Which cell structures show that protozoans are eukaryotes?

Protozoans are classified as eukaryotes because their cells possess complex, membrane-bound structures that are absent in prokaryotic organisms. Key cellular features that demonstrate their eukaryotic nature include:12

• True Nucleus: Unlike prokaryotes, protozoans contain a clearly defined nucleus bounded by a double-membrane envelope. This structure houses the organism's genetic material, organized into chromosomes.34
• Membrane-Bound Organelles: Protozoan cells contain specialized internal compartments, such as the endoplasmic reticulum and the Golgi apparatus, which facilitate complex cellular processes like protein synthesis and transport.32
• Mitochondria: Most protozoans possess mitochondria, which serve as the sites for cellular respiration. These organelles are enclosed by a double membrane, a hallmark of eukaryotic complexity.34
• Cytoskeleton: Protozoans utilize a sophisticated cytoskeleton composed of structural proteins, including microtubules and actin filaments, which support movement and internal organization.3

Additionally, structures such as cilia and flagella in protozoans are sheathed in the plasma membrane, a feature that distinguishes them from the simpler, non-membrane-bound flagella found in bacteria.3