In the 'Breathing and Exchange of Gases' chapter, the functionality of oxygen and carbon dioxide have been thoroughly explained. As we all know, organisms use oxygen to indirectly break down simple molecules, such as amino acids, fatty acids, glucose, etc. and derive energy that is utilized to carry out various activities. Carbon dioxide, which is considered harmful for, both living organisms and the environment, is also let out when the above catabolic reactions occur.

Hence, in this chapter, it has been made evident that the cells require an uninterrupted supply of oxygen and the carbon dioxide that is produced by the cells needs to be sent out continuously. This process of giving and taking carbon dioxide produced by the cells and oxygen from nature respectively is called breathing, and scientifically respiration. Want to know more about the topics of this chapter, read below.

• Respiratory Organs in organisms
• Breathing Mechanics
• How are Gases Exchanged?
• How are Gases transported?
• How is respiration regulated?
• Problems of Respiratory System

The students get an insight into the mechanism of breathing from this chapter. A human's respiratory system consists of respiratory organs that assist in the breathing process. Breathing, technically termed respiration, has been defined in the chapter as an exchange process between two gases, i.e. inhale of oxygen from the atmosphere and exhale of carbon dioxide produced by the cells, from the body into the atmosphere.

The whole chapter majorly talks about the meaning, definitions, importance, and differentiation of respiration and breathing. A few other relevant topics covered under this chapter are different respiratory volumes and capacities, transport and exchange of gases, major respiratory disorders, and more.

Q1. Define vital capacity. What is its significance?
Answer: Vital capacity refers to the maximum volume of air that can be breathed in after forced expiration. It is about 3.5 to 4.5 liters in the human body.
It promotes the act of supplying fresh air and getting rid of foul air, thereby increasing the gaseous exchange between the tissues and the environment.

Q2. State the volume of air remaining in the lungs after normal breathing.
Answer: The volume of air remaining in the lungs after normal breath out is called functional residual capacity (FRC). It combines expiratory reserve volume (ERV) and residual volume (RV). ERV is the maximum volume of air that can be exhaled after a normal expiration and it is about 1000 mL to 1500 mL. RV, on the other hand, refers to the volume of air remaining in the lungs after maximum expiration and is about 1100 mL to 1500 mL.
Thus, FRC = ERV + RV 1500 + 1500 = 3000 mL
Hence, the functional residual capacity of the human lungs is about 2500 - 3000 mL.

 Q3. Diffusion of gases occurs in the alveolar region only and not in the other parts of the respiratory system. Why?
Answer: For efficient exchange of gases, the respiratory surface must have certain characteristics such as:
1. It must be thin, moist, and permeable to respiratory gases.
2. It must have a larger surface area.
3.It must be highly vascular. 
Only the functional alveolar region has these characteristics. Thus, diffusion of gases occurs in this region only.

Q4. What are the major transport mechanisms for CO₂? Explain.
Answer: The major transport mechanism for CO₂ is transported by sodium bicarbonate as well as red blood cells. See, about 70% of carbon dioxide is transported as sodium bicarbonate. As CO₂ diffuses into the blood plasma, a large part of it combines with water to form carbonic acid in the presence of the enzyme carbonic anhydrase. Carbonic anhydrase is a zinc enzyme that speeds up the formation of carbonic acid. This carbonic acid dissociates into bicarbonate (HCO₃^- ) and hydrogen ions (H⁺ ). About 20 – 25% of CO₂ is transported by the red blood cells as carbaminohaemoglobin. Carbon dioxide binds to the amino groups on the polypeptide chains of hemoglobin and forms a compound known as carbaminohaemoglobin.

Q5. What will be the pO₂ and pCO₂ in the atmospheric air compared to those in the alveolar air?
(i) lesser, higher
(ii) higher, lesser
(iii) higher, higher
(iv) lesser, lesser
Answer: PO₂ higher, pCO₂ lesser
As the partial pressure of oxygen in atmospheric air is higher than that of oxygen in alveolar air. So, in atmospheric air, pO2 is about 159 mm Hg and in alveolar air, it is about 104 mm Hg. The partial pressure of carbon dioxide in atmospheric air is lesser than that of carbon dioxide in alveolar air. In atmospheric air, pCO 2 is about 0.3 mmHg and in alveolar air, it is about 40 mm Hg.

Q6. Explain the process of inspiration under normal conditions.
Answer: Inspiration is the process, during which atmospheric air is drawn inside the body. It can occur if the pressure within the lungs (intra-pulmonary pressure) is less than the atmospheric pressure, i.e., there is a negative pressure in the lungs for atmospheric pressure.
It is initiated by the contraction of the diaphragm which increases the volume of the thoracic chamber in the anteroposterior axis. The contraction of external intercostal muscles lifts the ribs and the sternum causing an increase in the volume of the thoracic chamber in the dorso-ventral axis. The overall increase in the thoracic volume causes a similar increase in pulmonary volume. An increase in pulmonary volume decreases the intra- pulmonary pressure to less than the atmospheric pressure which forces the air from outside to move into the lungs.

Q7. How is respiration regulated?
Answer: Respiration is regulated by the respiratory center present in the brain stem. The pneumatic center and the apneustic center in the pons and medulla rhythmicity center that regulates the respiratory system. The neural signal from this center can reduce the duration of inspiration and thereby alter the respiratory rate.
A chemosensitive area is situated adjacent to the rhythm center which is highly sensitive to CO₂ and hydrogen ions. An increase in these substances can activate this center, which in turn can signal the rhythm center to make necessary adjustments in the respiratory process by which these substances can be eliminated. Receptors associated with the aortic arch and carotid artery also can recognize changes in CO 2 and H⁺ concentration and send necessary signals to the rhythm center for remedial actions. The role of oxygen in the regulation of respiratory rhythm is quite insignificant.

Q8.  What is the effect of pCO₂ on oxygen transport?
Answer: The pCO₂ (partial pressure of carbon dioxide) plays an important role in the transportation of oxygen as CO₂ shows a higher affinity to hemoglobin than that O₂. The low pCO₂ and high pO₂ favor the formation of oxyhemoglobin in the alveoli because CO₂ in atmospheric air is lesser than that of gaseous oxygen (O₂). And at the tissues, the high pCO₂ and low pO₂ favor the dissociation of oxygen from oxyhemoglobin. So, the affinity of hemoglobin for oxygen is enhanced by the decrease of pCO₂ in blood. Therefore, oxygen is transported in the blood as oxyhemoglobin and oxygen dissociate from it at the tissues.

Q9. What happens to the respiratory process in a man going up a hill?
Answer:
- When a man goes uphill, he gets less oxygen with each breath, and as we know that when altitude increases, the oxygen level in the atmosphere decreases.
- Because of the decrease in atmospheric O₂, the amount of oxygen in the blood starts to decline because of less oxygen content breathe in air.
- The respiratory rate increases in order to respond to the decrease in the oxygen content of the blood.
- Simultaneously, the rate of heartbeat increases to increase the supply of oxygen to the blood.

Q10. What is the site of gaseous exchange in an insect?
Answer: In insects, gaseous exchange takes place through a network of tubes collectively known as the tracheal system. The small openings on the sides of an insect’s body are called spiracles and oxygen-rich air enters through the spiracles. These spiracles are connected to the network of tubes. From the spiracles, oxygen enters the tracheae and from here, oxygen diffuses into the cells of the body. The circulation of carbon dioxide follows the reverse path and the CO₂ from the cells of the body first enters the tracheae and then leaves the body through the spiracles.

Q11. Define oxygen dissociation curve. Can you suggest any reason for its sigmoidal pattern?
Answer: The oxygen dissociation curve is a graph that shows the percentage of saturation of oxyhemoglobin at various partial pressures of oxygen. This curve shows the equilibrium of oxyhemoglobin and hemoglobin at various partial pressures. In the case of the lungs, the partial pressure of oxygen is high. So, hemoglobin binds to oxygen and forms oxyhemoglobin.
 

Q12. Have you heard about hypoxia? Try to gather information about it, and discuss it with your friends.
Answer: Hypoxia is a type of condition characterized by an inadequate or decreased supply of oxygen to the lungs. It is caused by several extrinsic factors such as a reduction in pO₂, inadequate oxygen, etc. It can be also classified as either generalized, affecting the whole body, or local, affecting a region of the body.
Different types of hypoxia are: Anemic hypoxia and Hypoxemic hypoxia

Q13. (a) Distinguish between IRV and ERV
Answer:

Q14.  Distinguish between inspiratory capacity and Expiratory capacity.
Answer: Difference between Inspiratory capacity and Expiratory capacity: 
Inspiratory capacity: It is the volume of air that can be inhaled after a normal expiration.
- IC = TV + IRV
Expiratory capacity: It is the volume of air that can be exhaled after a normal inspiration.
- EC = TV + ERV

Q15.  Distinguish between Vital capacity and Total lung capacity.
Answer:

Q16. What is Tidal volume? Find out the Tidal volume (approximate value) for a healthy human in an hour.
Answer: Tidal volume is the volume of air that is transported into and out of the lungs ( inspired or expired ) with each normal respiratory cycle. Tidal volume is approximately 6000 to 8000 mL of air per minute for a healthy human.
We can calculate the hourly tidal volume for a healthy human. If, Tidal volume = 6000 to 8000 mL/minute
So, the Tidal volume in an hour will be = 6000 to 8000 mL × (60 min)
= 3.6 × 10 ⁵ mL to 4.8 × 10 ⁵ mL
Hence, the hourly tidal volume for a healthy human is approximately 360000 ml-480000 ml.