigments, such as hemoglobin in humans and myoglobin in muscles, have high affinity for oxygen and enhance the oxygen-carrying capacity of blood and tissues. These pigments allow organisms to extract more oxygen from the environment and transport it to body cells efficiently. The presence of respiratory pigments enables organisms to adapt to diverse environmental conditions and perform aerobic respiration effectively.
  4. Q: How does the human respiratory system protect itself from harmful substances? A: The human respiratory system has various protective mechanisms to safeguard itself from harmful substances. The nasal passages are lined with tiny hair-like structures called cilia that trap dust particles and prevent them from entering the lungs. The mucus produced by the respiratory tract also acts as a sticky barrier to trap foreign particles. Additionally, coughing and sneezing reflexes expel irritants, and the presence of antibodies and immune cells in the respiratory system helps in neutralizing harmful substances.
  5. Q: What is the role of surfactant in the lungs? A: Surfactant is a substance produced by specialized cells in the lungs called type II alveolar cells. It reduces the surface tension of the fluid lining the alveoli (air sacs) and prevents their collapse during exhalation. Surfactant also helps in the efficient exchange of gases by keeping the alveoli open, allowing oxygen to enter and carbon dioxide to be expelled easily.
swc google search e1651044504923