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NCERT Class 11 Biology Chapter 17 Breathing and Exchange of Gases
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Breathing and Exchange of Gases
Chapter: 17
BIOLOGY
TEXTUAL QUESTIONS ANSWERS
Q.1. Define vital capacity. What is its significance?
Ans. VITAL CAPACITY (VC)–
(i) The maximum volume of air a person can breathe in after a forced expiration or the maximum volume of air a person can breathe out after a forced inspiration.
(ii) VC = TV + IRV + ERV
(iii) It varies from 3400 to 4800 ml
Q.2. State the volume of air remaining in the lungs after a normal breathing.
Ans. FUNCTIONAL RESIDUAL CAPACITY (FRC)-
(i) Volume of air that will remain in the lungs after a normal expiration.
(ii) FRC = RV + ERV = 1500 + 1500 = 300 mL.
Q.3. Diffusion of gases occurs in the alveolar region only and not in the other parts of respiratory system Why?
Ans. Diffusion of gases occurs in the alveolar region only and not in the other parts of respiratory system because of thin walls of alveoli with network of blood capillaries in alveolar wall.
Q.4. What are the major transport mechanisms for CO2? Explain.
Ans. CO₂ is transported in three ways–
(i) Dissolved gas -7% of CO₂ is carried in a dissolved state through plasma.
(ii) Bicarbonate -70% of CO₂ is carried as bicarbonate in plasma and RBC with the help of wlenzyme carbonic anhydrase. CO₂ + H₂O ⇔ H₂CO₃ ⇔ HCO₃ + H⁺
(iii) Carbaminohaemoglobin – 25% of CO₂ is carried by RBC as carbaminohaemoglobin. CO₂ + Hb HbCO₂
(iv) Every 100 ml of deoxygenated blood delivers 4 ml of CO₂ to the Alveoli.
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.
Ans. (ii) pO2 higher, pCO2 lesser.
Q.6. Explain the process of inspiration under normal conditions.
Ans. Inspiration
(i) It is a process by which fresh air enters the lungs.
(ii) Inspiration occurs when pressure in lungs (intra pulmonary pressure) is less than atmospheric pressure i.e. negative intra pulmonary pressure in the lungs.
(iii) It is caused by contraction of diaphragm and external intercostal muscles. This increases the thoracic volume and decreases intrapulmonary pressure.
Q.7. How is respiration regulated?
Ans. REGULATION OF RESPIRATION:
(a) Neural Regulation–
(i) Medullary Respiratory Centres – Medulla has respiratory rhythm center.
(ii) Pons Respiratory Centers – Pneumotaxic centre.
The function is primarily to limit inspiration.
(b) Chemical Regulation-
(i) Chemoreceptors are located in the carotid bodies and aortic bodies.
(ii) Chemoreceptors are sensitive to CO₂ and H⁺.
(iii) Increase in CO and H activates Chemoreceptors.
(iv) Carotid and aoric bodies send chemical signals to the respiratory centre in medulla.
Q.8. What is the effect of pCO2 on oxygen transport?
Ans. Dissociation of oxygen from haemoglobin or the oxygen dissociation curve is shifted to right with the increase in partial pressure of carbon dioxide.
Q.9. What happens to the respiratory process in a man going up a hill?
Ans. The respiratory rate increases due to decrease in the oxygen content of blood.
Q.10. What is the site of gaseous exchange in an insect?
Ans. Site of gaseous exchange in an insect is tracheae.
Q.11. Define oxygen dissociation curve. Can you suggest any reason for its sigmoidal pattern?
Ans. Oxygen – haemoglobin Dissociation curve-
(i) The relationship between the partial pressure of oxygen and percentage saturation of the haemoglobin with oxygen is shown by a curve called oxygen haemoglobin dissociation curve.
(ii) The amount of oxygen that can bind with haemoglobin is determined by partial pressure of oxygen (PO₂).
(iii) In normal conditions, the oxygen haemoglobin dissociation curve is sigmoid shaped or S shaped.
The sigmoid shape of the dissociation curve is due to binding of oxygen to haemoglobin. As the first oxygen molecule binds to haemoglobin, it increases the affinity for the second molecule of oxygen to bind. Subsequently, haemoglobin attracts more oxygen.
Q.12. Have you heard about hypoxia? Try to gather information about it, and discuss with your friends.
Ans. Hypoxia is a condition due to decreased supply of oxygen to the lungs. The different types of hypoxia are Hурохіс hypoxia, Anaemic hypoxia, Stagnant or ischemic hypoxia, Histotoxic hypoxia.
Q.13. Distinguish between:
(a) IRV and ERV.
Ans. INSPIRATORY RESERVE VOLUME (IRV):
(i) It is the extra volume of air that can be inspired by a forcible inspiration.
(ii) It is about 2500 to 3000 ml of air.
EXPIRATORY RESERVE VOLUME (ERV):
(i) It is the extra volume of air that can be expired by a forcible expiration.
(ii) It is about 1000 to 1100 ml.
(b) Inspiratory capacity and Expiratory capacity.
Ans. INSPIRATORY CAPACITY (IC):
(i) It is the total volume of air a person can inspire after a normal expiration.
(ii) ICTV + IRV
EXPIRATORY CAPACITY (EC):
(i) It is the total volume of air a person can expire after a normal inspiration.
(ii) ECTV + ERV
(c) Vital capacity and Total lung capacity.
Ans. VITAL CAPACITY (VC):
(i) The maximum volume of air a person can breathe in after a forced expiration or the maximum volume of air a person can breathe out after a forced inspiration.
(ii) VC = TV + IRV + ERV
(iii) It varies from 3400 to 4800 ml
TOTAL LUNG CAPACITY (TLC):
(i) Total volume of air in lungs and respiratory passage after a maximum inspiration.
(ii) TLC = VC + RV or RV +TV + IRV + ERV
(iii) It varies from 5000 to 6000 ml
14. What is Tidal volume? Find out the Tidal volume (approximate value) for a healthy human in an hour.
Ans. TIDAL VOLUME – It is the volume of air inspired or expired during normal respiration. Tidal Volume is about 500 ml.
