Biology Chapter 27 Vocabulary

peptidoglycan

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

Gram stain

A staining method that distinguishes between two different kinds of bacterial cell walls; may be used to help determine medical response to an infection.

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. Gram-positive 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. Gram-negative 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 a bryophyte (moss, liverwort, or hornwort).

endospores

Thick-coated, resistant cells produced by some bacterial cells when they are exposed to harsh conditions.

fimbriae

Short, hairlike appendages of a prokaryotic cell that help 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 called a sex pilus or conjugation pilus.

taxis

An oriented movement toward or away from a stimulus.

transduction

A process in which phages (viruses) carry bacterial DNA from one bacterial cell to another. When these two cells are members of different species, transduction results in horizontal gene transfer; A series of steps linking a mechanical, chemical, or electrical stimulus to a specific cellular response.

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, conjugation results in horizontal gene transfer. (2) In ciliates, a sexual process in which two cells exchange haploid micronuclei but do not reproduce.

F plasmid

The plasmid form of the F factor.

R plasmids

Bacterial plasmids carrying genes that confer resistance to certain antibiotics.

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.

Obligate aerobes

Organisms that require oxygen for cellular respiration and cannot live without it.

aanaerobic 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 nitrogento ammonia. Biological nitrogen fixation is carried out by certain prokaryotic organisms, some of which have mutualistic relationships with plants.

heterocysts

Specialized cells that engage in nitrogen fixation in some filamentous cyanobacteria; also called a heterocyte.

biofilm

A surface-coating colony of one or more species of unicellular organisms that engage in metabolic cooperation; most known biofilms are formed by prokaryotes.

extremophiles

Organisms that live in environmental conditions so extreme that few other species can survive there. Extremophiles include extreme halophiles (“salt lovers”) and extreme thermophiles (“heat lovers”).

Extreme halophiles

Organisms that live in a highly saline environment, such as the Great Salt Lake or the Dead Sea.

Extreme thermophiles

Organisms that thrive in hot environments (often 60 to 80 degrees C or hotter).

methanogens

Organisms that produce methane as a waste product of the way they obtain energy. All known methanogens are in domain Archaea.

decomposers

Organisms that absorb nutrients from nonliving organic material such as corpses, fallen plant material, and the wastes of living organisms and convert them to inorganic forms; also called detritivores.

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 symbiotic relationship, living in or on the host.

mutualism

A positive-positive ecological interaction that benefits individuals of both interacting species.

commensalism

A positive-neutral ecological interaction that benefits the individuals of one species but neither harms nor helps the individuals of the other species.

parasitism

A positive-negative ecological interaction in which one organism, 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.

parasite

An organism that feeds on the cell contents, tissues, or body fluids of another species (the host) while in or on the host organism. Parasites harm but usually do not kill their host.

pathogens

Organisms or viruses that cause disease.

Exotoxins

Toxic proteins that are secreted by a prokaryote or other pathogen and that produce specific symptoms, even if the pathogen is no longer present.

Endotoxins

Toxic components of the outer membrane of certain gram-negative bacteria that are released only when the bacteria die.