Concept:Trichocysts are specialised organelles found in the cortex of Paramecium.Explanation:These tiny rod-like structures lie just beneath the cell surface.When the organism is disturbed or attacked, trichocysts discharge long, thread-like filaments.This sudden ejection acts as a defensive mechanism, repelling predators or irritants.They are not used for movement, excretion, or respiration in Paramecium.Answer:B. Defence