Question

Monocercomonoides are a genus of single-celled organisms that live as parasites in the guts of small animals. They lack mitochondria, but other evidence shows them to be most closely related to members of the excavates. Looking at the tree for eukaryotes, what can you conclude about the Monocercomonoides?
A. Since excavates are eukaryotes, it is extremely unusual for one of them to lack mitochondria.
B. Excavates branched off before the evolution of mitochondria, so the absence is not surprising.
C. Since they are parasites of animals, they should be placed within the opisthokont branch of the tree.
D. A phylogenetic tree reflects evolutionary relationships, so they should be placed within the excavates.
E. Their lineage likely had mitochondria but lost them at some point.

Answer 1

Answer: A. Excavates branched off before the evolution of mitochondria, so the absence is not surprising.

C. Since they are parasites of animals, they should be placed within the opisthokont branch of the tree.

E. Their lineage likely had mitochondria but lost them at some point.

Explanation:

Based on the information given, the conclusion that can be made about the monocercomonoides include:

• Excavates branched off before the evolution of mitochondria, so the absence is not surprising.

• Since they are parasites of animals, they should be placed within the opisthokont branch of the tree.

• Their lineage likely had mitochondria but lost them at some point.