On-Line Biology Book: GLOSSARY

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eccrine glands  Sweat glands that are linked to the sympathetic nervous system and are widely distributed over the body surface.

ecological niche  The role an organism occupies and the function it performs in an ecosystem; closely associated with feeding.

ecological time  A timescale that focuses on community events that occur on the order of tens to hundreds of years.

ecology  The study of how organisms interact with each other and their physical environment.

ecosystem  The community living in an area and its physical environment.

ecotones  Well-deÞned boundaries typical of closed communities.

ecotype  A subdivision of a species; a stage in the formation of a species such that reproductive isolation has occurred.

ectoderm  The outer layer of cells in embryonic development; gives rise to the skin, brain, and nervous system. Also, the outermost tissue layer in þatworms.

ectotherms  Animals with a variable body temperature that is determined by the environment. Examples: fish, frogs, and reptiles.

effector  In a closed system, the element that initiates an action in response to a signal from a sensor. In human systems, a muscle or gland often serves as an effector.

ejaculatory duct  In males, a short duct that connects the vas deferens from each testis to the urethra.

electron  A subatomic particle with a negative charge. Electrons circle the atom's nucleus in regions of space known as orbitals.

electron acceptor  A molecule that forms part of the electron transport system that transfers electrons ejected by chlorophyll during photosynthesis. Part of the energy carried by the electrons is transferred to ATP, part is transferred to NADPH, and part is lost in the transfer system.

electron transport 1) A series of coupled oxidation/reduction reactions where electrons are passed like hot potatoes from one membrane-bound protein/enzyme to another before being finally attached to a terminal electron acceptor (usually oxygen or NADPH). ATP is formed by this process. 2) coupled series of oxidation/reduction reactions during which ATP is generated by energy transfer as electrons move from high reducing state to lower reducing state. PICTURE 1 | PICTURE 2

electrostatic attraction  The attraction between atoms of opposite charge that holds the atoms together in ionic b