  Massless Dirac electrons in graphene fill Landau levels with energies scaled
as square roots of their numbers. Coulomb interaction between electrons leads
to mixing of different Landau levels. The relative strength of this interaction
depends only on dielectric susceptibility of surrounding medium and can be
large in suspended graphene. We consider influence of Landau level mixing on
the properties of magnetoexcitons and magnetoplasmons - elementary
electron-hole excitations in graphene in quantizing magnetic field. We show
that, at small enough background dielectric screening, the mixing leads to very
essential change of magnetoexciton and magnetoplasmon dispersion laws in
comparison with the lowest Landau level approximation.
