Saturday, December 27, 2008

Gasesous Exchange in Cell Division

All living organisms exchange carbon dioxide and oxygen with their environment for carrying out different functions. Organisms must exchange gases with their environment in order to carry out photosynthesis, cellular respiration, and other essential processes. This gas exchange is accomplished exclusively through passive diffusion.

Oxygen and carbon dioxide are the two most important gases that organisms exchange. Certain microorganisms are also capable of taking up nitrogen gas for the purpose of nitrogen fixation. Three primary factors govern gas exchange: the concentration gradient of the gas, the amount of surface area available for gas exchange, and the distance over which the diffusion takes place. Gas concentrations differ between air and water. The concentration of oxygen is much higher in air than in water, whereas carbon dioxide concentration is similar in both. Density differences between water and air influence the uptake of gases. Diffusion is slower in water because water is denser than air. Aquatic organisms must therefore move large quantities of water over their gas exchange surfaces to get the same amount of gas found in a much smaller volume of air. Oxygen has a higher concentration in the atmosphere than does carbon dioxide. Oxygen therefore diffuses into animals more rapidly than carbon dioxide diffuses into plants.

Organisms use different methods and organs for the purpose of gas exchange, which depends on their habitat.

Body surface

Small organisms and plants accomplish gas exchange by simple diffusion across their cell or body surfaces. Multicellular organisms, which have a large surface area relative to their body volume, exchange gases across their body surface. Earthworms, algae, etc. are examples. Body surfaces specialized for gas exchange are moist, which allows easy exchange of gases.


Larger, more complex organisms use specialized gas exchange structures such as gills and lungs. Gills provide large surface area for gas exchange. Gills are convoluted growths covered by thin epithelial layers, containing.a rich supply of blood vessels. Since gases cannot reach individual hody cells directly from these structures, large organisms use transport fluids to move gases around their bodies. The surface area devoted to gas exchange in an organism is directly proportional to the organism's size and metabolic needs. Gas exchange on land is a problem because of the water loss associated with exposing the exchange surfaces to dry air. Terrestrial gas' exchange is thus a compromise between obtaining necessary gases and avoiding water loss.

Tracheal system

This is a network of tubes present in insects. These tracheal systems open outside through openings called spiracles, through which oxygen enters into the network of tubes. Thus, there is direct exchange of gases between the cells and the tracheal tubes.


These are the structures present in the lungs. Lungs are the well-developed organ system for the effective exchange of gases between atmosphere and the blood present in the terrestrial organisms. Lungs are elastic sacs that allow the animal to pump air in and out of the body. The trachea of the lungs divide into two branches, which in turn divide into many sub-branches known as bronchioles. The bronchioles end in small, thin-walled sacs known as alveoli. The presence of alveoli increases the effective surface area for gaseous exchange. Alveoli have a rich supply of fine blood vessels with very thin walls through which gas can easily diffuse into and out.

Gas Exchange In Plants

In plants gas exchange usually takes place through stomata, small openings present on the epidermis of the leaves. The stomata open into spongy parenchyma and the gas exchange takes place between the cells and the gas filled in the air space. Gas exchange is needed for both respiration and photosynthesis. 

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