question_answer 19)

  A protoxin is (a) a primitive toxin                                                         (b) a denatured toxin (c) toxin produced by Protozoa                                 (d) inactive toxin

Answer:

                  (d) A protoxin is an inactive toxin. The word 'pro' in protoxin signifies 'inactive form' B. thuringiensis forms protein crystal is which contain a toxic insecticidal protein(Bt toxin). Bt toxins are initially inactive protoxins but once ingested by insect, the inactive toxin, gets converted into an active form due to the alkaline pH of the gut which solubilises the crystals.