How do spirochetes and spirilla differ?
a) spirilla have an external flagella but spirochetes have axial filaments.
b) spirochetes do not have a cell wall but spirilla do.
c) spirochetes and spirilla are basically the same organisms and the terms can be used interchangeably.
d) spirilla are found in chains of cells whereas spirochetes exist as individual cells.
e) spirochetes have a rigid, corkscrew shape while spirilla are helical and more flexible.

The correct answer is option A

Spirillia have an external flagella while the spirochetes enclose their flagella in the periplasm which is a small space between the outer and inner membrane, Thus , spirochetes uses axial  filaments as locomotory organs

a "theory" a suggestion that is not 100 % accurate, or a figure. some people say its a theory because they of all the passed theory's about one subject. it depends sometimes theory might be accurate and sometimes they are.