biology-dictionary_11-06-2009

(ff) #1

Electron microscope (EM)
A microscope that focuses an electron beam through a specimen, resulting in resolving
power a thousandfold greater than that of a light microscope. A transmission electron
microscope (TEM) is used to study the internal structure of thin sections of cells. A scanning
electron microscope (SEM) is used to study the fine details of cell surfaces.
Electron microscopic
Of or relating to or involving an electron microscope.
Electron shell
An energy level at which an electron orbits the nucleus of an atom.
Electron transport chain
A sequence of electron-carrier molecules (membrane proteins) that shuttle electrons during
the redox reactions that release energy used to make ATP.
Electronegativity
The tendency for an atom to pull electrons toward itself.
Element
Any substance that cannot be broken down to any other substance.
Embryo
A developing stage of multicellular organisms; in humans, the stage in the development of
offspring from the first division of the zygote until body structures begin to appear; about
the ninth week of gestation.
Embryoblast
A group of cells near the embryonic axis of the blastocyst that develop into the embryo.
Embryogenesis
The development and growth of an embryo.
Embryonic germ-layers
The primary germ layers (endoderm, mesoderm, and ectoderm) are formed and organized
in their proper locations during gastrulation.
Embryo sac
The female gametophyte of angiosperms, formed from the growth and division of the
megaspore into a multicellular structure with eight haploid nuclei.
Enantiomer
One of a pair of molecules that are mirror-image isomers of each other.

Free download pdf