Chapter 24 Vocabulary

Prokaryotes

an organism that has a prokaryotic cell; an informal term for an organism in either domain Bacteria or domain Archaea

Protocells

an abiotic precursor of a living cell that had a membrane-like structure and that maintained an internal chemistry different from that of its surroundings

Ribozymes

an RNA molecule that functions as an enzyme, such as an intron that catalyzes its own removal during RNA splicing

Peptidoglycan

a type of polymer in bacterial cell walls consisting of modified sugars cross-linked by short polypeptides

Gram-Positive

describing the group of bacteria that have a cell wall that is structurally less complex and contains more peptidoglycan than the cell wall of gram-negative bacteria; bacteria are usually less toxic than gram-negative bacteria

Gram-Negative

describing the group of bacteria that have a cell wall that is structurally more complex and contains less peptidoglycan than the cell wall of gram-positive bacteria; bacteria are often more toxic than gram-positive bacteria

Capsule

1- in many prokaryotes, a dense and well-defined layer of polysaccharide or protein that surrounds the cell wall and is sticky, protecting the cell and enabling it to adhere to substrates or other cells

2- the sporangium of bryophyte (moss, liverwort, or hornwort)

Endospores

a thick-coated, resistant cell produced by some bacterial cells when they are exposed to harsh conditions

Fimbriae

a short, hairlike appendage of a prokaryotic cell that helps it adhere to the substrate or to other cells

Pili

in bacteria, a structure that links one cell to another at the start of conjugation; also known as a sex or conjugation

Taxis

an oriented movement toward or away from a stimulus

Photoautotroph

an organism that harnesses light energy to drive the synthesis of organic compounds from carbon dioxide

Chemoautotroph

an organism that obtains energy by oxidizing inorganic substances and needs only carbon dioxide as a carbon source

Photoheterotroph

an organism that uses light to generate ATP but must obtain carbon in organic form

Chemoheterotroph

an organism that requires organic molecules for both energy and carbon

Anaerobic Respiration

a catabolic pathway in which inorganic molecules other than oxygen accept electrons at the “downhill” end of electron transport chains

Nitrogen Fixation

the conversion of atmospheric nitrogen (N²) to ammonia (NH₃); biological nitrogen fixation is carried out by certain prokaryotes, some of which have mutualistic relationships with plants

Heterocysts (Heterocyte)

a specialized cell that engages in nitrogen fixation in some filamentous cyanobacteria

Biofilms

a surface-coating colony of one or more species of prokaryotes that engage in metabolic cooperation

Conjugation

1- in prokaryotes, the direct transfer of DNA between two cells that are temporarily joined; when the two cells are members of different species, results in horizontal gene transfer

2- in ciliates, a sexual process in which two cells exchange haploid micronuclei but do not reproduce

R Plasmids

a bacterial plasmid carrying genes that confer resistance to certain antibiotics

Extremophiles

an organism that lives in environmental conditions so extreme that few other species can survive there; include extreme halophiles (salt lovers) and extreme thermophiles (heat lovers)

Extreme Halophiles

an organism that lives in a highly saline environment, such as the Great Sea Lake or the Dead Sea

Extreme Thermophiles

an organism that thrives in hot environments

Methanogens

an organism that produces methane as a waste product of the way it obtains energy; in domain Archaea

Decomposers

an organism that absorbs nutrients from nonliving organic material such as corpses, fallen plant material, and the wastes of living organisms and converts them to inorganic forms; a detritivore

Symbiosis

an ecological relationship between organisms of two different species that live together in direct and intimate contact

Host

the larger participant in a symbiotic relationship, often providing a home and food source for the smaller symbiont

Symbiont

the smaller participant in a relationship, living in or on the host

Commensalism

ecological interaction that benefits the individuals of one species but neither harms nor helps the individuals of other species

Parasitism

ecological interaction in which one organisms, the parasite, benefits by feeding upon another organism, the host, which is harmed; some parasites live within the host (feeding on its tissues), while others feed on the host’s external surface

Pathogens

an organism or virus that causes disease

Exotoxins

a toxic protein that is secreted by a prokaryote or other pathogen and that produces specific symptoms, even if the pathogen is no longer present

Endotoxins

a toxic component of the outer membrane of certain gram-negative bacteria that is released only when the bacteria die

Bioremediation

the use of organisms to detoxify and restore polluted and degraded ecosystems