Types of Respiratory Systems

 Well developed respiratory systems are found in higher animals. Simple organisms, like monerans, protists, fungi and some multicellular animals and plants , do not have any particular respiratory system, the gases simply diffuse through their cell or body surface. The following are the important gaseous exchange or respiratory structures found in protist and animals: body surfaces, gills, tracheae and lungs. Diffusion and Respiratory Structures Gases enter and leave the cells of an organism by diffusion. The gases , however, must first be dissolved in water before they can diffuse across cell membranes. Hence, respiratory structures must have gaseous exchange surfaces that are bathed in water or moist. Respiratory structures must also have ways of increasing the rate of gaseous diffusion. To do this, • The gaseous exchange surface must be large;

 • The barrier (I.e. the membrane) across which the gases diffuse must be thin;

 • There mist be ventilation mechanisms to maintain a big difference in the concentrations of the gas across the barrier (I.e. maintain a steep diffusion gradient); and

 • The gaseous exchange surface must be closely linked to the transport system. Note: By removing and distributing the diffusing gas, the transport system would also help to maintain a steep diffusion gradient across the gaseous exchange surface.