Cell Biology

Step 1: Understanding Cell Wall in Different Organisms Cell walls are structural components found in many organisms, providing support and protection. However, certain organisms lack a cell wall at all stages of their life cycle. - Dinoflagellates: Most have a cell wall composed of cellulose plates, though some may lack it.
- Chrysophytes: They generally possess a siliceous (silica-based) cell wall.
- Slime Moulds: These have a cell wall during the spore-forming stage, though they may be absent in the vegetative phase.
- Protozoans: These are unicellular eukaryotic organisms that completely lack a cell wall in all life stages. They have a flexible plasma membrane instead.
Step 2: Identifying the Correct Answer Since protozoans never possess a cell wall at any stage of their life cycle, the correct answer is Option (4) Protozoans.

Step 3: Verifying the Options - Option (1) Dinoflagellates (Incorrect – Many have cellulose cell walls)
- Option (2) Chrysophytes (Incorrect – Have silica-based cell walls)
- Option (3) Slime moulds (Incorrect – Have cell walls during spore formation)
- Option (4) Protozoans (Correct – No cell wall at any stage)
Thus, the correct answer is (4) Protozoans.