  We study the effects of a low concentration of adatoms or single vacancies in
the linear-response transport properties of otherwise clean graphene. These
impurities were treated as localized orbitals, and for each type two cases with
distinct coupling symmetries were studied. For adatoms, we considered top- and
hollow-site adsorbates (TOP and HS). For vacancies, we studied impurity
formation by soft bond reconstruction (REC), as well as the more symmetric case
of charge accumulation in unreconstructed vacancies (VAC). Our results indicate
that the transport is determined by usual impurity scattering when the
graphene-impurity coupling does not possess $C_{3v}$ symmetry (TOP and REC). In
contrast, VAC impurities decouple from the electronic states at the Dirac
points, and yield no contribution to the resistivity for a sample in charge
neutrality. Furthermore, the inversion-symmetry-conserving HS impurities also
decouple from entire sets of momenta throughout the Brillouin zone, and do not
contribute to the resistivity within a broad range of parameters. These
behaviors are protected by $C_{3v}$ and inversion symmetry, respectively, and
persist for more general impurity models.
