What is the function of trichocyst in paramecium

1. Analyze the question The question asks what trichocysts do in Paramecium, a single-celled (unicellular) organism that lives in freshwater.

2. Explain the concept Paramecium is a ciliate protozoan with several specialised structures (organelles):

• Cilia: tiny hair-like structures used for movement and for sweeping food into the oral groove.
• Contractile vacuoles: remove excess water (osmoregulation) and some wastes.
• Food vacuoles: digest food.
• Trichocysts: small, spindle-shaped, rod-like structures lying just beneath the pellicle (the outer covering). When the organism is attacked or irritated, they discharge long, sharp, thread-like filaments. These can also help anchor the organism while it feeds.

3. Step-by-step solution

• Movement is done by cilia, so A is wrong.
• Excretion is mainly by contractile vacuoles and diffusion, so C is wrong.
• Respiration occurs by diffusion of gases across the cell membrane, so D is wrong.
• Trichocysts are discharged when the Paramecium is threatened by predators or harmful stimuli, so their role is defence (and anchorage).

4. Answer The correct option is B. Defence.

5. Exam tip Link the word parts: "tricho" means hair or thread, and "cyst" means a sac. Think of trichocysts as "thread-sacs that shoot out like spears to defend." Also remember the matching pairs for Paramecium: cilia → movement, contractile vacuole → osmoregulation, trichocyst → defence.