Final answer:
Protozoa and algae are classified as protists under the six-kingdom classification system.
Explanation:
According to the six-kingdom classification system, the two groups of organisms classified as protists are protozoa and algae. Protists are simple, predominantly unicellular eukaryotic organisms that include various organisms like slime molds, euglenoids, algae, and protozoans. These organisms are categorized under the Protista Kingdom, known for their diversity and inclusion of single-celled forms with defined cell nuclei. Protozoa and algae fall under the Protista Kingdom, reflecting the broad range of unicellular eukaryotes encompassed within this group.
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