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Describe how size of living organisms determines the process, structure and function of gas exchange system.

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Introduction

Describe how size of living organisms determines the process, structure and function of gas exchange system Organisms rely on diffusion to fulfil their physiological needs. Over time different organisms have adapted so that they can meet their own demands. This is particularly evident in the way gaseous exchange relates to the size of the organism. The organism's oxygen requirements are proportional to its volume i.e. the bulk of the respiring tissue it contains. The exchanges are proportional to the surface area over which diffusion of oxygen can take place. The mathematical rule is - as an object increases in volume the ratio of its total surface area to voulme decreases i.e. The larger the object the smaller it's surface : volume ratio. In small organisms such as protozoa (Amoeba- around 1mm in diameter) ...read more.

Middle

In small organisms the distance is short and does not cause a problem. In larger organisms the distance is larger. This has been overcome by either developing a circulatory system with an oxygen carrying pigment, or by reducing the diffusion distance so that none of the cells are far from the surface. Various organisms have done this in various ways: * Flattened body -e.g. flatworms/leaves on plants - thus reducing the distance between surfaces * Thin tissues - e.g. Hydra - again reducing the distance of diffusion * External medium brought into body - e.g. tracheal system in insects - so that in itimate association is obtained with all tissues. As previously stated amoeba proteus possesses a large surface area to voulme ratio which satisfies its metabolic needs. Many other groups of invertabrate animals such as cnidarians (e.g. ...read more.

Conclusion

In mammals, the use of lungs is adapted. Air moves into or out of the lungs as a result of differences in pressure between atmospheric and alveolar air. When the atmospheric pressure is greater than the pressure within the lungs, air tends to flow down the pressure gradient and inspiration occurs. When the pressure in the lungs is greater than atmospheric pressure, air moves out of the lungs and into the atmosphere. These pressure changes are brought about by changes in the volume of the thorax, which in turn, are produced by contraction or relaxation of the respiratory muscles. The lungs follow these changes passively. The presence of a respiratory pigment in blood further increases the efficiency of the blood's oxygen carrying capacity. Blood that contains any form of respiratory pigment is a more efficient oxygen carrier than one without one. This is because the pigment permits far greater amounts of oxygen to be taken up and transported. ...read more.

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