breathing and exchange of gases class 11 notes:-
Introduction
Gases are exchanged by simple diffusion mainly based on pressure or concentration gradient. It is the pressure contributed or exerted by an individual gas in a mixture of gases. Partial pressure for exchange is represented as pO2 and for CO2 it is pCO2 . The diffusion of gases takes place from a region of their higher partial pressure to a region of their lower partial pressure.
Factors that affect the rate of diffusion:-
The rate of diffusion, which is the process by which molecules move from an area of higher concentration to an area of lower concentration, can be influenced by several factors:
Solubility of gases:- A gas having high solubility, diffuses at a faster rate than the gas having lower solubility. For example, solubility of CO2 is 20-25 times higher than that of O2 the amount of CO2 that diffuses across diffusion membrane is much higher than that of O2.
Partial pressure:- We know that gases diffuse downhill according to their partial pressure. For example, O2 diffuses from atmospheric air having partial pressure 159 mm Hg to the alveoli where pO2 is less, i.e.,104 mm Hg.
Thickness of membrane:- More the thickness of membrane, less will be the of diffusion. Thinner the membrane, higher will be the rate of diffusion. For efficient diffusion to occur, membrane should be very thin..
Temperature: Higher temperatures increase the kinetic energy of molecules, causing them to move faster and diffuse more rapidly..
Molecular Size: Smaller molecules diffuse faster than larger ones because they can move more easily through pores and gaps in the medium.
Medium of Diffusion: Diffusion occurs more quickly in gases than in liquids, and more quickly in liquids than in solids, due to the differences in particle mobility in each state.
Distance: The shorter the distance over which diffusion occurs, the faster the process. Longer distances slow down the rate of diffusion..
Viscosity of the Medium: Higher viscosity (thicker fluid) slows down the rate of diffusion as it creates more resistance to the movement of molecules.
9. Nature of the Diffusing Substance: The chemical properties of the diffusing substance, such as polarity and charge, can affect its diffusion rate, particularly across membranes
breathing and exchange of gases class 11 notes
1. Exchange of gases between Alveoli and blood:-
Diffusion membrane:- The wall of alveoli is very thin and has rich network of blood capillaries. Due to this network, alveoli wall looks like a sheet of flowing blood and is called diffusion or respiratory or alveolar-capillary membrane. This membrane is made up of three layers:
(i) Thin squamous epithelium of elveoli that lines it.
(ii) Endothelial lining of alveolar capillaries that surround it
(iii) Basement substance :- In between thin squamous epithelium of alveoli and endothelium of alveolar capillaries, basement substance is present.
All these three layers make the total thickness of diffusion membrane nuch less than a millimeter.
Table:- Partial pressures (in mm Hg) of Oxygen and Carbon dioxide at different parts involved in diffusion in comparison to those in atmosphere.
Respiratory Gas | Atmospheric Air | Alveoli | Blood (Deoxygenated) | Blood (Oxygenated) | Tissues |
O2 | 159 | 104 | 40 | 95 | 40 |
CO2 | 0.3 | 40 | 45 | 40 | 45 |
The pO2 in the atmospheric air is higher, e 159 mm Hg than in the alveoli, i.e 104 mm Hg and pO2 in alveoli is higher than that in the deoxygenated blood in the capillaries of the pulmonary arteries (40 mm Hg).As we know, gases diffuse from their higher partial pressure to their lower partial pressure.
Therefore, O2 moves from atmospheric air to alveoli and then finally to blood, whereas the CO2 movement occurs in opposite direction. pCO2 is higher in deoxygenated blood (45 mm Hg) than that in alveoli (40 mm Hg) and it is further lower in atmospheric air, i.e 0.3 mm Hg. Therefore, CO2 moves from deoxygenated blood to alveoli and finally to the atmospheric air.
2. Exchange of Gases between Blood and Tissues:–
Gases like O2 and CO2 are exchange from blood capillaries to body cells and from body cells to blood capillaries, respectively .The pO2 is higher in systemic arteries carrying oxygenated blood, i.e., 95 mm Hg than that in tissues or body cells, i.e., 40 mm Hg.
Therefore, O2 moves from systemic arteries to body cells where it is utilized for catabolic reactions during which CO2 H2 O and energy are produced. As CO2 is produced in body cells, the pCO2 increase within the body cells, i.e., 45 mm Hg than that in the blood capillaries, i.e., 40 mm Hg.
Therefore, CO2 moves from body cells to the capillary blood through tissue fluid. Now, the blood becomes deoxygenated which is carried to the heart and hence to the lungs via pulmonary artery
Breathing supplies oxygen to the body and removes carbon dioxide, a waste product of metabolism.
Gas exchange occurs in the alveoli, where oxygen diffuses into the blood and carbon dioxide diffuses out.
Oxygen is crucial for cellular respiration, which produces energy for cellular activities.