Sentence:  As <WSD>cells</WSD> coalesced into organisms , they built new `` unnatural '' and internally controlled environments to cope even more successfully with the entropy increasing properties of the external world . 
Meaning of the word marked with <WSD> tags:  (biology) the basic structural and functional unit of all organisms; they may exist as independent units of life (as in monads) or may form colonies or tissues as in higher plants and animals