Which of the following is a characteristic of organisms in the protest kingdom?

Organisms in the protist kingdom are primarily characterized by their cellular structure and complexity. One of the defining traits is that they are typically single-celled organisms that possess a true nucleus, which places them in the domain Eukarya. This means that their genetic material is enclosed within a membrane-bound nucleus, distinguishing them from prokaryotic organisms such as bacteria, which lack a true nucleus.

Additionally, protists can vary significantly in their modes of nutrition, encompassing autotrophic forms (like algae) that can photosynthesize, as well as heterotrophic forms (like protozoa) that consume organic matter. However, the key characteristic remains their unicellular eukaryotic nature, making the choice of being single-celled with a true nucleus accurate for defining this kingdom.

In contrast, multicellular and autotrophic characteristics apply more closely to certain groups within plants (like algae) but do not encompass all protists, while a lack of cellular organization would not accurately describe protists, as they possess a degree of organizational complexity.