Question

What will happen to a cockroach if it is made to drown in water ? Which of its organs and organ systems will stop function?

Answer 1

To be pretty basic, and not going in much complex structure. They die due to drowning, owned to a well known fact:

Devoid of gills, but, they can survive by holding their cycle of breathing and "altering them", thus, surviving for a short amount of time (30-50 minutes, or so).

Because of which the system alloted for respiration, fails. Instantly killing the roach, that is 'why?', it's usability, often characterised; to get rid of them.