Electron spin resonance spectroscopy was used to monitor photoinduced changes in the redox state of P700, a photoactive pigment of phctosystemL in isolated Pisum sativum chloroplasts. The kinetics of the ESR signal from P700 (ESR signal I) was recorded at different concentrations of exogenous ferredoxin. A kinetic model was developed for ferredoxin-dependent cyclic electron transport around photosystem I. A multiparticle model was built to directly describe electron transfer in multienzyme complexes and restricted diffusion of mobile carriers in individual compartments (stroma, lumen, intramembrane space) of the system. The two models were compared, and a conclusion was made that the spatial organization of the system plays a significant role in shaping the kinetics of redox transitions of P700.