Читать книгу Algorithms in Bioinformatics - Paul A. Gagniuc - Страница 39

But why a discussion about the size of organisms? Mass diffusivity (diffusion coefficient) is a physical constant that impacts the way an organism can evolve. The cell volume must be balanced with the cell surface; otherwise, the exchange with the external environment becomes inefficient. This exchange consists of metabolites that must exit the cell per unit time or nutrients that must enter the cell per unit time. Multicellularity allows an organism to exceed the size limits normally imposed by diffusion. On the other hand, unicellular organisms with increased size have a decreased surface-to-volume ratio and may have difficulty in absorbing and transporting sufficient nutrients throughout the cell. As a counterbalance, unicellular eukaryotic organisms have among the most varied shapes and sizes observed in nature. Both unicellular and multicellular organisms can achieve a high surface-to-volume ratio by favoring DNA mutations that lead to a convoluted surface. For instance, to increase their surface area, choanocyte organisms can take many forms, such as C. taxifolia, which resembles a kind of “pine leaf” or S. fragilissima, which has a convoluted surface.