The transfer of nutrients from the enveloping boundary layer into and within the cells is biologically mediated, being effected principally through a series of substance-specific membrane transport systems. Modern molecular biology is providing the means to investigate both the mechanisms by which cells marshal and assemble components in cellular synthesis and how their operations are regulated. In the case of membrane transport systems, working against a concentration gradient, structure and function conform to a generalised arrangement common to most living cells. In essence, these accept specific target molecules and transfer them to the sites of deployment. These movements are generally not spontaneous and, so, require the expenditure of energy. Power, fuelled by ATP phosphor-ylation, is used to generate and maintain ion gradients and proton motive forces, through the coupling of energy-yielding reactions to energy-consuming steps (Simon, 1995).
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