Which of the following best describes organisms in the Protista kingdom?

The Protista kingdom is characterized by a diverse range of organisms that are primarily unicellular, although some can form simple multicellular structures. Option C accurately captures this characteristic by stating that organisms in this kingdom are unicellular and can also form colonies without developing true tissue layers. This reflects the variability within the Protista, which encompasses organisms such as protozoa, algae, and slime molds, showcasing both unicellular organisms and those that exhibit more complex social structures.

The other options do not appropriately describe the Protista kingdom. For instance, multicellularity with tissue layers is more characteristic of higher kingdoms like Plantae, Animalia, and Fungi, rather than Protista. Similarly, being exclusively prokaryotic and flagellated pertains more to the domain of bacteria and archaea, not protists, which are primarily eukaryotic. Finally, while some protists are autotrophic and photosynthetic, many are heterotrophic or mixotrophic, meaning they can derive energy from various sources, making the statement about exclusive autotrophy inaccurate.