Final answer:
The cells of diplomonads and parabasalids have modified mitochondria, such as those seen in protozoan parasites Giardia lamblia and Trichomonas vaginalis.
Step-by-step explanation:
The cells with modified mitochondria include those of diplomonads and parabasalids. Modified mitochondria have occurred in certain protozoans where conventional mitochondria are absent; instead they contain organelles such as hydrogenosomes or mitosomes. This suggests that these species once had, but then lost, mitochondria, perhaps adapting to anaerobic environments. An example of protozoan parasites with unusual mitochondria-related organelles includes Giardia lamblia and Trichomonas vaginalis, which are diplomonads and parabasalids, respectively.