Paper: A Study of Bacteria

A variety of classification systems are used to order bacteria. Bacteria are described as prokaryotes, organisms whose cells lack nuclei, to distinguish them from eukaryotes, organisms such as fungi, plants, and animals, whose cells contain nuclei. Because of this fundamental difference, bacteria are placed in their own kingdom, Kingdom Monera, also called Kingdom Prokaryotae. Recent molecular studies have found that a small group of organisms now known as the archaebacteria, formerly classified with bacteria because they lack a nucleus, actually have significant differences in the composition of their cell wall, plasma membrane, and other key molecular features. These structural differences have led some scientist to favor a classification scheme that groups all eukaryotes in Eukarya. Bacteria are often classified on the basis of their physical shapes. Bacteria can be spherical (cocci), rod-shaped (bacilli), or corkscrew-shaped (spirochetes). Another classification system divides bacteria into gram-negative or gram-positive according to the composition of their cell walls, a distinction identified by a staining technique called the gram stain. Scientists also classify bacteria according to whether or not they require oxygen to survive. Bacteria that require oxygen are called aerobic bacteria, or aerobes. Bacteria that lives without oxygen are called anaerobic bacteria, or anaerobes. Bacteria are also classified by their methods of obtaining carbon and energy. Carbon is the element needed to build the complex molecules required for life, and energy is required to carry out all life activities. Some bacteria are autotrophs, organisms that obtain carbon from carbon dioxide. Autotrophs derive energy from different sources. Photoautotrophs, represented by the cyanobacteria light energy are converted to the chemical energy of glucose. Chemoautotrophs, including the soil bacteria nitrobacteria, derive their energy from inorganic compounds such as hydrogen sulfide and use the energy to power the cells activities. The remaining bacteria are heterotrophs, organisms that obtain carbon by ingesting organic molecules released from decaying organisms or by preying on other bacteria, Photoheterotrophs gain energy from light, and chemoheterotrophs obtain energy from organic molecules. *Bibliography** ...