Two common strategies for acquisition of iron by terrestrial plants, fungi and bacteria are the excretion of siderophores and the reduction of organic iron-complexes at the cell surface. We investigate the feasibility of these strategies for single phytoplankton cells in a marine environment, where diffusion plays a much larger role. Using numerical models we determine the efficiency of both mechanisms, where efficiency is defined as the ratio between the increase in iron uptake rates and the excretion rate of either siderophores or electrons required to obtain this increase. This allows an estimation of the physiological cost of either mechanism. Based on our results we discuss how the maximum possible efficiency depends on the chemical kinetics of iron coordination reactions, on the biological kinetics of iron uptake, and on other parameters.