biology-dictionary_11-06-2009

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Stem cells
The common, self-regenerating cells in the marrow of long bones that give rise, by
differentiation and division, to red blood cells and all of the different types of white blood
cells.
Stratified squamous epithelium
A multiple-layered epithelium composed of thin, flat superficial cells and cuboidal and
columnar deeper cells
Stereoisomer
A molecule that is a mirror image of another molecule with the same molecular formula.
Stereoscopic vision
Ability to perceive a single, three-dimensional image from the simultaneous but separate
images delivered to the brain by each eye.
Sterols
Any of various alcohols having the structure of a steroid, usually with a hydroxyl group(OH)
attached to the third carbon atom. Sterols are found in the tissues of animals, plants,fungi,
and yeasts and include cholesterol.
Steroids
A class of lipids characterized by a carbon skeleton consisting of four rings with various
functional groups attached.
Sternum
A long flat bone in the front of the body, to which the collarbone and most of the ribs are
attached.
Stigma
In plants, the region of a carpel serving as a receptive surface for pollen grains, which
germinate on it.
Stilt roots
An aerial root.
Stimulus
Any internal or external change or signal that influences the activity of an organism or of
part of an organism.

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