Why are the protozoan placed in Kingdom Protista and not in Kingdom Animalia?

Explanation

**Step-by-Step Solution:**

1. **Understanding Classification Systems**: The classification of living organisms has evolved over time. Initially, protozoans were classified under the Phylum Protozoa, which was part of the Animal Kingdom.

2. **Five Kingdom Classification**: The modern classification system proposed by R.H. Whittaker divides living organisms into five kingdoms: Monera, Protista, Fungi, Animalia, and Plantae. This system was established to better categorize organisms based on their characteristics.

3. **Characteristics of Protozoans**: Protozoans are unicellular organisms, meaning they consist of a single cell. They are also classified as eukaryotes, which means their cells contain membrane-bound organelles and a defined nucleus.

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