1、Abiogenesisearly theory that held that some organisms originated from nonliving material.Also called:autogenesis,spontaneous generation自然发生说，无生源说认为生命起源于无生命有机物的学说AbnormalhemoglobinHemoglobin molecule with a different shape due to an altered Aminoacid sequence(ultimately caused by an altered DNA base
2、sequence),such as in the inherited disease sickle-cell anemia.Abscisicacida plant hormone that promotes dormancy in perennial plants and causes rapid closure of leaf stomata when a leaf begins to wilt.Acetylcholinea chemical released at Neuromuscularjunctions that binds to receptors on the surface o
3、f the plasma membrane of muscle cells,causing an electrical impulse to be transmitted.The impulse ultimately leads to muscle contraction.AcetylCoAan intermediate compound formed during the breakdown of Glucose by adding a two-carbon fragment to a carrier molecule(Coenzyme A or CoA).Acidrainthe preci
4、pitation of sulfuric acid and other acids as rain.The acids form when sulfur dioxide and nitrogen oxides released during the combustion of Fossilfuels combine with water and oxygen in the atmosphere.Acquiredimmunodeficiencysyndrome(AIDS)a collection of disorders that develop as a result of infection by the Humanimmunodeficiencyvirus(HIV),which attacks Helpertcells,crippling the Immunesystem and greatly reducing the bodys ability to fight infection;results in premature death brought about by various diseases that overwhelm the compromised immune system.
