Trichocyst of Paramecium is required for

The correct option is defence.

Detailed Explanation:
1. Structure of Trichocysts:
Trichocysts are specialized, spindle-shaped secretory organelles located in the ectoplasm (the outer layer of cytoplasm) of ciliate protozoans, such as Paramecium. They lie perpendicular to the body surface and are distributed regularly beneath the pellicle.
2. Role in Defence:
When a Paramecium is subjected to injury, chemical irritation, or attacks by predators, these organelles are rapidly discharged. Upon stimulation, the trichocysts eject long, sticky, thread-like shafts tipped with a sharp spike. This sudden discharge can startle, distract, or physically repel predators, serving a vital protective function.
3. Functions of Other Processes:
• Osmoregulation: Managed by the contractile vacuoles, which pump out excess water entering the cell.
• Nutrition: Accomplished via the cytostome (cell mouth) and cytopharynx, which direct food into food vacuoles for digestion.
• Reproduction: Carried out via binary fission (asexual) and conjugation (sexual exchange of genetic material).