We use the single-component picture and the nearly-free-electron theory for describing collective excitations in the saturated Li-ammonia solution. The physical justification is discussed, and all predictions are compared with current experimental findings. The plasmon dispersion and the long-wavelength dielectric function of the solution can be explained within the homogeneous-electron-gas theory. The parameters r(s) = 7.4a(0) and epsilon(infinity) = 1.44 give a good description compared with inelastic x-ray scattering and optical data. The phonon spectrum of the solution is also examined. Within the scope of the empty core model with R(c) = 3.76a(0), the phonon dispersion at low q is reproduced. The ratio BB(free) = 1.34 is compared with 1.63 obtained from experiments.