Definition and Factors Affecting Gas Exchange

Definition of gas exchange

Gas exchange is the biological process through which different gases are transported across respiratory surfaces to different parts of the body of a living organism.  This process occurs through diffusion when gases move from areas of high concentration to those of low concentration. Gas exchange is essential for facilitating different cellular, respiratory and metabolic activities in the body.

How gas exchange occurs in different organisms

For the process of gas exchange to occur, different gases must dissolve in body fluids first before being transported across the membranes and being diffused to surfaces of lower air concentration. Therefore gaseous exchange can only take place in moist environments and all exchange systems must have the required fluid.

Singular celled organisms have the fastest gaseous exchange rate. This is because air only travels through the cell membrane and this reduces the distance through which gas exchange has to occur and also increases surface area hence improving blood circulation.

However, this is not the case for complex living organisms such as human beings and fish. These groups of living creatures have more developed respiratory systems. This is because air has to travel long distances in order for gaseous exchange to take place. This requires an efficient transport system and mechanism. Additionally, the surface area to volume ratio through which gaseous exchange occurs is reduced and this makes the process complex and slower as compared to the case in singular celled organisms.

Factors that affect gas exchange

There are three main factors that affect gas exchange in both animals and plants:

• Surface area of the membrane. The larger the surface area of the membrane the higher the rate of gas exchange that takes place. There is a directly proportional relationship between surface area and gas exchange because when the surface area is large more blood and air are able to circulate hence increasing the rate of gas exchange.
• Concentration gradient. Concentration gradient is only possible when a membrane separates two surface areas with different concentration of gases. The difference is what actually facilitates the process of gas exchange because the gases are able to move from areas of high concentration to those of lower concentration.
• Thickness of the membrane. The rate of gaseous exchange process is also affected by the thickness of the membrane through which the gases have to diffuse. A thicker membrane reduces the rate at which gases diffuse from areas of higher concentration to those of lower concentration. This is an inversely proportional relationship and hence reduced thickness of a membrane can increase the speed at which gases flow.
• The distance of diffusion. The distance across which air and blood or plasma fluids have to travel to diffuse also determines the rate of gaseous exchange. In singular celled organisms gaseous exchange tends to be faster because the gases only have to diffuse through one cell membrane while in complex creatures gas exchange requires complex transportation and respiratory system because the gases are transported through a longer distance. This takes a longer period of time.

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