Encyclopedia of Biology

neurotransmitter Achemical made of amino acids and peptides that switch on or off nerve impulses across the synapse between neur ...

nitrogenase AnENZYMEcomplex from bacteria that catalyzes the reduction of dinitrogen to ammonia: N 2 8e–+10H+Ô 2NH 4 + H 2 with ...

anaxon. The nodes contain voltage-sensitive sodium channels or gates that generate action potentials. The neural signal jumps fr ...

noncyclic electron flow Thefirst stage of photo- synthesis; begins when light energy enters a cluster of pigment molecules (call ...

pores. Nuclear pores are found where the inner and outer membranes are joined. The space is filled with filamentous material. Th ...

contact (dipolar) shifts, and considerable increases in the nuclear spin relaxation rates. From this type of measurement, struct ...

RNA is produced in the nucleolus of the cell and trav- els to the cytoplasm through the pores of the nuclear envelope. nucleosid ...

nucleosome A beadlike subunit of chromatin, the material chromosomes are made of, consisting of about 150–200 base pairs of DNA ...

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obligate aerobe Any organism that must utilize atmospheric oxygen in its metabolic pathways and for cellular respiration, and ca ...

ommatidium Asingle unit, or visual section, of a compound eye such as that found in insects. It resem- bles a single simple eye ...

order A taxonomic grouping between class and fami- ly. The order consists of groups that are more alike than those in a class. S ...

moves from areas of high-water/low-solute concentra- tion to areas of low-water/high-solute concentration. osmotic pressure Pres ...

ovulation The process in which a mature ovary folli- cle opens and releases an egg (secondary oocyte) enclosed in a mucouslike m ...

oxygen One of the most important elements for biological systems and for other processes, such as reacting with other substances ...

pacemaker Another name for the sinoatrial (SA) node. See alsoSA NODE. paedogenesis The ability to reproduce while still in immat ...

parasitoid Anorganism that lives in or on the body of a single host individual during its development and eventually kills the h ...

pattern formation The direction given to cells to form a specific three-dimensional structure in shaping the development of an o ...

pedigree The line of descent; a documented list or table of ancestors, as in a genealogical record of an ani- mal or person. pel ...

perception The brain’s interpretation of a sensory stimulus; conscious mental awareness. perennial Aplant that lives through man ...