Sentence:  The increase in <WSD>oxygen</WSD> uptake rates from 1.2 to 2.6 mg / l / hr which followed an increase in rotor speed was believed to be related to resuspension of solids which had settled at the lower rotor speeds . 
Meaning of the word marked with <WSD> tags:  a nonmetallic bivalent element that is normally a colorless odorless tasteless nonflammable diatomic gas; constitutes 21 percent of the atmosphere by volume; the most abundant element in the earth's crust