Fig. 2. Kinetics of mass-specific Na⁺ uptake rate in neonate and adult water flea Daphnia magna as a function of sodium concentration. Data are expressed as mean ± 1 s.e.m. (N=6). Kinetic parameters (Michaelis constant [K_m] and maximal velocity [V_max]) for sodium uptake in neonate and adult daphnids were determined by means of nonlinear regression analyses (one-site binding), as previously described (Bianchini and Wood, 2003).