CBSE Class 11 Biology Revision Notes Chapter 17

CBSE Class 11 Biology Revision Notes Chapter 17 – Breathing and Exchange of Gases

Class 11 Biology Chapter 17 involves the study of Breathing and Exchange of Gases. In this chapter, students study  respiration, steps of respiration, mechanism of breathing, exchange of gases, transportation of gases, etc. 

The revision notes for this chapter help students to have an in-depth and thorough explanation of the chapter. The notes are prepared by subject experts  following the latest CBSE curriculum. The language used in the revision notes is very simple and easy to understand which helps students to comprehend all the important topics covered in the chapter easily.

Revision Notes for CBSE Class 11 Biology Chapter 17 – Download

Respiration

The process of taking oxygen from the atmosphere and producing carbon dioxide by the body cells is known as respiration. There are two processes: 

1. Breathing
2. Gaseous exchange along with its transport

• The process of transportation of air in and out of the lungs is known as breathing. Breathing involves inspiration and expiration.
• Depending upon the level of organization and habitats in a group of animals, the mechanism of breathing varies in different organisms. . Lower invertebrates For instance, in coelenterates, sponges, flatworms, etc.  oxygen is exchanged with carbon dioxide by simple diffusion over the whole body surface.

Organisms and Their Respiratory Organs

Let’s take a look at some organisms and their respiratory organs:

• The human respiratory system is divided into various parts such as the nostrils, nasal passage, larynx, pharynx, trachea, bronchi, and lungs.
• The openings just above the upper lips are called  nostrils. Through the nasal passage, these nostrils lead to the nasal chamber.
• The nasal chamber is extended into the nasopharynx, which is a portion of the pharynx. It is a passageway for air and food.
• The nasopharynx extends through the larynx region into the trachea.
• The cartilaginous larynx is the soundbox helping in the production of sound.
• Epiglottis helps in preventing food from entering the larynx. It is a cartilaginous flap.
• The windpipe, also called trachea, opens to the mid-thoracic cavity and divides at the level of the 5th thoracic vertebra into the right and left primary bronchi. The primary bronchi are divided into multiple primary bronchioles, which are further divided into two and eleven alveolar ducts.
• The bag-like structures are called alveoli. They are the basic units of gas exchange in the lungs.
• Lungs compose the whole network of bronchi, bronchioles, and alveoli.
• Two lungs in the human body are covered by double-layered pleura having pleural fluid between them.
• Lungs are present in the thoracic chamber. It is anatomically an airtight chamber.
• The thoracic chamber is made up of:

1. Vertebral column at dorsal side.
2. Ventrally my sternum.
3. Ribs at the lateral side.
4. On the lower side is a dome-shaped diaphragm.

Steps of Respirations

• Pulmonary ventilation or breathing process involves drawing oxygen from the atmospheric air inside and releasing carbon dioxide rich in alveolar air outside.
• Across the alveolar membrane, diffusion on both oxygen and carbon dioxide.
• Blood transports the gases throughout the body cells.
• Between blood and tissues of the body, there is a diffusion of oxygen and carbon dioxide.
• For catabolic reactions, cells make use of oxygen and result in the release of carbon dioxide.

Mechanism of Breathing

Two stages are involved in the mechanism of breathing:

1. Inspiration (air is drawn inside)
2. Expiration (Alveolar air is released outside)

• The first breathing stage is inspiration, also called pulmonary ventilation. It involves the movement of air into and out of the lungs.
• Between the ribs, there are Intercostal muscles. These play an important role in breathing.
• The movement of the diaphragm initiates inspiration. To lift the ribs and the sternum, the external intercostal muscle contracts. Ribs move downward and upward directions, and due to the movement of the ribs, the diameter of the thoracic cavity increases. Into the lungs, a negative pressure develops, and air rushes inside them.
• External intercostal muscles get relaxed in case of expiration or exhalation. The ribcage moves downward and upward, reducing the activity of the thoracic. Positive pressure is caused due to the reduced volume that results in exhalation.
• With the help of additional muscles in the abdomen, humans can increase the strength of inspiration and expiration. A healthy person breathes 12-16 times per minute on average. A spirometer is used to determine the volume of air involved in breathing movements.

Respiratory Volumes and Capacities

Respiratory volumes and capacities are expressed in the following ways:

• Tidal Volume (TV): During normal respiration, the amount of air inspired or expired is known as  tidal volume. It is approximately 500ml. A healthy human being inspires or expires 6000 to 8000 ml in a minute.
• Inspiratory Reserve Volume(IRV): The extra volume of air inhaled into the lungs during maximal inspiration is called Inspiratory Reserve Volume.
• Expiratory Reserve Volume (ERV): The maximum amount of air expelled out of the lungs during forcible expiration is known as Expiratory Reserve Volume. It is 1000 to 1100ml.
• Residual Volume (RV): Residual Volume is measured as the volume of air remaining in the lungs after forced expiration.
• Vital Capacity (VC): The maximum volume of air moved in and out of the lungs is called vital capacity. 

VC = Tidal volume + IRV + ERV

• Inspiratory Capacity (IC): Inspiratory Capacity is a person’s capacity to inspire the amount of air after normal expiration. It is → (IRV + TV)
• Expiratory Capacity (EC): Expiratory Capacity is the capacity of a person to expire the amount of air after normal expiration. It is (TV + ERV)
• Functional Residual Capacity (FRC): After a normal expiration, the volume of air in the lungs is termed Functional Residual Capacity. It is (ERV + RV).
• Total Lung Capacity: At the end of the forced inspiration, the accommodation of air volume in the lungs is known as total lung capacity. It is VC + residual volume.

Exchange of Gases

The exchange of gas takes place in the alveoli, which is the primary site. The simple diffusion process is the reason behind the exchange of gases.

• Blood helps to travel the oxygen throughout the body.
• Based on partial pressure, oxygen is released into the body tissues. Atmospheric air is the mixture of a large number of gases. The total pressure of the atmospheric gas is contributed individually by each gas. The individual gas pressure contributing to the atmospheric pressure is known as partial pressure. The difference between partial pressure determines the movement of the air from one place to another. The partial pressure of oxygen is more in alveoli than in the human body tissues therefore gradient oxygen is transported to the body tissues. In the tissues, the partial oxygen is low, so the blood becomes deoxygenated.
• Partial carbon dioxide is high in tissues. Blood takes the carbon dioxide from the tissues and releases it in alveoli where partial carbon dioxide is low.
• Three layers make up the diffusion layer of alveoli:

1. Thin squamous epithelium.
2. Endothelium.
3. Fused basement membrane.

Transport of Gases

• Throughout the body, oxygen and carbon dioxide is carried by the blood.
• The RBC carries 97% of the oxygen in the blood. 3% of the oxygen is carried in the dissolved state.
• Carbon dioxide is majorly transported in a dissolved state through the plasma present in the blood. 70% of the Carbon dioxide is carried in bicarbonate form. 7% of carbon dioxide is carried in a dissolved state, and RBC transports 20-25%.
• Oxygen is carried in the bound form of haemoglobin, which is a red-coloured iron-containing pigment. Oxyhaemoglobin is formed by binding oxygen with haemoglobin.
  1. One molecule of haemoglobin binds with oxygen molecules. This binding depends upon:
     1. The partial pressure of oxygen
     2. The partial pressure of carbon dioxide 
     3. H+ ion concentration
     4. Temperature
  2. The curve is called oxygen dissociation when the percentage saturation of haemoglobin is plotted against the partial oxygen.
  3. In low temperature, low partial carbon dioxide, high partial oxygen, and less H+ ion concentration shift the curve to the right indicating oxyhaemoglobin formation. On the other hand, in high carbon dioxide, low oxygen, and basic pH, the high-temperature curve shifts to the left, indicating the dissociation of oxygen with haemoglobin.

Transport of Carbon Dioxide

Carbon dioxide is transported in the form of carbamino-haemoglobin.

• During high partial carbon dioxide and low partial oxygen in the alveoli, more binding of the carbon dioxide occurs, and hence dissociation of carbon dioxide with carbamino-haemoglobin takes place.
• Carbon dioxide diffuses into the blood and forms HCO3– and H+ ions. Under the action of the enzyme carbonic anhydrase

CO2 + H2O ⇄ H2CO3 ⇄ HCO3– + H+

• This reaction proceeds in the opposite direction, where partial carbon dioxide is low.

Regulation of Respiration

The neural system is the system that has the control of respiration.

• In the medulla region in the brain, there is a respiratory rhythm centre responsible for respiration regulation.
• In the pons region of the brain, there are also Pneumotaxic centres present.
• There is a chemosensitive area adjacent to the rhythmic centre, which is highly sensitive to CO2 and H+ ion concentration.

Disorders of Respiration

• Asthma: When there is an inflammation of bronchi and bronchioles, it is known as asthma. Asthma causes wheezing and difficulty in breathing.
• Emphysema: In this condition, alveolar walls get damaged, and as a result, the respiratory surface is decreased. It is a chronic disorder.
• Fibrosis: Fibrosis is an occupational respiratory disorder that is caused by inflammation in the lungs. Inflammation to the lungs is caused due to long-term exposure to dust. This kind of disorder is seen usually in people involved in stone breaking and grinding.