MCQ (Practice) - Respiratory System (Level 1) - Class 11 MCQ

Explanation:
The human trachea is a part of the respiratory system and is responsible for the passage of air to and from the lungs. It is a tube-like structure that is composed of cartilaginous rings.
Reasons why the trachea does not collapse:
- Cartilaginous rings: The trachea is reinforced by a series of C-shaped cartilaginous rings. These rings are made of hyaline cartilage and provide support and rigidity to the trachea, preventing it from collapsing even when there is no air present. The rings are incomplete at the back, allowing flexibility for movements like swallowing.
- Elastic fibers: The walls of the trachea also contain elastic fibers, which allow the trachea to stretch and recoil during breathing movements. These fibers help maintain the shape of the trachea and prevent it from collapsing.
- Mucus production: The trachea is lined with a layer of mucus-producing cells. The mucus helps to keep the trachea moist and traps dust, bacteria, and other foreign particles. This mucus layer also acts as a lubricant, reducing friction as air passes through the trachea.
Overall, the combination of cartilaginous rings, elastic fibers, and mucus production ensures that the human trachea does not collapse even when there is no air in it.

Explanation:
The specialty common in the alveoli of lungs and villi of intestine in mammals is that both provide a large surface area. This large surface area allows for efficient gas exchange and absorption of nutrients.
Reasoning:
1. Alveoli of lungs:
- Alveoli are tiny air sacs located at the end of the bronchioles in the lungs.
- They have a large surface area due to their numerous small sacs and thin walls.
- This large surface area increases the efficiency of gas exchange, allowing oxygen to enter the bloodstream and carbon dioxide to be removed.
2. Villi of intestine:
- Villi are finger-like projections found in the small intestine.
- They have a large surface area due to their numerous folds and microvilli.
- This large surface area increases the efficiency of nutrient absorption by maximizing contact between the food and the absorptive cells of the intestine.
3. Both structures:
- The alveoli and villi have a rich supply of blood vessels and lymph ducts.
- This allows for the transport of oxygen and nutrients from the alveoli and villi to the rest of the body.
- It also allows for the removal of waste products and carbon dioxide.
Conclusion:
The specialty common in the alveoli of lungs and villi of intestine in mammals is that both provide a large surface area, which allows for efficient gas exchange and absorption of nutrients.

The mode of respiration in a rabbit is pulmonary.

Explanation:

A rabbit is a mammal, and like all mammals, it breathes through its lungs. The lungs are the main organs used for respiration in rabbits.

Here are some key points to understand the mode of respiration in rabbits:

1. Pulmonary Respiration:
- Pulmonary respiration refers to the process of breathing through the lungs.
- In this mode of respiration, oxygen is taken in through the respiratory system and carbon dioxide is expelled.
- The respiratory system in rabbits includes the lungs, bronchi, trachea, and diaphragm.
- The lungs are highly efficient organs that extract oxygen from the inhaled air and release carbon dioxide.
- This mode of respiration allows for a high oxygen uptake, which is essential for the rabbit's energy needs.
2. Other Modes of Respiration:
- While pulmonary respiration is the primary mode of respiration in rabbits, they also have other modes of respiration to a lesser extent.
- Mucosal respiration refers to respiration through the moist lining of the respiratory passages, such as the nasal cavity.
- Cutaneous respiration refers to respiration through the skin. While some amphibians rely heavily on cutaneous respiration, rabbits do not have a significant capacity for this mode of respiration.
- Tracheal respiration refers to respiration through small tubes called tracheae, which can be found in some insects and arthropods. Rabbits do not possess tracheae.
Conclusion:
The mode of respiration in rabbits is primarily pulmonary, with the lungs being the main organs used for respiration. Other modes of respiration, such as mucosal, cutaneous, and tracheal respiration, are not significant in rabbits.

The structure which does not contribute to the breathing in mammals is the Larynx.
The larynx, also known as the voice box, is responsible for producing sound and is involved in speech. While it plays a crucial role in vocalization, it does not directly contribute to the breathing process in mammals. Here's a breakdown of the other structures involved in breathing:
1. Diaphragm:
- The diaphragm is a domed-shaped muscle located at the base of the thoracic cavity.
- It separates the thoracic cavity from the abdominal cavity.
- During inhalation, the diaphragm contracts and moves downward, increasing the volume of the thoracic cavity, which allows the lungs to expand and fill with air.
2. Intercostal Muscles:
- The intercostal muscles are located between the ribs.
- They consist of external intercostal muscles and internal intercostal muscles.
- During inhalation, the external intercostal muscles contract, lifting the ribcage and expanding the chest cavity.
- During exhalation, the internal intercostal muscles contract, pulling the ribcage downward and decreasing the volume of the chest cavity.
3. Ribs:
- The ribs are long, curved bones that form the ribcage.
- They protect the vital organs in the thoracic cavity, including the lungs and heart.
- The ribs are attached to the spine at the back and the sternum (breastbone) at the front.
- They provide structural support to the chest and help in the expansion and contraction of the thoracic cavity during breathing.
In summary, while the diaphragm, intercostal muscles, and ribs are all involved in the breathing process in mammals, the larynx is primarily responsible for vocalization and does not directly contribute to the inhalation and exhalation of air.

The tracheal rings are made of hyaline cartilage.
Explanation:
The C-shaped cartilaginous rings supporting the trachea are composed of hyaline cartilage. Hyaline cartilage is a type of connective tissue that is characterized by its translucent appearance and firm yet flexible structure. It is the most common type of cartilage in the body and can be found in various locations, including the trachea, larynx, and rib cage.
The function of these rings is to provide support and maintain the patency of the trachea, preventing it from collapsing during breathing. The C shape of the rings allows flexibility for the trachea to expand and contract during respiration, while still providing structural stability.
Other options given in the question are not correct:
- Fibrous cartilage: Fibrous cartilage is found in the intervertebral discs and pubic symphysis, but not in the trachea.
- Elastic cartilage: Elastic cartilage is found in the external ear and epiglottis, but not in the trachea.
- Calcified cartilage: Calcified cartilage is found in the growth plates of developing bones, but not in the trachea.
Therefore, the correct answer is D: Hyaline cartilage.

Smallest Structure in the Lung of a Rabbit: Alveoli

The smallest structure in the lung of a rabbit is the alveoli. Alveoli are tiny air sacs located at the end of the respiratory bronchioles. They are responsible for the exchange of oxygen and carbon dioxide between the lungs and bloodstream. Here is some more information about the other options:

• Tracheae: The tracheae are the main airways that connect the lungs to the external environment. While they are an important part of the respiratory system, they are larger in size compared to alveoli.


• Bronchioles: Bronchioles are small branches of the bronchi that further divide into smaller airways within the lungs. They play a role in conducting air to the alveoli. Although smaller than tracheae, they are still larger than alveoli.


• Hilum: The hilum is a region on the lung where blood vessels, nerves, and bronchi enter and exit. It acts as a gateway for these structures but is not a specific anatomical structure within the lung itself.

Therefore, among the options given, the smallest structure in the lung of a rabbit is the alveoli.

Rate of breathing in an adult human:
The rate of breathing, also known as respiratory rate, refers to the number of breaths a person takes per minute. The normal respiratory rate for an adult human varies, but it is typically within the range of 12 to 20 breaths per minute. However, during certain situations such as physical exertion or anxiety, the respiratory rate may increase.
Here are the options provided and their respective respiratory rates:
A: 25 - 30/min
- This option suggests a respiratory rate of 25 to 30 breaths per minute, which is higher than the normal range for an adult human.
B: 20-25/min
- This option suggests a respiratory rate of 20 to 25 breaths per minute, which is within the normal range for an adult human.
C: 14-18/min
- This option suggests a respiratory rate of 14 to 18 breaths per minute, which is within the normal range for an adult human.
D: 10-12/min
- This option suggests a respiratory rate of 10 to 12 breaths per minute, which is lower than the normal range for an adult human.
Conclusion:
Based on the provided options, the correct answer is C: 14-18/min. This range falls within the normal respiratory rate for an adult human. It is important to note that the respiratory rate can vary depending on factors such as age, health condition, and activity level. If you have concerns about your respiratory rate, it is recommended to consult a healthcare professional.

Effects of Perforated Diaphragm in a Rabbit

• Introduction: The diaphragm is a dome-shaped muscle that plays a crucial role in the process of breathing. It separates the chest cavity from the abdominal cavity and helps in the expansion and contraction of the lungs.


• Perforated Diaphragm: If the diaphragm of a rabbit is perforated, it means that there is a hole or tear in the diaphragm muscle.


• Effects on Breathing: A perforated diaphragm has a significant impact on the breathing of a rabbit. The consequences can be explained as follows:

1. Increased Difficulty in Breathing:

• A perforated diaphragm leads to a loss of integrity and functionality of the muscle.


• This loss of integrity results in an increased difficulty in breathing for the rabbit.


• The diaphragm is responsible for the movement and expansion of the lungs during inhalation and exhalation.


• With a perforated diaphragm, the normal functioning of the diaphragm is compromised, leading to restricted and labored breathing.

2. Reduced Lung Capacity:

• The perforation in the diaphragm can cause air leakage between the chest and abdominal cavities.


• This leakage disrupts the normal pressure gradient required for efficient lung expansion.


• As a result, the lung capacity of the rabbit is reduced, leading to insufficient oxygen intake and carbon dioxide removal.

3. Respiratory Distress:

• Due to the increased difficulty in breathing and reduced lung capacity, the rabbit may experience respiratory distress.


• Respiratory distress is characterized by rapid and shallow breathing, increased heart rate, and potential cyanosis (bluish discoloration of the skin and mucous membranes).

4. Potential Respiratory Failure:

• If the perforation in the diaphragm is severe or if prompt medical intervention is not provided, the rabbit may experience respiratory failure.


• Respiratory failure occurs when the rabbit is unable to maintain adequate oxygenation and carbon dioxide removal.


• In severe cases, respiratory failure can lead to death if not treated promptly.

Conclusion:

In conclusion, a perforated diaphragm in a rabbit has detrimental effects on its breathing. It leads to increased difficulty in breathing, reduced lung capacity, respiratory distress, and can potentially result in respiratory failure and death if left untreated. Immediate veterinary attention is necessary to address the perforation and provide appropriate treatment to restore normal breathing function.

The glottis is a part of the respiratory system that controls the opening and closing of the vocal cords. It allows air to pass through the larynx and into the trachea during breathing.
The correct answer to the given question is C: Bucco-pharyngeal cavity. The glottis is located in the bucco-pharyngeal cavity, which is the region at the back of the mouth and throat.
Here is a detailed explanation:
1. Glottis: The glottis is the opening between the vocal cords in the larynx. It consists of two vocal folds that vibrate to produce sound during speech or singing.
2. Trachea: The trachea is a tube-like structure that connects the larynx to the bronchi of the lungs. It is responsible for the passage of air into the lungs.
3. Diaphragm: The diaphragm is a dome-shaped muscle located below the lungs. It plays a crucial role in the process of breathing by contracting and relaxing to facilitate inhalation and exhalation.
4. Bucco-pharyngeal cavity: The bucco-pharyngeal cavity refers to the region at the back of the mouth and throat. It includes the oral cavity (mouth) and the pharynx (throat). The glottis is located in this cavity.
5. None of the above: This option is incorrect as the glottis does not open in the trachea or diaphragm.
To summarize, the glottis is the opening in the bucco-pharyngeal cavity, allowing air to pass through the larynx and into the trachea.

The first type of respiration that appeared in primitive organisms was anaerobic respiration. This can be explained by the following reasons:
Lack of Oxygen:
- Anaerobic respiration occurred first because there was little to no oxygen present in the Earth's early atmosphere.
- Oxygen is a byproduct of photosynthesis, which was not yet occurring in primitive organisms.
Simplicity of Anaerobic Respiration:
- Anaerobic respiration is a simpler form of respiration compared to aerobic respiration.
- It does not require the presence of oxygen and can be carried out by small organisms.
Energy Production:
- Although aerobic respiration releases more energy than anaerobic respiration, primitive organisms did not require large amounts of energy.
- Anaerobic respiration provided them with enough energy to survive and carry out basic functions.
Waste Products:
- Anaerobic respiration produces waste products such as lactic acid or ethanol, which can be harmful in high concentrations.
- However, in the early stages of evolution, these waste products were not detrimental to primitive organisms.
Therefore, due to the lack of oxygen, simplicity, sufficient energy production, and non-harmful waste products, anaerobic respiration appeared first in primitive organisms.

Oxyhaemoglobin is an unstable compound because of the physical bonding between oxygen and haemoglobin. Here is a detailed explanation:
1. Oxyhaemoglobin:
- Oxyhaemoglobin is a compound formed when oxygen molecules bind to haemoglobin in the red blood cells.
- It is responsible for transporting oxygen from the lungs to the body tissues.
2. Unstable nature:
- Oxyhaemoglobin is considered unstable because the bonding between oxygen and haemoglobin is reversible.
- It means that oxygen can easily dissociate from the haemoglobin molecule when it reaches the tissues that need oxygen.
3. Physical bonding:
- The bonding between oxygen and haemoglobin is a physical bonding, also known as a weak non-covalent bond.
- The physical bonding occurs due to the attraction between the oxygen molecule (O2) and the iron atom (Fe) present in the haemoglobin molecule.
4. Reversible bonding:
- The physical bonding between oxygen and haemoglobin is reversible, allowing the release of oxygen at the tissue level.
- When the oxygen concentration is low in the tissues, the oxyhaemoglobin dissociates, releasing oxygen for cellular respiration.
5. Importance of reversible bonding:
- The reversible bonding of oxyhaemoglobin allows efficient oxygen delivery to tissues with varying oxygen demands.
- It ensures that oxygen is released where it is needed and that the haemoglobin can pick up more oxygen in the lungs.
Therefore, the correct answer is option C: There is a physical bonding between oxygen and haemoglobin, which makes oxyhaemoglobin an unstable compound.

To find the percentage of O₂ present in inhaled air in man, we need to consider the composition of air.
Composition of air:
Air is a mixture of different gases, including oxygen (O₂), nitrogen (N₂), carbon dioxide (CO₂), and other trace gases.
Percentage of O₂ in air:
The atmosphere is composed of approximately 21% oxygen. This means that for every 100 units of air, 21 units are oxygen.
Therefore, the correct answer is option C: 21%

The cartilage present in the larynx of a rabbit are:
- Thyroid cartilage: This is the largest cartilage in the larynx and forms the front and sides of the larynx. It is shaped like a shield and is commonly referred to as the Adam's apple in humans.
- Cricoid cartilage: This cartilage is located just below the thyroid cartilage and forms a complete ring. It provides support to the larynx and connects it to the trachea.
- Arytenoid cartilages: These cartilages are small and pyramid-shaped. They are located on top of the cricoid cartilage and play a crucial role in the movement of the vocal cords.
Therefore, the correct answer is D: Thyroid, cricoid, arytenoid. These three cartilages are essential for the structure and function of the larynx in rabbits.

Explanation:
The correct answer is D: The epiglottis and tongue cover the glottis. Here is a detailed explanation:
- During the process of swallowing, the food travels from the mouth to the esophagus and then to the stomach. It is important to prevent food from entering the trachea to avoid choking or aspiration pneumonia.
- The epiglottis is a flap of cartilage located at the base of the tongue. Its main function is to cover the opening of the trachea, called the glottis, during swallowing.
- When we swallow, the tongue pushes the food to the back of the mouth. As the food reaches the pharynx, the epiglottis folds back over the glottis, covering it and preventing the food from entering the trachea.
- The epiglottis acts as a protective lid, directing the food towards the esophagus instead.
- The glottis remains closed until the food passes through the pharynx and into the esophagus. Once the food has safely passed, the epiglottis returns to its normal position, allowing air to enter the trachea and lungs for normal breathing.
In summary, the epiglottis and tongue play a crucial role in preventing food from entering the trachea during swallowing. This mechanism helps ensure that food goes down the esophagus and into the stomach, while air can still enter the respiratory system without obstruction.

The statement mentioned that the O2 concentration in the tissue is almost as high as at the respiratory surface. Based on this information, we can analyze the possible outcomes:
A: Oxyhaemoglobin would not dissociate to supply O2 to the tissue
- Oxyhemoglobin is formed when hemoglobin binds with oxygen molecules at the respiratory surface.
- If the O2 concentration in the tissue is already high, there would be no need for oxyhemoglobin to dissociate and release O2 to the tissue.
B: CO2 will interfere with O2 transport
- The statement does not mention anything about CO2 interfering with O2 transport. Therefore, this option is not relevant to the given information.
C: Oxyhemoglobin would dissociate to supply O2 to the tissue
- As mentioned earlier, if the O2 concentration in the tissue is already high, there would be no need for oxyhemoglobin to dissociate and release O2 to the tissue.
D: Hemoglobin would combine with more O2 at the respiratory surface
- This option suggests that if the O2 concentration in the tissue is high, hemoglobin would combine with more O2 at the respiratory surface. However, the given information states that the O2 concentration in the tissue is almost as high as at the respiratory surface, implying that there is already sufficient O2 available at the tissue level.
Therefore, the correct answer is A: Oxyhaemoglobin would not dissociate to supply O2 to the tissue.

Explanation:
When a person has a high fever, their body temperature is elevated. This increase in body temperature can lead to faster breathing. Here's why:
1. Body's natural response: When the body temperature rises, the body tries to cool itself down. One of the ways it does this is by increasing the rate of breathing. This helps to release excess heat from the body.
2. Increased oxygen demand: The body's cells require more oxygen when the body temperature is elevated. This is because higher temperatures can increase the metabolic rate, leading to increased oxygen consumption. The increased breathing rate helps to supply more oxygen to the cells.
3. Cooling effect: Rapid breathing also helps to increase the evaporation of moisture from the respiratory tract, which can have a cooling effect on the body.
4. Stress response: In some cases, the mental worry or anxiety associated with having a high fever can also contribute to faster breathing. This is because stress can trigger the body's "fight or flight" response, which includes an increase in breathing rate.
Overall, the faster breathing seen in a person with a high fever is primarily due to the body's natural response to the elevated temperature and the increased oxygen demand of the cells.

Cilia of trachea transfer:
The cilia of the trachea are specialized hair-like structures that line the respiratory tract. They play a crucial role in maintaining the health of the respiratory system by performing various functions. In this context, the cilia of the trachea are involved in the transfer of substances. Here's a detailed explanation of each option:
A: Air into pharynx
- The cilia of the trachea help in the movement of air by creating a wave-like motion.
- This motion, known as ciliary action, moves the air in the trachea towards the pharynx, which is the upper part of the throat.
B: Air into larynx
- The larynx is the structure that contains the vocal cords and is located below the pharynx.
- The cilia of the trachea do not directly transfer air into the larynx. Their main function is to move substances within the trachea, not beyond it.
C: Mucous into lungs
- The trachea is lined with mucus-producing cells that secrete a sticky substance called mucus.
- The cilia of the trachea work in coordination with the mucus to trap and remove foreign particles, such as dust, bacteria, and viruses.
- The ciliary action moves the mucus, along with the trapped particles, upward towards the pharynx.
D: Mucous into pharynx
- This is the correct answer. The cilia of the trachea transfer the mucus, along with the trapped particles, into the pharynx.
- From the pharynx, the mucus can be swallowed or expelled through coughing, allowing the respiratory system to get rid of any harmful substances.
In summary, the cilia of the trachea transfer the mucous, along with trapped particles, into the pharynx. They do not directly transfer air into the pharynx or larynx. Their main function is to move substances within the trachea, aiding in the clearance of foreign particles from the respiratory system.

Ratio of oxyhaemoglobin and haemoglobin in the blood is based upon O2 tension:
- Oxyhaemoglobin is formed when oxygen binds with haemoglobin in red blood cells.
- The ratio of oxyhaemoglobin to haemoglobin in the blood depends on the partial pressure or tension of oxygen (O2) in the blood.
- When the O2 tension is high, more oxygen molecules bind to haemoglobin, resulting in a higher ratio of oxyhaemoglobin to haemoglobin.
- Conversely, when the O2 tension is low, oxygen molecules dissociate from haemoglobin, leading to a lower ratio of oxyhaemoglobin to haemoglobin.
Therefore, the correct answer is D: O2 tension. The ratio of oxyhaemoglobin and haemoglobin in the blood is primarily determined by the O2 tension, indicating the amount of oxygen bound to haemoglobin.

Transport of O₂ and CO₂ in the blood:
- O₂ is primarily transported in the blood by binding to hemoglobin molecules inside red blood cells, forming oxyhemoglobin. This process is known as oxygenation.
- CO₂ is transported in the blood in three main forms:
1. Dissolved CO₂: A small amount of CO₂ dissolves directly in the plasma.
2. Carbaminohemoglobin: Some CO₂ binds to hemoglobin molecules, forming carbaminohemoglobin.
3. Bicarbonate ions (HCO₃^-): The majority of CO₂ is converted into bicarbonate ions in a reaction catalyzed by the enzyme carbonic anhydrase.
- The transport of O₂ and CO₂ in the blood is essential for gas exchange between the lungs and body tissues.
- The pH of the blood plays a crucial role in maintaining the balance between acidity and alkalinity.
- In a normal man, the blood is slightly alkaline with a pH range of 7.35-7.45.
- The slight alkalinity of the blood helps in maintaining the proper functioning of enzymes and physiological processes.
- If the blood becomes too acidic or too alkaline, it can disrupt various bodily functions and lead to health issues.
- Therefore, in a normal man, the blood is slightly alkaline, indicating a proper transport of O₂ and CO₂.

Answer:
The normal shape of the diaphragm is dome-like.
Explanation:
The diaphragm is a dome-shaped muscle that separates the chest cavity from the abdominal cavity. It plays a crucial role in the process of breathing by contracting and relaxing.
The diaphragm is attached to the lower ribs, sternum, and spinal vertebrae, forming a dome-like shape. When it contracts, it flattens out and moves downward, increasing the volume of the chest cavity. This allows the lungs to expand and fill with air.
Here is a detailed explanation of the normal shape of the diaphragm:
1. Dome-like shape: The diaphragm has a convex or dome-like shape at rest. This shape allows it to effectively separate the chest and abdominal cavities.
2. Location: The diaphragm is located just below the lungs and above the abdominal organs. It is the primary muscle involved in the process of breathing.
3. Muscle fibers: The diaphragm consists of muscle fibers that contract and relax to facilitate breathing. When it contracts, it moves downward, increasing the space in the chest cavity.
4. Role in breathing: During inhalation, the diaphragm contracts and moves downward, creating a negative pressure in the chest cavity. This allows air to rush into the lungs. During exhalation, the diaphragm relaxes and moves upward, pushing air out of the lungs.
5. Shape variations: While the normal shape of the diaphragm is dome-like, it can undergo variations in shape due to certain conditions such as diaphragmatic hernia or paralysis. These conditions can cause the diaphragm to flatten or become distorted.
In conclusion, the normal shape of the diaphragm is dome-like, which allows it to effectively separate the chest and abdominal cavities and facilitate the process of breathing.

Largest Cartilage in the form of a broad ring incomplete posteriorly
The largest cartilage in the form of a broad ring that is incomplete posteriorly is the Cricoid cartilage.
Explanation:
The cricoid cartilage is a ring-shaped cartilage located at the lower part of the larynx, or voice box. It is situated just below the thyroid cartilage, commonly known as the Adam's apple. Here is a detailed explanation of each option:
A. Thyroid: The thyroid cartilage is the largest cartilage in the larynx, but it is not a complete ring. It is shaped like a shield and does not encircle the larynx completely. Therefore, it is not the correct answer.
B. Cartilage of Santorini: The cartilage of Santorini, also known as the corniculate cartilage, is a small cartilage located on top of each arytenoid cartilage. It is not a broad ring and is not the correct answer.
C. Cricoid: The cricoid cartilage is a complete ring-shaped cartilage that forms the base of the larynx. It is broad and incomplete posteriorly, meaning that its backside is not fully closed. This cartilage supports the vocal folds and plays a crucial role in maintaining the structure of the larynx.
D. Arytenoids: The arytenoid cartilages are two small, pyramid-shaped cartilages located at the back of the larynx. They sit on top of the cricoid cartilage and are involved in the movement of the vocal folds. However, they are not the largest cartilage and do not form a broad ring.
Therefore, the correct answer is C: Cricoid.

Bohr Effect:
The Bohr effect refers to the phenomenon in which the affinity of hemoglobin for oxygen decreases in response to an increase in carbon dioxide or a decrease in pH.
Explanation:
The Bohr effect is an important physiological mechanism that helps regulate the release of oxygen from hemoglobin to the tissues. It allows for the efficient delivery of oxygen to metabolically active tissues.
Statement Analysis:
A: Rise in PCO2 with a decrease in CO2 concentration - This statement is incorrect because a rise in PCO2 is associated with an increase in CO2 concentration, not a decrease.
B: Rise in PCO2 with an increase in O2 concentration - This statement is incorrect because the Bohr effect is specifically related to the effect of carbon dioxide, not oxygen.
C: Rise in PCO2 with an increase in pH - This statement is incorrect because the Bohr effect actually involves a decrease in pH, not an increase.
D: Rise in PCO2 with a decrease in pH - This statement is correct. The Bohr effect is characterized by an increase in the partial pressure of carbon dioxide (PCO2) and a decrease in pH, which leads to a decreased affinity of hemoglobin for oxygen and facilitates oxygen unloading at the tissues.
Conclusion:
The correct statement that defines the Bohr effect is D: Rise in PCO2 with a decrease in pH. The Bohr effect plays a crucial role in oxygen delivery and tissue metabolism.

Dead Space in Respiratory System
The amount of air that remains always trapped in the respiratory passage is called dead space. Dead space refers to the volume of air that is inspired but does not participate in gas exchange with the blood.
There are two types of dead space:
1. Anatomical dead space: This refers to the volume of air that remains in the conducting airways (nasal cavity, pharynx, larynx, trachea, bronchi, and bronchioles) and does not reach the alveoli where gas exchange occurs. It is a fixed volume and does not change significantly during normal breathing.
2. Physiological dead space: This includes both the anatomical dead space and any additional volume of air that reaches the alveoli but does not participate in gas exchange due to poor perfusion or ventilation-perfusion mismatch. Physiological dead space can increase in conditions such as pulmonary embolism, chronic obstructive pulmonary disease (COPD), or acute respiratory distress syndrome (ARDS).
To summarize, dead space in the respiratory system refers to the volume of air that remains trapped in the conducting airways and does not participate in gas exchange. It includes both anatomical and physiological components.

Exchange of gases between alveolar air and alveolar capillaries occur by diffusion.

Diffusion is the process by which molecules move from an area of higher concentration to an area of lower concentration. In the case of gas exchange in the lungs, oxygen moves from the alveolar air (higher concentration) to the alveolar capillaries (lower concentration), while carbon dioxide moves from the alveolar capillaries (higher concentration) to the alveolar air (lower concentration).

Here is a detailed explanation of how the exchange of gases occurs by diffusion:

1. Oxygen enters the alveolar air: When we inhale, oxygen-rich air enters the lungs and reaches the alveoli, which are tiny air sacs at the end of the respiratory bronchioles. The alveoli are surrounded by a network of capillaries.


2. Diffusion of oxygen: Oxygen molecules in the alveolar air have a higher concentration compared to the oxygen molecules in the alveolar capillaries. As a result, oxygen molecules diffuse across the thin walls of the alveoli and into the surrounding capillaries.


3. Oxygen binds to hemoglobin: Once inside the capillaries, oxygen molecules bind to hemoglobin, a protein present in red blood cells. This forms oxyhemoglobin, which can be transported to various tissues and organs in the body.


4. Carbon dioxide exchange: Simultaneously, carbon dioxide molecules present in the alveolar capillaries, which have a higher concentration, diffuse across the capillary walls and enter the alveolar air, which has a lower concentration of carbon dioxide.


5. Elimination of carbon dioxide: When we exhale, the carbon dioxide-rich air is expelled from the lungs, completing the process of gas exchange.

Therefore, the exchange of gases between the alveolar air and alveolar capillaries occurs by diffusion. This process ensures that oxygen is taken up by the blood for distribution to the body's tissues, and carbon dioxide, a waste product, is eliminated from the body.

Amount of air exchanged in breathing can be measured with a Spirometer.
Spirometry is a common method used to measure the amount of air exchanged during breathing. It is a diagnostic tool used to assess lung function and diagnose respiratory conditions such as asthma, chronic obstructive pulmonary disease (COPD), and pulmonary fibrosis.
How does a spirometer measure the amount of air exchanged in breathing?
A spirometer measures lung function by evaluating various parameters, including:
1. Tidal Volume: This is the amount of air inhaled and exhaled during normal breathing.
2. Inspiratory Reserve Volume: This is the additional volume of air that can be inhaled after a normal inhalation.
3. Expiratory Reserve Volume: This is the additional volume of air that can be exhaled after a normal exhalation.
4. Vital Capacity: This is the maximum amount of air that can be exhaled after a maximum inhalation.
5. Forced Vital Capacity (FVC): This is the maximum amount of air that can be forcefully exhaled after a maximum inhalation.
6. Forced Expiratory Volume in 1 second (FEV1): This is the volume of air exhaled forcefully in the first second during a forced exhalation.
Steps involved in spirometry:
1. The person being tested will breathe into a mouthpiece connected to the spirometer.
2. They will be instructed to perform various breathing maneuvers, such as deep inhalation, maximum exhalation, and forced exhalation.
3. The spirometer measures the volume and flow rate of air during these maneuvers.
4. The results are recorded and analyzed by a healthcare professional to assess lung function and diagnose any respiratory abnormalities.
Advantages of spirometry:
- Provides objective measurements of lung function.
- Helps in the diagnosis and management of respiratory conditions.
- Can be used to monitor the effectiveness of treatment and track disease progression.
- Non-invasive and relatively simple to perform.
- Widely available in medical settings.
In conclusion, a spirometer is the appropriate instrument for measuring the amount of air exchanged in breathing. It plays a crucial role in assessing lung function and diagnosing respiratory conditions.

Normal rate of breathing in man:
There are several factors that can affect an individual's breathing rate, including age, health, and physical activity. However, on average, the normal rate of breathing in adults is around 12-14 times per minute. Here is a detailed explanation:
Factors affecting breathing rate:
- Age: Infants and young children tend to have a higher breathing rate compared to adults.
- Health: Certain medical conditions, such as respiratory diseases or heart problems, can affect breathing rate.
- Physical activity: Engaging in exercise or strenuous activities can cause an increase in breathing rate.
Normal breathing rate in adults:
- The average rate of breathing in adults at rest is around 12-14 breaths per minute.
- This means that an adult takes approximately 12-14 inhalations and exhalations in one minute while at rest.
Exceptions:
- Breathing rates can vary depending on the individual's specific circumstances.
- For example, during physical activity or exercise, the breathing rate can increase significantly to meet the body's increased oxygen demand.
- Similarly, certain medical conditions or situations, such as anxiety or stress, can also cause an increase in breathing rate.
Conclusion:
- In general, the normal rate of breathing in adults is around 12-14 times per minute.
- However, individual variations and specific circumstances can cause deviations from this average rate.

Explanation:
The correct equation is A: Total capacity of lungs = Vital capacity + Residual air.
Here's a detailed explanation of each option:
A. Total capacity of lungs = Vital capacity + Residual air:
- The total capacity of lungs refers to the maximum volume of air that the lungs can hold, which includes both the vital capacity and the residual air.
- The vital capacity is the maximum volume of air that can be exhaled after a maximum inhalation.
- The residual air is the volume of air that remains in the lungs even after a maximal exhalation.
B. Vital capacity of lungs = Tidal air + Complemental air:
- The vital capacity is the maximum volume of air that can be exhaled after a maximum inhalation, but it doesn't include the complemental air.
- Tidal air refers to the volume of air that is inhaled or exhaled during normal breathing.
C. Total capacity of lungs = Tidal air + Complemental air + Supplemental air:
- This equation includes the total capacity of the lungs, but it incorrectly adds the supplemental air, which is not a recognized term in lung capacity measurements.
D. Total capacity of lungs = Vital capacity + Tidal air:
- This equation combines the total capacity of the lungs with the vital capacity and the tidal air, but it doesn't include the residual air.
Therefore, the correct equation is A: Total capacity of lungs = Vital capacity + Residual air.