Question

Why do some biologists describe the mitochondria of diplomonads and parabasalids as “highly reduced”?

Short answer

Biologists use the phrase ‘highly reduced’ to describe the mitochondria of the protist members: diplomonads and parabasalids because the electron transport chain is missing, so these organisms respire anaerobically.

Step-by-step solution

Excavate 

In the domain Eukaryote, there are four distinct kingdoms which are further grouped into smaller branches. Excavate refers to the supergroup present in the Kingdom Protists and is characterized by the presence of an excavated grooved structure on the body. This groove was meant to facilitate feeding.

Members of the Excavate group

The supergroup Excavate is classified into three sub-groups, namely the parabasalids, euglenozoans, and diplomonads. Scientific studies on their genome have revealed that all three groups are of the monophyletic type.

Structure of diplomonads and parabasalids

The advancement in scientific studies revealed that the organisms of the diplomonad and parabasalid groupslack the presence of plastids, and the mitochondrial structure also has reduced functioning.

The mitochondria in both these groups do not contain the protein complexes of the electron transport chain and thus, are not able to respire aerobically. Due to this reason, their mitochondria are described as “highly reduced” by some biologists.