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As organisms increase in size they have to develop strategies to enable adequate gas exchange to occur. Explain why this is and how organisms overcome this problem.

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Introduction

As organisms increase in size they have to develop strategies to enable adequate gas exchange to occur. Explain why this is and how organisms overcome this problem. (WRITE ABOUT S.A. : VOLUME RATIO GETTING SMALLER ETC.) When the volume of a gas exchange surface increases, the diffusional distance for the oxygen also increases. This causes problems because when the diffusional distance reaches a certain point, gas exchange stops being efficient and new and more efficient strategies for gas exchange are needed. Often, diffusion through the skin is not a satisfactory method of gas exchange because the skin is designed to protect the body, therefore it is a non permeable suface. ...read more.

Middle

When the organisms become too large, changes in shape are not sufficient for respiration - the organism needs more oxygen than it can take in through simple methods of diffusion through the skin (or the eqivalent). Some creatures use gills as a method for gas exchange. Some gills open directly to the environment; others, as in fishes, are enclosed in a cavity. Many invertebrates use gills as a major means of gas exchange. Almost any thin-walled extension of the body can be viewed as a gill. Gills usually have a large surface area in relation to their mass. Although gills are generally used for water breathing and lungs for air breathing, this association does sometimes vary, for example by the water lungs of sea cucumbers. ...read more.

Conclusion

In a number of fishes, the diffusional distance of water to blood is 0.0003 to 0.003 millimetre. This is about the same distance as the air to blood pathway in a mammilian lung. The countercurrent flow system is mainly related to the efficiency of gas exchange. This system is needed because in water there is only about 1% of oxygen, and diffusion is thousands of times slower than it is out of the water. Fishes need a lot of metabolic energy for swimming. Often, a fast moving fish will swim with its mouth open so that it can take in more oxygen, which can be changed into ATP. Metabolic energy is also used to pump water over the the lammelae so that they can stay supported. ...read more.

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