Abstract
The kinetics of ribulose bisphosphate carboxylase-oxygenase (Rubisco) are integrated with the stoichiometry of NADPH consumption and production in a simplified model of C$_3$ chloroplast photosynthesis. The extension to a leaf is discussed with reference to the gradient of irradiance that is always present within the leaf. The optimal arrangement of photosyntheic capacity is discussed in this context. Attention is then given to the effects of gradients of CO$_2$ concentration that sometimes occur when stomata close in a heterogeneous fashion.