Membrane Essay Example For Students

Membrane Essay The membrane has a double lipid layer through which fat- soluble substances willmove, by passive transport or diffusion. The molecules will only move through ifthey are small enough. There are globular protein regions, which arehydrophilic. These regions allow water and water soluble substances through, butonly if they are small enough, for example starch grains are too big. Thesesubstances move through by passive transport or diffusion. Diffusion is thepassive movement of substances from a high concentration to a low concentration( N.B., you dont need a membrane present, e.g. diffusion occurs in the air). InCONTRAST, diffusion of water across a semi- permeable membrane is calledOSMOSIS. Active Transport Active transport requires energy from ATP, andinvolves carrier molecules studding the membranes. The carrier combines with themolecule on the outside, which requires ATP. It then moves across, (which alsorequires ATP), and returns. An example is glucose being transported by activetra nsport by insulin. Why is it called the Fluid Mosaic Model? Fluid- it iscalled a fluid because proteins are said to wander through the membrane (hencefluid) Mosaic- it is a mosaic because it is a collection (or mosaic) ofstructures Model- because no matter how real the diagram looks, it is not real. Therefore, it is a model. SO you put all three bits together and you get. Biology