Comparing Transport Systems In Flowering Plants An

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September 1997 B io Factsheet 3. Number 7 Comparing Transport in Mammals and Plants Multi-cellular organisms need to provide every cell with oxygen, water and nutrients and to do this they need a transport system because diffusion would be too slow. The development of a transport system is therefore closely connected to an organism’s surface area:volume ratio. Organisms which have a very large surface area:volume ratio e.g. protozoans, can rely upon diffusion, but as an organism gets larger, its surface area to volume ratio decreases and this makes a specialised transport system essential. Transport can be analysed under four headings: 1. The Structure of the Transport System Transport in both plants and mammals is by a system of specialised tubes. The smallest of these tubes - capillaries - may have a lumen of 5-8µm whilst veins may have lumens of 3cms diameter. In mammals this forms a circulatory system of arteries, capillaries and veins. In flowering plants, transport is not circulatory and occurs in microscopic xylem and phloem. Both transport systems use water as the basis for transport since it is a good solvent, has a high specific heat capacity, is not too viscous and is unreactive (inert). Both animals and plants have more than one type of tissue which is specialised to make transport an efficient process. The vessels and tracheids in xylem are made up of dead, lignified cells. Phloem tubes are living, as are all the mammalian transport cells and tissues. 2. What substances are Transported? In mammals, blood forms the liquid medium of transport. Blood consists of 55% plasma and 45% cells and cell fragments. Plasma consists of water, proteins e.g. fibrinogen and inorganic ions, e.g. Na+ and Ca2+. Plasma has several functions: maintains blood pressure; transports the products of digestion - amino acids, sugars, fatty acids, minerals and vitamins to

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