Final answer:
Treponema pallidum, the organism that causes syphilis, is a prokaryote. Plasmodium malariae, the organism that causes malaria, is a eukaryote.
Step-by-step explanation:
Treponema pallidum is the single-celled organism that causes syphilis, an STD. This organism is shaped like a corkscrew and contains no nucleus or organelles, indicating that it is a prokaryote. In contrast, Plasmodium malariae is the single-celled organism that causes malaria. It is spherical with a nucleus and several different organelles, which classifies it as a eukaryote. Therefore, Treponema pallidum must be a prokaryote and Plasmodium malariae must be a eukaryote.