In assimilation terms, at the compensation point, the net carbon dioxide assimilation is zero. Leaves release CO2 by photorespiration and cellular respiration, but CO2 is also converted into carbohydrate by photosynthesis. Assimilation is therefore the difference in the rate of these processes. At a normal partial pressure of CO2 (0.343 hPa in 1980), there is an irradiation at which the net assimilation of CO2 is zero. For instance, in the early morning and late evenings, the compensation point may be reached as photosynthetic activity decreases and respiration increases. Therefore, the partial pressure of CO2 at the compensation point, also known as gamma, is a function of irradiation. The irradiation dependence of the compensation point is explained by the RuBP (ribulose-1,5-bisphosphate) concentration. When the acceptor RuBP is in saturated concentration, gamma is independent of irradiation. However at low irradiation, only a small fraction of the sites on RuBP carboxylase-oxygenase (RuBisCO) have the electron acceptor RuBP. This decreases the photosynthetic activity and therefore affects gamma. The intracellular concentration of CO2 affects the rates of photosynthesis and photorespiration. Higher CO2 concentrations favour photosynthesis whereas low CO2 concentrations favor photorespiration.