measure leaf temperature, chamber air temperature, PAR (photosynthetically active radiation), and atmospheric pressure. These systems may calculate water use efficiency (A/E), stomatal conductance (gs), intrinsic water use efficiency (A/gs), and sub-stomatal concentration (Ci). Chamber and leaf temperatures are measured with a thermistor sensor. Some systems are also designed to control environmental conditions. A simple and general equation for Photosynthesis is: + + (Light Energy)→ C6H12O6+O2 'Open' systems or 'closed' systems There are two distinct types of photosynthetic system; ‘open’ or ‘closed’. This distinction refers to whether or not the atmosphere of the leaf-enclosing chamber is renewed during the measurement. In an ‘open system’, air is continuously passed through the leaf chamber to maintain in the leaf chamber at a steady concentration. The leaf to be analysed is placed in the leaf chamber. The main console supplies the chamber with air at a known rate with a known concentration of and . The air is directed over the leaf, then the and concentration of air leaving the chamber is determined. The out going air will have a lower concentration and a higher concentration than the air entering the chamber. The rate of uptake is used to assess the rate of photosynthetic carbon assimilation, while the rate of water loss is used to assess the rate of transpiration. Since intake and release both occur through the stomata, high rates of uptake are expected to coincide with high rates of transpiration. High rates of uptake and loss indicates high stomatal conductance. Because the atmosphere is renewed, 'open' systems are not seriously affected by outward gas leakage and adsorption or absorption by the materials of the system. In contrast, in a ‘closed system’, the same atmosphere is continuously measured over a period of time to establish rates of change in the parameters. The concentration in the chamber is decreased, while the concentration increases. This is less tolerant to leakage and material ad/absorption. Calculating photosynthetic rate and related parameters Calculations used in 'open system' systems; For CO2 to diffuse into the leaf, stomata must be open, which permits the outward diffusion of water vapour. Therefore, the conductance of stomata influences both photosynthetic rate (A) and transpiration (E), and the usefulness of measuring A is enhanced by the simultaneous measurement of E. The internal concentration (Ci) is also quantified, since Ci represents an indicator of the availability of the primary substrate (CO2) for A. A carbon