Final answer:
The major difference between the three pathways of complement is how they are activated: the alternate pathway is spontaneous, the classical pathway requires the presence of an antibody, and the lectin pathway is activated by an acute-phase protein.
Step-by-step explanation:
The major difference between the three pathways of complement is how they are activated. The alternate pathway is activated spontaneously and does not require the presence of an antibody. The classical pathway is dependent on the presence of an antibody bound to an antigen, which is part of the adaptive immune response. The lectin pathway is activated when a specific acute-phase protein binds to a pathogen.