If all unicellular organisms were grouped into a single kingdom, what problems would arise?
If all unicellular organisms were grouped into a single kingdom, it would ignore fundamental differences in their cellular organisation. For instance, an Amoeba has a true nucleus (membrane-bound), whereas bacteria do not. Placing them together ignores that they are very different at a cellular level.
Such a grouping would create confusion because it would incorrectly combine prokaryotic and eukaryotic organisms. While Amoeba and Paramecium are unicellular and heterotrophic, they cannot be grouped with bacteria just because they are single-celled.
Therefore, classification based solely on being unicellular fails to reflect vast structural differences, necessitating separate kingdoms like Monera and Protista.
Explanation
The textbook context explains that early classification systems created confusion about where to place unicellular organisms like Amoeba, Paramecium, and bacteria. As microscopes improved, scientists realized that despite both being unicellular, Amoeba has a true nucleus (eukaryotic) while bacteria do not (prokaryotic). Grouping them into a single kingdom based solely on their unicellular nature would ignore this fundamental cellular difference, leading to incorrect scientific classification. This is why bacteria were separated into the kingdom Monera and unicellular eukaryotes were placed in Protista.