In many experimental ecological studies on phytoplankton species the growth response of an organism to the prevailing environmental conditions have been studied. Curves relating specific growth rate ~) to the external nutrient concentration (5) have been constructed to compare nutrient-limited growth of different species under steady state conditions. Microorganisms adapt their physiology to a certain limitation in order to optimize growth. Therefore the shape of the #IS curve is closely related to the way a microorganism adapts its physiology. To see how physiological adaptation and growth rate are interconnected to each other, both can be related to the internal concentration of the growth-limiting nutrient. How the growth rate is related to the internal nutrient concentration is presented in a mathematical equation.
Many phytoplankton species during growth under different nutrient limitations show a linear relationship between/t and the reciprocal value of the internal nutrient content (= Yield). This was originally observed by Droop. The model presented here gives a theoretical explanation of this phenomenon.