Final answer:
In the kingdom classification system, a single-celled organism with a membrane-bound nucleus, organelles, and a cellulose cell wall belongs to the kingdom Plantae (A).
Step-by-step explanation:
A single-celled organism with a membrane-bound nucleus, organelles, a cell membrane, and a cell wall composed of cellulose is classified in the biological kingdom of Plantae (A). Organisms in this kingdom are known to have cells with these characteristics. This classification is in accordance with the five-kingdom system which includes Plantae, Animalia, Fungi, Protista, and Prokaryotes. Plant cells are unique in having cell walls made of cellulose, a feature that distinguishes them from other eukaryotic cells like those found in animals and fungi, which do not have cellulose cell walls, or protists, which can have varied types of cell walls.