The article presents a quantitative model of the dependence of the morphological structure of the continuous culture of microalgae on external lighting and species-specific parameters. The modeling is based on the concept of two main phases that make up the cell life cycle - interphase and division phase. The interphase is considered as a light dependant process during which cell biomass increases. The division phase is independent of light and occurs when the cell reaches a certain mass equal (or higher) to the sum of masses of daughter cells. The division stage ends with cytokinesis - a complete cell division into daughter cells. The age state of the microalgae cell is characterized by the value of its biomass, while transitions from one state to another are characterized by its activity (growth and division). The model is represented by a system of differential equations that fully describe the dynamics of the ontogenesis process. The particular solution of the model for dynamically equilibrium growth of microalgae in culture at different intensity of light is analyzed. It is shown that in the continuous culture of microalgae, growing photolitotrophic, the specific growth rate is related to the morphological structure of the cell population by simple directly proportional equations with species-specific coefficients. These coefficients are the maximum growth rate in the interphase (at saturating light intensity) and cell division activity in the mitosis.