NCERT Solutions Class 11 Biology Chapter 17
NCERT Solutions for Class 11 Biology Chapter 17
Most CBSE students find it difficult to answer the questions in the chapter Breathing and Exchange of Gases because of the complexity of various concepts it covers. Students will be able to write better answers by referring to the NCERT Solutions for Class 11 Biology Chapter 17. The solutions are explained in simple language which makes it easy to understand. Students can use the NCERT Solutions for Class 11 Chapter 17 by Extramarks as a guide to improve their answer writing skills and have a deeper understanding of the concepts.
NCERT Solutions for Class 11 Biology Chapter 17 – Breathing and Exchange of Gases
The NCERT Solutions for Class 11 Biology Chapter 17 – Breathing and Exchange of gases are easy to understand and learn. The study materials act as a guide that students can refer to while answering the questions given at the end of Chapter 17 in the NCERT textbook.
Access NCERT Solutions for Class 11 Biology Chapter 17 – Breathing and Exchange of Gases
NCERT Biology Class 11 Breathing and Exchange of Gases
Class 11 Biology covers vast topics, thus, it is important for students to dedicate a fixed time to revise all the concepts discussed in the textbook. They must also attempt the questions given at the end of the chapter as a part of the revision strategy.
However, finding the right answers to textbook questions is usually a difficult and time-consuming task. Students need not worry, as Extramarks provides solutions to the questions of Class 11 NCERT Biology Chapter 17 – Breathing and Exchange. The solutions have been prepared by subject matter experts, which makes them reliable.
The solutions provided are precise and clear. The NCERT Solutions for Class 11 Chapter 17 – Breathing and Exchange by Extramarks will help students save ample time, which can be used for solving sample papers, attempting mock tests, or revising other topics.
NCERT Solutions for Class 11 Biology Chapter 17
Chapter 17 of Class 11 Biology covers many theories, definitions, and explanations of concepts related to breathing and the exchange of gases. The chapter contains a number of illustrations and diagrams that explain the human respiratory system, transportation of carbon dioxide, and many other processes involved in respiration. The hazardous effects of air pollution and smoking are taught to the students so that they become aware and could be responsible towards nature and take care of their health as well. Students will also be taught the importance of diet and the beneficial effects brought by following a good diet plan.
There are practice questions given at the end of the chapter to help students gauge their understanding of whatever they have read so far in Chapter 17. If students are looking for accurate answers to these questions or need to cross-check the answers that they have written, Chapter 17 Biology for Class 11 NCERT Solutions by Extramarks is the learning aid to rely upon.
Marks Distribution of NCERT Solutions Class 11 Biology Chapter 17 Breathing and Exchange of Gases
Unit V, Human Physiology, consists of seven chapters altogether, including the chapter on Breathing and Exchange of Gases. The entire unit carries 18 marks in the final examinations. It has a weightage of 20 percent in NEET.
Benefits of NCERT Solutions Class 11 Biology Chapter 17 Breathing and Exchange of Gases
Students will be well-prepared and confident after studying the Chapter 17 Biology Class 11 NCERT Solutions. They will be able to provide well-structured and concise answers in their examination. Other benefits of NCERT Solutions include:
- The answers have been compiled by subject experts, which makes them a reliable source for students.
- The textbook solutions are answered in a detailed way and diagrams are drawn wherever necessary to enhance the students’ understanding of the concepts.
- The answers are written according to the guidelines given by CBSE.
- The solutions have all the answers in one place and hence can be used for a quick revision or practise by students before their examinations.
Lenticels are involved in
- Gaseous exchange
- Food transport
Ans. Gaseous exchange
Aerosols having carbon and fluorine compounds are chiefly released by
Q.1 Define vital capacity. What is its significance?
Vital capacity refers to the volume of air a healthy person can inhale after a forced exhalation or the volume of air a person can exhale after a forced inhalation. It is the sum of Expiratory Reserve Volume (ERV), Tidal Volume (TV), and Inspiratory Reserve Volume (IRV). A normal adult person has a vital capacity of 3-5 litres.
Significance: Vital capacity is highest when physiological competence of the body is highest. It goes down as incompetence increases and becomes zero when respiration ceases. It implies that more the vital capacity, healthier is the body. Also, it helps in getting rid of the foul air and aids in supplying fresh air. Thus, the vital capacity enhances the exchange of gases between the body tissues and the environment.
Q.2 State the volume of air remaining in the lungs after a normal breathing.
The volume of air that remains in the lungs after normal breathing is called FRC (functional residual capacity). This includes expiratory reserve volume (ERV, additional volume of air, a person can exhale by a forcible exhalation) and residual volume (RV, the volume of air remaining in the lungs even after a forcible exhalation). In a normal individual, ERV is about 1000 to 1100 mL while RV is about 1100 to 1200 mL.
Since, FRC = ERV + RV
FRC = 1000 (or 1100 mL) + 1100 (or 1200) mL
= 2100 or 2300 mL.
Thus, the volume of air remaining in the lungs after normal breathing is around 2100 mL to 2300 mL.
Q.3 Diffusion of gases occurs in the alveolar region only and not in the other parts of respiratory system. Why?
The gaseous exchange (exchange of O2 and CO2) occurs in our body by simple diffusion between the blood capillaries around the alveoli and gases present in the alveoli. Alveoli are made up of thin and highly permeable layers of squamous epithelial cells. The reasons for gaseous diffusion in the alveolar region are as follows:
- Concentration and pressure: Diffusion is a concentration and pressure-dependent process. The barrier between the capillaries and alveoli is thin and it facilitates the gaseous diffusion from the region of higher to lower partial pressure. Pressure contributed by an individual gas in gaseous mixture is called its partial pressure. The partial pressure of O2 is high in the air present inside the lungs as compared to deoxygenated blood in lung capillaries. It means that there is a concentration gradient for O2 between the lungs and blood. Thus, O2 can easily diffuse from alveolar air into the blood of alveolar capillaries. A reverse concentration gradient is present for CO2, thus diffusion of CO2 takes place in the opposite direction.
- Nature of the membranes at the site of exchange: The region where diffusion takes place is made up three major layers namely; the thin squamous epithelium of alveoli, the endothelium of alveolar capillaries and the basement substance in between them. The total thickness of these three layers is less than a millimetre which makes it ideal to act as a site for the diffusion of gases.
Q.4 What are the major transport mechanisms for CO2? Explain.
Blood is the medium for transport of CO2. There are three main ways by which CO2 is transported in the body:
- By red blood cells (RBCs): The haemoglobin present in the RBCs carry about 20-25% CO2 as carbamino-haemoglobin. Haemoglobin transports CO2 as well as O2 and this transport of CO2 depends upon the partial pressure of these gases. If there is high partial pressure of O2, then CO2 is dissociated and O2 is acquired by haemoglobin (like in lungs where O2 is present in abundance). When oxygenated blood reaches the tissues, due to the high partial pressure of CO2, haemoglobin loses O2 and acquires CO2. This CO2 is transported to lungs for its exchange with O2.
- By RBCs and plasma as bicarbonate ion: Nearly 70% of CO2 is transported in the form of bicarbonate ions. RBCs contain a very high amount of an enzyme called carbonic anhydrase. This enzyme is also present in minute amounts in plasma. A large part of CO2, as it diffuses into the blood plasma, combines with water to form carbonic acid with the help of enzyme carbonic anhydrase. Thereafter, the carbonic acid dissociates into bicarbonate and hydrogen ions by the action of the same enzyme. Thus, CO2 is transported in the form of bicarbonate ions.
- Approximately 7% of CO2 is carried in dissolved state through plasma. CO2 combines with water to form carbonic acid.
Q.5 What will be the pO2 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
(ii) pO2 higher, pCO2 lesser
In the atmosphere, O2 is present in large quantity and thus, its partial pressure is higher (159 mm Hg) than pO2 in alveolar air (104 mm Hg).
The pCO2 is lesser in atmosphere (0.3 mm Hg) as compared to pCO2 in alveoli (40 mm Hg).
Q.6 Explain the process of inspiration under normal conditions.
The process of taking the air from outside the body into the lungs is called inhalation or inspiration. The process of inspiration involves the generation of the pressure gradient between the atmosphere and the lungs. Inspiration takes place when the pressure within the lungs is less (negative pressure) than the atmospheric pressure. The process of inspiration involves the following steps:
- A negative pressure is generated within the lungs with the help of diaphragm and intercostal muscles (internal and external intercostal muscles)
- Contraction of diaphragm increases the volume of the thoracic chamber in the anteroposterior axis.
- Contraction of external intercostal muscles increases the volume of the thoracic chamber in the dorsoventral axis by lifting up the ribs and the sternum.
- Increase in thoracic volume results in an increase in the pulmonary volume.
- Increased pulmonary volume results in a decrease in intra-pulmonary pressure as compared to atmospheric pressure.
- A decrease in intra-pulmonary pressure (negative pressure as compared to atmospheric pressure) allows the air to move into the lungs, i.e., inspiration or inhalation.
Q.7 How is respiration regulated?
Respiration in human beings is a regulated process. It is regulated by the neural system according to the demands of the body tissues. It is mainly controlled by two regulatory regions present in the brain. These are:
(a) Respiratory rhythm centre: It is present in the medulla region of the brain and is mainly responsible for regulating the process of respiration. The areas adjacent to the respiratory rhythm centre are highly chemo-sensitive. They can sense the CO2 and H+ levels, whose increase activates the respiratory rhythm centre. Once activated, this centre adjusts the respiratory process, which helps in the elimination of CO2 and H+ from the body. Receptors associated with the aortic arch and carotid artery also sense the change in CO2 and H+ concentration and send signals to the respiratory rhythm centre to adjust the respiratory process.
(b) Pneumotaxic centre: It is present in the pons region of the brain. This centre can moderate the function of respiratory rhythm centre and reduces the duration of inspiration, which in turn changes the respiratory rate.
Q.8 What is the effect of pCO2 on oxygen transport?
Oxygen binds to haemoglobin reversibly to form oxyhaemoglobin, which transports throughout the body to supply oxygen to different tissues. The binding of one molecule of haemoglobin with four molecules of oxygen depends on the partial pressure of oxygen (pO2). However, the partial pressure of CO2 also plays a significant role in the binding of oxygen with the haemoglobin molecule and its transport from lungs to tissues and vice-versa.
In alveoli, the pO2 is high but pCO2 is low. Thus, oxygen binds to haemoglobin and oxyhaemoglobin is formed. It transports the oxygen to body tissues. However, in tissues, the pCO2 is higher than pO2. Thus, O2 dissociates from haemoglobin and is released. Here, CO2 binds to haemoglobin to form carbamino-haemoglobin. CO2 Is thus transported to the lungs and is released in the lung cavity in exchange of O2. Thus, it can be stated that the affinity of haemoglobin for O2 increases as pCO2 decreases.
Q.9 What happens to the respiratory process in a man going up a hill?
As a person goes up a hill (that is, at higher altitude), the level of O2 in the atmosphere decreases. So, less O2 is available for breathing and O2 level in the blood starts to decline. It results in an increase in the respiratory rate so as to meet the O2 demands of the body. Heart beat also increases to increase the supply of blood to the tissues so that every body tissue gets sufficient O2.
Q.10 What is the site of gaseous exchange in an insect?
Insects have specialized structures called spiracles arranged in a series on the sides of its body. These are small openings through which the oxygen-rich air enters into the body. Spiracles are connected to a network of tubes called trachea which diffuses oxygen into the cells of the body. The transport of CO2 occurs in reverse direction, that is, from the trachea to the spiracles. Thus, the gaseous exchange occurs in the insects through the tracheal system.
Q.11 Define oxygen dissociation curve. Can you suggest any reason for its sigmoidal pattern?
Oxygen is transported in the blood by haemoglobin in the form of oxyhaemoglobin. Each haemoglobin molecule can carry a maximum of four O2 molecules. Binding of oxygen to haemoglobin is primarily affected by the partial pressure of O2 (pO2). However, the partial pressure of carbon dioxide (pCO2), H+ concentration and temperature also affect the binding of oxygen to haemoglobin. When the partial pressure of oxygen is high like in alveoli, haemoglobin binds with oxygen and forms oxyhaemoglobin. However, in tissues where pO2 is low, oxygen dissociates from oxyhaemoglobin. The per cent saturation of haemoglobin with oxygen at various pO2 can be studied using the oxygen dissociation curve. The oxygen dissociation curve is a sigmoid curve which is obtained by plotting the percentage saturation of haemoglobin with O2 against pO2.
The oxygen dissociation curve is sigmoid in shape because the binding of oxygen molecules to haemoglobin is co-operative. It means that binding of first O2 molecule to the haemoglobin increases the affinity of haemoglobin for another oxygen molecule. As a result, the haemoglobin attracts more oxygen and thus, the graph showing the percentage saturation of haemoglobin with O2 against pO2 appears sigmoid.
Q.12 Have you heard about hypoxia? Try to gather information about it, and discuss with your friends.
Hypoxia is a condition, wherein the tissues are not oxygenated adequately due to decreased supply of oxygen to the lungs. The oxygen deprivation can have severe adverse effects on various body cells and thus, several important biological processes get hampered. In general, hypoxia results in a pathological condition. There are various types of hypoxia depending upon the reason of inadequate oxygen supply to the body:
- Hypoxic hypoxia or generalized hypoxia: This results because of an inadequate saturation of blood with oxygen due to a reduced supply of oxygen in the air, decreased lung ventilation or respiratory disease.
- Anaemic hypoxia: This is due to decreased haemoglobin concentration.
- Stagnant hypoxia: This is due to poor circulation of the blood.
- Histotoxic hypoxia: This occurs when the tissues are unable to use oxygen due to cyanide or carbon monoxide poisoning.
Q.13 Distinguish between
(a) IRV and ERV
(b) Inspiratory capacity and expiratory capacity.
(c) Vital capacity and Total lung capacity.
(a) IRV and ERV:
|IRV (Inspiratory Reserve Volume) is the additional volume of air that a person can inhale by a forceful inspiration.||ERV (Expiratory Reserve Volume) is the additional volume of air that a person can exhale by a forceful expiration.|
|It is approximately 2500-3500 mL.||It is approximately 1000-1100 mL.|
(b) Inspiratory capacity and expiratory capacity:
|Inspiratory capacity||Expiratory capacity|
|Inspiratory capacity is the volume of air that can be inhaled after a normal expiration.||Expiratory capacity is the volume of air that can be exhaled after a normal inspiration.|
|It includes tidal volume and IRV.||It includes tidal volume and ERV.|
(c) Vital capacity and Total lung capacity:
|Vital capacity||Total lung capacity|
|Vital capacity refers to the volume of air a healthy person can inhale after a forced exhalation or the volume of air a person can exhale after a forced inhalation.||Total lung capacity is the total volume of air present in the lungs after a forced inhalation.|
|It includes ERV, IRV, and tidal volume.||This includes ERV, IRV, residual volume and tidal volume.|
|It is about 4000 mL.||It is about 5000-6000 mL.|
Q.14 What is Tidal volume? Find out the Tidal volume (approximate value) for a healthy human in an hour.
Tidal volume is the volume of air that is inhaled or exhaled during normal respiration. It is about 500 mL. A healthy person breathes about 12-16 times in a minute.
The approximate value of tidal volume for a healthy human per hour can be calculated as follows:
The tidal volume of a healthy human in an hour = Tidal volume per breath X Number of times an adult human being breathes per minute X 60 minutes
= 500 mL X 12-16 times per minute X 60 minutes
= 3,60,000 – 4,80,000 mL
FAQs (Frequently Asked Questions)
1. How is respiration regulated?
Both the neurological and chemical systems are involved in respiration. The Medulla Oblongata and Pons Varolii consist of a large cluster of neurons that forms the respiratory centre of the brain. The rate and depth of breathing come under the control of the respiratory system.
The dorsal respiratory group of neurons is found in the dorsal part of the medulla oblongata. The main function of these neurons is the control and regulation of inspiration.
In the ventrolateral region of the medulla oblongata, there are a series of neurons called the ventral group. These neurons can both cause inspiration and exhalation.
Respiration is chemically controlled by chemoreceptors in the carotid and aortic bodies. Excess amounts of carbon dioxide or hydrogen ions stimulate the respiratory centre in the brain which in turn increases the inspiratory and expiratory impulses to the respiratory muscles. An increase in carbon dioxide causes acidosis. The role of oxygen in the respiratory rhythm is very little.
2. Define the oxygen dissociation curve in Chapter 17 of Class 11 Biology. Can you suggest any reason for its sigmoidal pattern?
A curve known as the oxygen haemoglobin dissociation curve depicts the relationship between partial pressure of oxygen (pO2) and percent saturation of haemoglobin with oxygen (O2) (also called oxygen dissociation curve)
The sigmoidal pattern of the haemoglobin oxygen dissociation curve is because of two features that are responsible for the transport of oxygen. The two features are as follows:
- The comparatively flat segment of the curve depicts the considerable increase in oxygen tension beyond pO2 of 70-80 mm Hg; minimum oxygen loss from haemoglobin occurs.
- Any additional increase in drops of pO2 below 40 mm results in a disproportionately higher release of oxygen from haemoglobin. It causes the curve to appear sigmoid and results in a steeper portion of the curve.
3. Explain the process of inspiration under normal conditions as discussed in Chapter 17 of Class 11 Biology
When fresh air enters the lungs, this process is known as inspiration. The diaphragm, intercostal muscles, and abdominal muscles all play a vital role. The most important muscles involved in the process of inspiration are the diaphragm and the external intercostal muscles. The diaphragm and intercostal muscles contract, thereby increasing the volume of the thoracic cavity. Relaxation of the abdominal muscles occurs during inspiration, allowing the diaphragm to compress the abdominal organs. As a result of this, the overall volume of the thoracic cavity grows, and the air pressure in the lungs decreases. Because of higher pressure outside the body, the air now flows into the lungs. This is the order in which air flows during inspiration.
4. According to Chapter 17 of Class 11 Biology, why does diffusion of gases occur only in the alveolar region and not in the other parts of the respiratory system?
For the proper diffusion of gases, the region should meet the following criteria to be capable enough for the process to take place. They are:
- The membrane should be permeable to gases and should be thin and moist too.
- It should have a large surface area.
- It should have high vascularity.
All these criteria are met by the alveolar membrane and hence it is the most suitable part to carry out the diffusion of gases over the other parts of the respiratory system.
5. Explain the effects of climbing a hill on the respiratory system of a man
As the altitude increases, the rate of oxygen in the atmosphere decreases. As the man climbs higher, it becomes difficult for him to breathe due to the decrease in oxygen supply to the blood. Because of the lower oxygen supply to the blood, the respiratory rate increases, making it difficult to breathe. The blood is in constant need of oxygen. To supply the blood with oxygen, the heart rate of the man also increases.
6. Briefly explain the site of gaseous exchange in an insect
Insects have a trachea system which is a combination of tubes. The exchange of gases happens in this trachea system. Spiracles are small openings present on the side of the insect’s body which play an important role in absorbing oxygen for the body. The spiracles are connected to the trachea. The oxygen is transported to the trachea via the spiracles. The oxygen starts to diffuse in the body, whereas carbon dioxide is taken out of the body. From the cell of the body, CO2 travels to the trachea and exits the body through the spiracles.