UCMP Glossary: U
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ultrastructure -- The detailed structure of a specimen, such as a cell, tissue, or organ, that can be observed only by electron microscopy. Also called fine structure.
unconformity -- Any interruption of the continuity of a depositional sequence.
undifferentiated -- adj. Unable to distinguish between. Undifferentiated rocks: rocks for which it is not possible to specify finer age divisions.
uniramious -- Among arthropods, uniramous refers to appendages that have only one branch. Insects, centipedes and millipedes, and their relatives are uniramous arthropods; land-living chelicerates such as scorpions, spiders,and mites are also uniramous but probably descended from ancestors with biramous appendages. Contrast with biramous.
upland -- n. (adj.) An area that is higher relative to the surrounding areas, but not mountainous; highland– syn.; lowland– ant.
uplift -- n. (v.) The process or result of raising a portion of the Earth’s crust through different tectonic mechanisms.
upwelling -- The raising of benthic nutrients to the surface waters. This occurs in regions where the flow of water brings currents of differing temperatures together, and increases productivity of the ecosystem.
