Q.Students were observing a film on Paramoecium. It underwent a process of reproduction. Teacher said it is due to cell division. But students objected and said that there was no disappearnce of nuclear membrane and no spindle formation, how can it be cell division? Can you clarify?

Step 1. Note the students' objection. The students correctly recall that mitosis specifically involves disappearance of the nuclear membrane and formation of a spindle apparatus — and Paramoecium's reproduction shows neither.

Step 2. Recall the alternative type of division. The chapter describes a separate, simpler type of division called amitosis (direct division), used by unicellular organisms among others. In amitosis, the nucleus itself simply elongates and develops a constriction that deepens and splits it into two daughter nuclei, followed by division of the cytoplasm — without ever needing the nuclear membrane to disappear or a spindle to form.

Step 3. Apply this to Paramoecium. Paramoecium is a unicellular organism, and amitosis is specifically described as occurring in unicellular organisms. So the absence of nuclear-membrane disappearance and spindle formation is not a sign that no cell division occurred — it is exactly what is expected for amitotic (direct) division rather than mitotic division. …

Distinguishing amitosis from mitosis by which structural events (nuclear membrane breakdown, sp …

• Assuming 'cell division' always implies mitosis, and concluding wrongly that no division occurred because mitotic features are absent. …