Sentence:  Homozygous and heterozygous * * f cells , * * f and homozygous and heterozygous * * f <WSD>cells</WSD> were used to test each sample ; however , in the interest of clarity and conciseness only the results obtained with homozygous * * f and homozygous * * f cells will be presented here . 
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