Characteristics of normal curve were studied as a basis of the growth rate for interpreting the response of phytoplankton on environmental gradients. The relationship between the growth rate and the environmental gradients is described as (수식) where w`, m, Wm, X, μ, and δ are the growth rate, the sort of environmental factors, the maximum growth rate, the values of environmental gradients, the mean value of environmental gradients and the standard deviation, respectively. The quantative relationships between the growth rate and pH, and nitrogen concentration in a batch culture of Chlorella vulgaris were, respectively, (수식) and (수식)