Transport Systems 1 PDF

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Notes on Transport Systems Biology A Level OCR A....

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Transport Systems Why need a transport system? Single-celled organisms, such as bacteria and amoeba (below), can obtain nutrients and excrete waste simply by diffusion. Multi-cellular organisms, such as insects, fish and mammals, require a more specialized transport system. Need for Transport Systems  Large multicellular organism cannot rely on diffusion to move substances in and around the body  There are a number of reasons why transport systems are needed: o Metabolic rate o Surface area to volume ratio o Transporting molecules. E.g food, hormones, enzymes and waste products Metabolic rate  Large multicellular organisms have high metabolic rates  They require high volume of substances and produce a lot of waste  Diffusion alone would not be able to intake an expel all these substances Surface Area to Volume Ratio  In larger organisms, diffusion of substances would occur far too slowly to enable them to survive: the rate of diffusion increases with the square of the distance it has to travel.  This is not just because of its size, however: more important is an organism’s surface area to volume ratio.  Single-celled organisms have a very large surface area to volume ratio, because the diffusion path is so short....