Final answer:
The fermionic sector of the Standard Model is determined by the classification of particles based on their spin. Fermions have half-integral spin and include particles like electrons, protons, and neutrons. Bosons have integral spin and include particles like photons.
Step-by-step explanation:
The fermionic sector of the Standard Model is the way it is due to the classification of particles based on their spin. Fermions have half-integral spin and include particles like electrons, protons, and neutrons. On the other hand, bosons have integral spin and include particles like photons. Fermions and bosons behave differently in groups due to principles like Pauli's exclusion principle that restricts the occupation of quantum-mechanical states by fermions.