Applicability of many plant growth models are limited because of the input data requirements. Photosynthesis and respiration equations were developed from meteorological data that could easily be obtained. The single crop parameter required was leaf area index. These equations were developed for winter wheat from measurement of net CO2 exchange with field chambers and an infrared‐gas‐analysis system. Higher gross photosynthesis rates after jointing were attributed to sink enhancement of photosynthesis. Respiration was estimated as a photosynthesis‐dependent growth component and a temperature‐biomass dependent maintenance component. The equations predicted dry matter production that agreed favorably with observed dry matter accumulation.