Which type of pathogens are one-celled organisms that have a more complex structure than bacteria

Viruses, bacteria, protozoans, fungi, and parasites differ in the following ways; viruses are among the smallest known infectious agents; bacteria are single-celled prokaryotic organisms that reproduce very quickly; protozoans are single-celled Eukaryota organisms that are generally much larger than bacteria.

Stimulants speed up the central nervous system.