![]() A typical bacterial/archaeal cell is a few micrometers in size, while a typical eukarytotic cell is about 10x larger. Keep in mind that the size difference (bacterial/archaeal cells = smaller, eukaryotic cells = larger) is on average. This also means that they evolve faster over time, giving them more opportunities to adapt to environments. So, small cells grow and reproduce faster. As the surface-to-volume ratio goes down, it indicates that the cell has less of an opportunity to bring in the nutrients needed to support the cell’s activities – activities such as growth and reproduction. Now think of the volume as representing what the cell has to support. Based on this, the larger cell would have an advantage. The larger the surface area, the more possibilities exist for engaging in these activities. Think of the cell surface as the ability of the cell to bring in nutrients and let out waste products. The surface-to-volume ratio of the smaller cell is 3, while the surface-to-volume ratio of the larger cell decreases to 1.5. Let us look at a 2 μm cell in comparison with a cell that is twice as large at 4 μm. This ratio changes as a cell increases in size. These advantages relate back to the surface-to-volume ratio of the cell, a ratio of the external cellular layer in contact with the environment compared to the liquid inside. Much of it has to do with the advantages derived from being small. There are reasons why most archaeal/bacterial cells are much smaller than eukaryotic cells. Eukaryotic microbes also tend to exhibit a wide array of shapes, particularly the ones that lack a cell wall such as the protozoa.Ĭell size, just like cell morphology, is not a trivial matter either, to a cell. There are additional shapes seen for bacteria, and an even wider array for the archaea, which have even been found as star or square shapes. Pleomorphic – pleomorphic organisms exhibit variability in their shape. ![]() Spirilla and spirochetes are differentiated by the type of motility that they exhibit, which means it is hard to separate them unless you are looking at a wet mount. There are three sub-categories: the vibrio, which are rods with a single curve and the spirilla/ spirochetes, which are rods that form spiral shapes. Curved rods – obviously this is a rod with some type of curvature.bacilli) – a bacillus is a rod-shaped cell. cocci) – a coccus is a spherically shaped cell. Bacteria tend to display the most representative cell morphologies, with the most common examples listed here: Cell morphology can be used as a characteristic to assist in identifying particular microbes but it’s important to note that cells with the same morphology are not necessarily related. The shape dictates how that cell will grow, reproduce, obtain nutrients, move, and it’s important to the cell to maintain that shape to function properly. It might seem like a trivial concept but to a cell it is not. ![]() So, to honor these differences this text will refer to the groups as the archaea, the bacteria, and the eukaryotes and try to leave the prokaryotic reference out of it.Ĭell morphology is a reference to the shape of a cell. Both cells are prokaryotic because they lack a nucleus and other organelles (such as mitochondria, Golgi apparatus, endoplasmic reticulum, etc), but they aren’t closely related genetically. More recently, microbiologists have been rebelling against the term prokaryote because it lumps both bacteria and the more recently discovered archaea in the same category. “Pro” means “before,” while “Eu” means “true,” indicating that prokaryotes lack a nucleus (“before a nucleus”) while eukaryotes have a true nucleus. The crux of their key difference can be deduced from their names: “karyose” is a Greek word meaning “nut” or “center,” a reference to the nucleus of a cell. In general, prokaryotes are smaller, simpler, with a lot less stuff, which would make eukaryotes larger, more complex, and more cluttered. They are either prokaryotic or eukaryotic. Traditionally, cellular organisms have been divided into two broad categories, based on their cell type. ![]()
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