Xe symbol xenon xeno- prefix different xenobiotics plural noun chemical compounds that are foreign to an organism xenon noun an inert gas, traces of which are found in the atmosphere (note: The chemical symbol is Xe; the atomic number is 54 and the atomic weight is 131.30.) xeric adjective referring to a dry environment. Compare hydric xero- prefix dry xeromorphic adjective referring to a plant which can prevent water loss from its stems during hot weather xerophilous adjective referring to a plant which lives in very dry conditions xerophyte noun a plant which is adapted to living in very dry conditions xerosere noun a succession of communities growing in very dry conditions xerothermic adjective referring to an organism which is adapted to living in very dry conditions

X-ray noun a ray with a very short wavelength, which is invisible, but can go through soft tissue and register as a photograph on a film xylem noun the tissue in a plant which transports water and dissolved minerals from the roots to the rest of the plant. Compare phloem xylophagous adjective wood-eating xylophilous adjective preferring to grow on wood yeast noun a single-celled fungus that is used in the fermentation of alcohol and in making bread yellowing noun 1. a condition where the leaves of plants turn yellow, caused by lack of Light 2. a sign of disease or of nutrient deficiency yield noun the quantity of a crop or a product produced from a plant or from an area of land O The usual yield is 8 tonnes per hectare. O The green revolution increased rice yields in parts of Asia. ■ verb to produce a quantity of a crop or a product O The rice can yield up to 2 tonnes per hectare. O

The oil deposits may yield 100000 barrels a month.

zero emission vehicle noun an electric-powered vehicle with no direct emissions from its tailpipe or fuel evaporation. Abbr ZEV

zero population growth noun a state when the numbers of births and deaths in a population are equal and so the size of the population remains the same ZEV abbr zero emission vehicle zinc noun a white metallic trace element, essential to biological life. It is used in alloys and as a protective coating for steel. (NOTE: The chemical symbol is Zn; the atomic number is 30 and the atomic weight is 65.38.)

zonal adjective referring to a zone zonation noun a pattern of changes in the structure of a community depending on moisture levels, soil type and altitude O zo-nation of seaweeds on the seashore zone noun an area of land, sea or of the atmosphere zoning noun an order by a government or local council that an area of land shall be used only for a specific type of building or for a specific purpose, e.g. agricultural, industrial, recreational or residential zoo- prefix animal zoobenthos noun the invertebrate animals that live in or on the seabed, including the intertidal zone zooecology noun the scientific study of the relationship between animals and their environment zoogeographical adjective referring to animals and geography zoogeographical region noun a large area of the world where the fauna is different from that in other areas. i> biogeo-graphical region zoological adjective referring to zoology zoologist noun a scientist who specialises in zoology zoology noun the scientific study of animals zoonosis noun a disease that a human can catch from an animal zoonotic

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