Notes for NCERT Class 11 Biology Chapter 14 Breathing and Exchange of Gases: Breathing (ventilation) is a process of moving air into and from the lungs so that the exchange of gases can be taken place with the internal environment. The main purpose is to expel carbon dioxide and take in oxygen. Respiration is a process in which the cells of an organism get energy by the oxidation or burning of the glucose molecules when we inhale oxygen from the air. The liberated energy is used up by our body to perform some functions like muscle contraction, nerve impulse transmission, protein synthesis, etc. There are some organs involved in these processes which perform specific functions.
Class 11 Biology Chapter 14 Breathing and Exchange of Gases: Explains the respiratory system is the network of many organs which help in breathing. It comprises the airways, lungs and blood vessels. These work together to transport oxygen throughout the body and clean out the waste gases like carbon dioxide. The respiratory system performs many functions. It helps to inhale (breathe in) and exhale (breathe out), allows us to talk and to smell. It also helps to deliver oxygen to the cells, warms up the air according to the body’s temperature and moisturises it to the humidity level according to the need. Removal of gases waste, including carbon dioxide, is another job, it performs. Some conditions may affect the organs and tissues of the respiratory system. Some may be developed due to the irritants we inhale from the air, including viruses or bacteria which cause infection.
Breathing
Breathing is a physical process that involves the exchange of gases, i.e. oxygen and carbon dioxide. It takes place outside the cells (intercellular) without enzymes. The energy is not liberated during the process.
Respiration
Respiration is a biochemical process that involves the oxidation or burning of glucose molecules. It takes place within a cell (intracellular) where some respiratory enzymes are required. Therefore, also known as cellular respiration. The energy is liberated during the process.
Also Read: Difference between Respiration and Breathing
Respiratory Organs
In some unicellular organisms, gaseous exchange can be done by diffusion, in which their whole body or the cell comes in direct contact with the air, e.g., the unicellular aquatic organisms, consume oxygen dissolved in the surrounding water medium. In multicellular organisms, well-differentiated or elaborated organs are involved to carry out the same process.
Some Examples of Respiratory Organs
Respiratory Organs |
Examples |
General Body Surface |
Sponges, Coelenterates, Flatworms |
Moist Skin |
Earthworms, Frogs |
Tracheal Tubes |
Insects |
Lungs |
Reptiles, Birds, Mammals |
Gills |
Aquatic Arthropods, Molluscs, Fishes |
Human Respiratory System
The human respiratory system is divided into the upper respiratory tract and the lower respiratory tract which, comprise some organs which are listed below along with their description and functions:
The Upper Respiratory Tract
Structure |
Description |
Function |
Nares/Nostrils |
Openings into the nasal cavities |
Passage of air into nasal cavities |
Nasal Cavities |
Hollow spaces in the nose |
Filter, warm and moisten the air |
Pharynx |
Lies between the nasal cavity and the larynx. It forms the common passage for food and air. |
Makes a connection to the surrounding regions |
Glottis |
Opening into the larynx. It can be covered by a cartilaginous flap called epiglottis to prevent the entry of food into the larynx |
Passage of air into the larynx |
Larynx |
It is cartilaginous and has vocal cords (voice or sound box) |
Production of sound |
The Lower Respiratory Tract
Structure |
Description |
Function |
Trachea |
A flexible tube connects the larynx with the bronchi. They have cartilaginous rings which prevent them from being collapsed |
Passage of air into bronchi |
Bronchi |
Paired tubes that enter the lungs |
Passage of air to lungs |
Bronchioles |
Branched tubes originated from the bronchi to the alveoli (air sacs). They are divided into primary, secondary and tertiary bronchioles, according to the fine main branch or their fine divisions |
Passage of air to each alveolus |
Lungs |
Soft and cone-shaped organs |
Contain alveoli and provide a rich supply of blood as they contain blood vessels |
Alveoli |
Grapes-like or vascularised bag-like structures. |
Ultimate site of respiration or exchange of gases |
Human has two lungs, enveloped by a double-layered membrane, known as pleura. In between the pleura, pleural fluid is present, which reduces friction on the surface of the lungs. The outer pleural membrane lies close to the thoracic lining, while the inner pleural membrane lies close to the surface of the lungs.
Steps Involved in Respiration
- Breathing or pulmonary ventilation, in which oxygen from the atmosphere is drawn in and CO2-rich air from the alveoli releases.
- Diffusion of gases (O2 and CO2 ) occurs at the alveolar membrane.
- Transportation of gases by the blood.
- Diffusion of O2 and CO2 occurs between blood and tissues.
- The utilisation of O2 by the cells and release of CO2 (cellular respiration).
Mechanism of Breathing
The mechanism of breathing involves the events that occur during two processes, i.e. inhalation or inspiration and exhalation or expiration. The events involved are given below:
Events During Inspiration |
Events During Expiration |
The respiratory centre initiates the stimulus/stimuli. |
The respiratory centre terminates the stimulus/stimuli. |
Diaphragm and expiratory muscles contract. |
Diaphragm relaxes and internal intercostal muscles contract. |
Thoracic volume increases because the chest wall expands. |
Thoracic volume decreases because the chest wall contracts. |
Intra-pulmonary pressure (inside the lungs) is reduced. |
Intra-pulmonary pressure (inside the lungs) is increased. |
Alveolar pressure decreases more than atmospheric pressure. |
Alveolar pressure increases more than atmospheric pressure. |
Air is taken inside due to the expansion of the alveoli. |
Air is given out due to the contraction of the alveoli. |
Air rushes into the alveoli until the alveolar pressure equalizes to the atmospheric pressure and the alveoli become inflated. |
Air rushes out of the alveoli until the alveolar pressure equalizes to the atmospheric pressure and the alveoli become deflated. |
Respiratory Volumes and Capacities
Respiratory Volume |
Definition |
Capacities |
Tidal Volume (TV) |
It is the volume of the air which is inspired or expired during a normal respiration |
It is approx. 500 mL. A healthy person can inspire or expire approx. 6000-8000 mL of air per minute |
Inspiratory Reserve Volume (IRV) |
It is the additional volume of the air which, a person can inspire by a forcible inspiration |
It is approx. 2500 mL to 3000 mL |
Expiratory Reserve Volume (ERV) |
It is the additional volume of the air which, a person can expire by a forcible expiration |
It is approx. 1000 mL to 1100 mL |
Residual Volume (RV) |
It is the volume of the air which remains in the lungs even after a forcible expiration |
It is approx. 1100 mL to 1200 mL |
Inspiratory Capacity (IC) |
It is the total volume of the air a person can inspire after a normal expiration |
This includes tidal volume and inspiratory reserve volume ( TV+IRV), i.e. 9700 mL |
Expiratory Capacity (EC) |
It is the total volume of the air a person can expire after a normal inspiration |
This includes tidal volume and expiratory reserve volume (TV+ERV), i.e. 8000 mL |
Functional Residual Capacity (FRC) |
It is the volume of the air that remains in the lungs after a normal expiration |
This includes ERV+RV, i.e. 2100 mL |
Vital Capacity (VC) |
It is the maximum volume of the air which, a person can breathe in after a forced expiration. This includes ERV, TV and IRV or the maximum volume of the air a person can breathe out after a forcible inspiration |
It is approx. 10000 mL |
Total Lung Capacity |
It is the total volume of the air which is present in the lungs at the end of a forcible inspiration. This includes RV, ERV, TV and IRV or vital capacity + residual volume |
It is approx. 11000 mL |
Also Read: Respiratory Volumes and Capacities
Exchange of Gases
During the exchange of gases, oxygen is transported from the lungs to the bloodstream. At the same time, carbon dioxide is passed from the blood to the lungs. This happens in the lungs between the alveoli and a network of blood vessels (capillaries), which are located in the walls of the alveoli. The diagrammatic explanation of the exchange of gases is given below:
Transport of Gases
Blood is the medium for the transportation of O2 and CO2. The transport of both gases is discussed below:
Transport of Oxygen
About 97 per cent of the O2 is transported by RBCs in the blood, and the remaining 3 per cent is transported in the dissolved state through plasma.
- O2 can be bound with haemoglobin to form oxyhemoglobin.
- The partial pressure of CO2, hydrogen ion concentration and temperature are the factors which interfere with this binding.
- A sigmoid curve is formed when the percentage of the saturation of haemoglobin with O2 is plotted against the pO2. This formed curve is known as the Oxygen dissociation curve.
- Factors Favourable for the Formation of Oxyhemoglobin: In the alveoli, pO2 is high, pCO2 is low, H+ concentration is less and temperature is lower.
- Factors Favourable for the Dissociation of Oxyhemoglobin: In the tissues, pO2 is low, pCO2 is high, H+ concentration is high and temperature is high.
- This shows that O2 is bound to haemoglobin in the lung (surface) and becomes dissociated in the tissues.
Also Read: Transport of Oxygen
Transport of Carbon Dioxide
Approx. 20-25 per cent of the CO2 is transported by RBCs by binding with it, to form carbamino-haemoglobin, 70 per cent is carried as bicarbonates and around 8-9 per cent of CO2 is transported in a dissolved state through plasma.
- The formation of carbamino-hemoglobin is related to pCO2 which is a major factor that affects the binding.
- Factors Favourable for the Binding of Carbon Dioxide: In the tissues, high pCO2 and low pO2 are required.
- Factors Favourable for the Dissociation of Carbon Dioxide: In the alveoli, low pCO2 and high pO2 are required.
- CO2 bound to haemoglobin from the tissues is transported to the alveoli.
- RBCs have a high concentration of carbonic anhydrase enzyme and low quantities of it are present in the plasma.
- In the tissues with high pCO2 due to catabolism, CO2 diffuses into the blood (RBCs and plasma) and forms HCO3– and H+.
- In the alveoli, with low pCO2, the reaction is followed in the reverse direction which leads to the formation of CO2 and H2O.
- CO2 is formed as the bicarbonates in the tissues and transported to the alveoli where it is released as CO2.
Also Read: Transport of Carbon Dioxide
Regulation of Respiration
Respiration is regulated by two mechanisms, i.e. nervous mechanism and the chemical mechanism. In the nervous regulation, respiratory centres are present in the medulla oblongata which senses the level of oxygen and carbon dioxide in the blood and sends impulses by the respiratory muscles. The pneumatic centre can change the function of the respiratory rhythm centre by signalling in order to reduce the rate of inspiration. The diagrammatic representation of the regulation of respiration is given below:
Disorders of the Respiratory System
Respiratory Disorder |
Description |
Asthma |
It is a chronic lung disorder which is caused by the inflammation and tightness of the muscles around the airways, because of which breathing can be difficult. |
Emphysema |
It is a lung disorder which causes shortness of breath because the air sacs in the lungs (alveoli) are damaged |
Occupational Respiratory Disorders |
These are the lung disorders that have been caused by long-term exposure to some irritants in the workplace |
Also Read: Disorders of Respiratory Systems
FAQs on Breathing and Exchange of Gases
Q1: What is Residual Volume?
Answer:
It is the volume of the air which remains in the lungs even after a forcible expiration. It is approx. 1100 mL to 1200 mL
Q2: Write the Steps Involved in Respiration.
Answer:
The steps involved in respiration are given below:
- Breathing or pulmonary ventilation in which oxygen from the atmosphere is drawn in and CO2 rich air from the alveoli releases out.
- Diffusion of gases (O2 and CO2 ) occur at the alveolar membrane.
- Transportation of gases by the blood.
- Diffusion of O2 and CO2 occur between blood and tissues.
- Utilisation of O2 by the cells and release of CO2 (cellular respiration).
Q3: What is the Name of the Respiratory Organs Present in Molluscus?
Answer:
Gills are the rrespiratory organs present in Molluscus.