mass conservation law concentration conservation law <n0:math xmlns:n0="http://www.w3.org/1998/Math/MathML"> <n2:lambda xmlns:n2="http://biomodels.net/SBO/"> <n2:bvar><n2:ci definitionURL="http://biomodels.net/SBO/#SBO:0000002">a</n2:ci></n2:bvar> <n2:bvar><n2:ci definitionURL="http://biomodels.net/SBO/#SBO:0000157">n</n2:ci></n2:bvar> <n2:bvar><n2:ci definitionURL="http://biomodels.net/SBO/#SBO:0000196">S</n2:ci></n2:bvar> <n2:apply> <n2:sum /> <n2:bvar><n2:ci> i </n2:ci></n2:bvar> <n2:lowlimit><n2:cn type="integer"> 0 </n2:cn></n2:lowlimit> <n2:uplimit><n2:ci> n </n2:ci></n2:uplimit> <n2:apply> <n2:times /> <n2:apply> <n2:selector /> <n2:ci type="vector">a</n2:ci> <n2:ci> i </n2:ci> </n2:apply> <n2:apply> <n2:selector /> <n2:ci type="vector">S</n2:ci> <n2:ci> i </n2:ci> </n2:apply> </n2:apply> </n2:apply> </n2:lambda> </n0:math> If all forms of a moiety exist in a single compartment and the size of that compartment is fixed then the Mass Conservation is also a Concentration Conservation.