Term | Definition |
virus | Noncellular parasitic agent consisting of an outer capsid and an inner core of nucleic acid. |
capsid | Protective protein containing the genetic material of a virus. |
bacteriophage | Virus that infects bacteria. |
lytic cycle | Bacteriophage life cycle in which the virus takes over the operation of the bacterium immediately upon entering it and subsequently destroys the bacterium. |
lysogenic cycle | Bacteriophage life cycle in which the virus incorporates its DNA into that of a bacterium; occurs preliminary to the lytic cycle. |
lysogenic cell | Cell that contains a prophage (virus incorporated into DNA), which is replicated when the cell divides. |
reverse transcriptase | Viral enzyme found in retroviruses that is capable of converting their RNA genome into a DNA copy. |
emerging viruses | Newly identified viruses that are becoming more prominent, usually because they cause serious disease. |
viroid | Infectious strand of RNA devoid of a capsid and much smaller than a virus. |
prion | Infectious particle consisting of protein only and no nucleic acid. |
neurodegenerative disease | Disease, usually caused by a prion, virus, or bacterium, that damages or impairs the function of nervous tissue.prokaryote |
prokaryote | Organism that lacks the membrane-bound nucleus and the membranous organelles typical of eukaryotes. |
binary fission | Splitting of a parent cell into two daughter cells; serves as an asexual form of reproduction in bacteria. |
conjugation | Transfer of genetic material from one cell to another. |
conjugation pilus (pl., conjugation pili) | In a bacterium, elongated, hollow appendage used to transfer DNA to other cells. |
transformation | Taking up of extraneous genetic material from the environment by bacteria. |
transduction | Exchange of DNA between bacteria by means of a bacteriophage. |
Bacteria (domain Bacteria) | Are the more common type of prokaryote. |
peptidoglycan | Polysaccharide that contains short chains of amino acids; found in bacterial cell walls. |
facultative anaerobes | Are able to grow in either the presence or the absence of gaseous oxygen. |
obligate anaerobes | Are unable to grow in the presence of free oxygen. |
photoautotrophs | Organism able to synthesize organic molecules by using carbon dioxide as the carbon source and sunlight as the energy source. |
chemoautotroph | Organism able to synthesize organic molecules by using carbon dioxide as the carbon source and the oxidation of an inorganic substance (such as hydrogen sulfide) as the energy source. |
chemoheterotroph | Organism that is unable to produce its own organic molecules and therefore requires organic nutrients in its diet. |
saprotroph | Organism that secretes digestive enzymes and absorbs the resulting nutrients back across the plasma membrane. |
mutualism | Symbiotic relationship in which both species benefit in terms of growth and reproduction. |
commensalism | Symbiotic relationship in which one species is benefited, and the other is neither harmed nor benefited. |
parasitism | Symbiotic relationship in which one species (the parasite) benefits in terms of growth and reproduction to the detriment of the other species (the host). |
pathogen | Disease-causing agent, such as viruses, parasitic bacteria, fungi, and animals. |
endospore | Spore formed within a cell; certain bacteria form endospores. |
Cyanobacteria (pl., cyanobacteria) | Photosynthetic bacterium that contains chlorophyll and releases oxygen; formerly called a blue-greeen alga. |
lichen | Symbiotic relationship between certain fungi and either cyanobacteria or algae, in which the fungi possibly provide inorganic food or water and the algae or cyanobacteria provide organic food. |
Archaea (domain Archaea) | Were considered to be a unique group of bacteria. |
methanogen | Type of archaean that lives in oxygen-free habitats, such as swamps, and releases methane gas. |
halophile | Type of archaean that lives in extremely salty habitats. |
thermoacidophile | Type of archaean that lives in hot, acidic, aquatic habitats, such as hot springs or near hydrothermal vents. |