![]() Stationary Phase: Eventually, the population growth declines due to the depletion of available nutrients and the accumulation of waste products in culture. Log Phase: Also known as the exponential phase, this is when the metabolic activity of the cell is high, and the cell undergoes cell division to rapidly increase in number. During this phase, the cells increase in size due to the accumulation of proteins and other molecules necessary for cell division, without any increase in cell number. ![]() Lag Phase: This is the initial phase during which the cells acclimatize to the new environment. ![]() Under optimal growth conditions in a laboratory, the pattern of bacterial growth can be represented in the form of a curve called the growth curve. In nature, bacteria do not experience perfect environmental conditions for growth. Bacteria use specialized pili, called sex pili, for reproduction. These outgrowths assist the bacteria in attaching to other cells and surfaces, such as teeth, intestines, and rocks. Pili: They are short hair-like projections emerging from outside the cell.The presence of flagella, their number, and arrangement on their cell surface also forms a basis of classification in bacteria. The flagella beat in a propeller-like motion to help the bacterium move toward nutrients and light, as well as away from toxic chemicals. They can be found at either or both ends of a bacterial cell and sometimes all over its surface. Flagella: They are long hair-like structures attached to the cell surface that helps in bacterial movement.While the gas vacuoles allow bacteria to float in waters, the inorganic inclusions serve to store certain hydrolytic enzymes capable of destroying the host cell. Based on their nature, the inclusion bodies are of three types- gas vacuoles, inorganic inclusions, and food reserve. Inclusion Bodies: They are non-living structures present in the cytoplasm.Ribosomes: They are granular structures that are found scattered unevenly throughout the cytoplasm, which helps bacteria to synthesize proteins.The nucleoid is not membrane-bound but is simply an area of the cytoplasm where the strands of DNA are located. The bacterial DNA usually ranges in size from 160,000 base pairs to 12,200,000 base pairs (12.2 Mbp). Nucleoid: It is the region where the single, circular DNA of bacteria is found.This extra-chromosomal piece of DNA participates in cell division and confers the bacterial cell with properties such as antibiotic resistance and the ability to infect other cells known as pathogenicity. Along with some cellular parts and components such as nucleoid, ribosomes, and inclusion bodies, the cytoplasm of a bacterial cell also contains a circular (or sometimes linear) auxiliary DNA molecule called a plasmid. Cytoplasm: Present below the cytoplasmic membrane and distributed throughout the cell, it is a gel-like matrix mainly composed of water along with dissolved salts and minerals.The cytoplasmic membrane carries out many necessary cellular functions such as energy generation, protein secretion, cell division, and transport of nutrients across the cell. Cytoplasmic Membrane: It is a semi-permeable membrane composed of lipids and proteins that separates the inside of the cell from its external environment.Based on their staining properties and composition of cell wall, bacteria can be classified into gram-positive and gram-negative group. Cell Wall: It is a rigid covering composed of peptidoglycan, a polymer of protein and sugar molecules that provides shape and structural support to the cell.It provides the bacterial cell the ability to cause disease. Capsules are an important structural component that keeps the bacterium from drying out, also protecting them from being engulfed by larger microbes. ![]()
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