The quark-lepton model and particle classification

140. know that in the standard quark-lepton model particles can be classified as:

• baryons (e.g. neutrons and protons) which are made from three quarks

• mesons (e.g. pions) which are made from a quark and an antiquark

• leptons (e.g. electrons and neutrinos) which are fundamental particles

• photons

and that the symmetry of the model predicted the top quark