Which kingdom includes organisms with a nucleus and mostly unicellular forms?

• A. Protista
• B. Animalia
• C. Plantae
• D. Fungi

Answer: (A)

Having a nucleus means the cells are eukaryotic, with membrane-bound organelles. Protista is a diverse group of eukaryotes that are mostly single-celled, though some forms can be colonial or briefly multicellular. This combination—eukaryotic cells and predominantly unicellular life—fits Protista best.

In contrast, the other kingdoms are primarily multicellular and have distinct characteristics: animals are multicellular heterotrophs without cell walls; plants are multicellular and photosynthetic with cellulose cell walls; fungi are mostly multicellular (with some unicellular exceptions like yeasts) and absorb nutrients with chitin-containing cell walls.