CBSE Questions for Class 11 Medical Biology Breathing And Exchange Of Gases Quiz 4 - MCQExams.com

• Alveoli are the primary sites of exchange of gases. 
• Oxygen and carbon dioxide are exchanged in these sites by simple diffusion mainly based on pressure/concentration gradient. 
• Solubility of the gases as well as the thickness of the membranes involved in diffusion are also important factors that can affect the rate of diffusion. 
• The diffusion membrane is made up of three major layers namely, the thin squamous epithelium of alveoli, the endothelium of alveolar capillaries and the basement substance in between them. 

• Pulmonary ventilation is a measure of the rate of ventilation, referring to the total exchange of air between the lungs and the ambient air. In a normal adult, it is about 6.0 liters per minute.
  
• Alveolar ventilation is a fraction of the pulmonary ventilation, it is the amount of air that reaches the alveoli and is available for gaseous exchange with the blood. In a normal adult, it is about  4.2 liters per minute. 
• So, the correct answer is option B.

• In a normal and healthy person, the haemoglobin is approximately 15gms per 100ml of blood. The capacity of 1gm of Hb is to combine with 1.34ml of oxygen. 
• Thus, on an average, 100ml of blood carries about 19.4ml of oxygen. It is called oxygen capacity of Hb. 
• When blood reaches the tissues, its oxygen concentration is reduced to 14.4ml, which is then collected by the venules and veins. Thus under normal conditions, approximately 5ml of oxygen is transported to tissues by 100ml of blood.
• While under strenuous conditions or during exercise, the muscle cells needs more oxygen, this demand of the muscle cells is fulfilled by the oxygen which is left unused in the human blood. 
• During exercises the partial pressure of $${O_{2}}$$ in the tissue falls, as a result of which, the oxygen concentration of blood at the tissue level is reduced to 4.4ml of oxygen/100ml of blood. 
• Thus, approximately 15ml of oxygen is transported to tissues by 100ml of blood during muscular exercise.

• Alveoli are the primary sites of exchange of gases such as oxygen and carbon dioxide by simple diffusion mainly based on pressure/concentration gradient. 
• The solubility of gasses, as well as the thickness of membranes involved in diffusion, are also some important factors, that can affect the rate of diffusion.
• Reactivity of gases does not affect the rate of alveolar diffusion as oxygen and carbon dioxide do not react in the alveoli. 

• The left lung is divided into two lobes, an upper and a lower, by the oblique fissure, which extends from the coastal to the mediastinal surface of the lung both above and below the hilum.
•  The left lung, unlike the right, does not have a middle lobe, though it does have a homologous feature, a projection of the upper lobe termed the "lingula". 
• Its name means "little tongue". Hence, the Lingula structure originates from the Superior side of the left lung.
  

• Oxygen-haemoglobin dissociation curve explains the relation between the percentage saturation of haemoglobin and partial pressure of oxygen.
• In the tissues where low pO$$_2$$, high pCO$$_2$$, high H+ concentration (low pH) and higher temperature exists, the conditions are favourable for dissociation of oxygen from oxyhaemoglobin. 
• Under these conditions, the oxygen dissociation curve shifts away from the Y-axis to the right. Hence, A decrease in pH shifts the oxygen dissociation curve to the right. 
• A right shift indicates decreased oxygen affinity of haemoglobin allowing more oxygen to be available to the tissues.
  
• Peripheral chemoreceptors in carotid and aortic bodies detect changes in blood levels of oxygen and carbon dixode & hydrogen ions.
  

• Gas exchange between the air within the alveoli and the pulmonary capillaries occurs by diffusion. 
• The oxygen must first dissolve before passing through the respiratory epithelium. 
• Gas moves from a region of high partial pressure to a region of low partial pressure, down a partial pressure gradient.

• The lowest part of pharynx is the laryngopharynx. It has two apertures, the anterior slit is 'glottis', through which it opens into the larynx and the posterior slit is 'gullet', which leads to the oesophagus.
• Thus, larynx opens into the pharynx by glottis. The glottis bear a leaf-like a cartilaginous flap, called the 'epiglottis'. Epiglottis cover the glottis during swallowing, to prevent the entry of food into it.
  Hence, the correct answer is B.

Solution:

• Correct answer is option D.

• Explanation for the correct option.

• The trachea is a straight tube extending up to the mid-thoracic cavity, which divides at the level of the 5th thoracic vertebra into a right and left primary bronchi.
• The trachea is supported by a series of cartilaginous rings that prevent it from collapsing.