Final answer:
A drug targeting protozoan cells is not expected to affect ribosomes, as these are similar in both protozoan and human cells, making them a challenging target for selective drug treatments.
Step-by-step explanation:
A drug that inhibits the growth of protozoan cells would not be expected to affect ribosomes among the given options. Protozoans are eukaryotic organisms and, therefore, their cells have organelles and structures similar to those of human cells, including ribosomes.
Whereas the cell wall is absent in most protozoan and animal cells, the cytoplasmic membrane and mitochondria are crucial for cell survival and energy production, making them potential targets for drugs. However, ribosomes across different eukaryotic organisms, unlike those in prokaryotes, are remarkably similar, which presents a challenge when creating selective treatments that do not also harm the human host.