Volume increases with the cube of the cells length or

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Volume increases with the cube of the cells length or diameter, whereas surface area increase with the square. In other words, the larger the cell size, the lower the ratio of surface area to volume. Therefore cell size can only increase as long as the surface area is adequate for the passage of materials into and out of the cell. Some cells that specialize in absorption have their membranes folded inwards and outwards just to increase surface area while not increasing volume as much just to increase efficiency. Diffusion Rates of Molecules Cell size is also limited by how rapidly molecules can move around in the cell to reach sites of specific cellular activities by diffusion which is the free unassisted movement of a substance from high concentration to low concentration. The rate of diffusion decreases as molecules increase in size and this is significant for macromolecules such as proteins and nucleic acids. Eukaryotes bypass this limitation by actively transporting ions, macromolecules, and other materials by using special carrier proteins. A cell of higher organisms uses cytoplasmic streaming (or cyclosis for plant cells) which is a process that involves active movement and mixing of cytoplasmic contents rather than diffusion.
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Others have specific carriers to move materials around within the cell. In the absence of these mechanisms the size of the cell is limited by these diffusion rates of the molecules it contains. The Need for Adequate Concentrations of Reactants and Catalysts A third limitation on cell size is the need to maintain adequate concentrations of the essential compounds and enzymes needed for the various processes that cells must carry out. For a chemical reaction to occur within a cell, reactants must bind with particular enzymes. The frequency of reactions increases with higher concentrations of reactants and enzymes. Every time the three dimensions of the cell double, there is an eightfold increase in the number of molecules which hinders the cell’s synthetic capabilities. Organelles An effective solution to the concentration problem is compartmentalization of activities within specific regions of the cell. To do this, most eukaryotic cells have a variety of organelles, which are membrane-bounded compartments that are highly specialized for specific functions. Bacteria, Archae, and Eukaryotes 1) Presence or absence of a membrane-enveloped nucleus Eukaryotic cells have a true membrane bounded nucleus which includes the nucleolus which is the site of ribosome synthesis Prokaryotic cells do not have a true membrane bounded nucleus, instead it is in the nucleoid which is a particular region of cytoplasm 2) Use of internal membranes to segregate function Typical bacterial and archaeal cells contain few internal membranes and have cellular functions occurring either in cytoplasm or on plasma membrane. Exceptions: Cyanobacteria.
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