Final answer:
Some protozoa and primitive eukaryotes lack centrosomes and centrioles. They have evolved alternative mechanisms for cellular organization and division.
Step-by-step explanation:
The organisms that lack centrosomes and centrioles are some protozoa and certain primitive eukaryotes. These organisms include some flagellates that move in a random fashion compared to other microscopic organisms with flagella. They have evolved different mechanisms for cellular organization and division, such as the MicroTubule Organizing Center (MTOC) in plant cells.