The light compensation point (Ic) is the light intensity on the light curve where the rate of photosynthesis exactly matches the rate of cellular respiration. At this point, the uptake of CO2 through photosynthetic pathways is equal to the respiratory release of carbon dioxide, and the uptake of O2 by respiration is equal to the photosynthetic release of oxygen. The concept of compensation points in general may be applied to other photosynthetic variables, the most important being that of CO2 concentration – CO2 compensation point (Γ). 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 given partial pressure of CO2 (0.343 hPa in 1980 atmosphere), there is an irradiation at which the net assimilation of CO2 is zero. For instance, in the early morning and late evenings, the light compensation point Ic may be reached as photosynthetic activity decreases and respiration increases. The concentration of CO2 also affects the rates of photosynthesis and photorespiration. Higher CO2 concentrations favour photosynthesis whereas low CO2 concentrations favor photorespiration, producing a CO2 compensation point Γ for a given irradiation. Light compensation point As defined above, the light compensation point Ic is when no net carbon assimilation occurs. At this point, the organism is neither consuming nor building biomass. The net gaseous exchange is also zero at this point. Ic is a practical value that can be reached during early mornings and late evenings. Respiration is relatively constant with regard to light, whereas photosynthesis depends on the intensity of sunlight. Depth For aquatic plants where the level of light at any given depth is roughly constant for most of the day, the compensation point is the depth at which light penetrating the water creates the same balanced effect. CO2 compensation point The CO2 compensation point (Γ) is the CO2 concentration at which the rate of photosynthesis exactly matches the rate of respiration. There is a significant difference in Γ between plants and plants: on land, the typical value for Γ in a plant ranges from 40–100 μmol/mol, while in plants the values are lower at 3–10 μmol/mol. Plants with a weaker CCM, such as C2 photosynthesis, may display an intermediate value at 25 μmol/mol. The μmol/mol unit may alternatively be