Consider the following points: (a) All excavates live in environments where oxygen availability is low; (b) all excavates lack mitochondria; and (c) all excavates have some mitochondrial genes. Based on this information, which of the following statements is TRUE of the excavate lineage?
A) Their ancestors were eukaryotes that existed prior to the origin of mitochondria.
B) Their ancestors had mitochondria, but the mitochondria were lost over time.
C) Their ancestors were not able to metabolize glucose.
D) Excavates are in the process of acquiring mitochondria through evolutionary adaptation.

Question

Quizplus · Accepted Answer

The presence of mitochondrial genes in excavates suggests that they are descended from ancestors with mitochondria, but the fact that modern excavates lack mitochondria indicates that they lost them over time. The low oxygen environments in which they live likely played a role in this loss, as mitochondria require oxygen to function. Option A is incorrect because excavates do have some mitochondrial genes, indicating that they are descended from organisms with mitochondria. Option C is incorrect because excavates likely use alternative pathways for glucose metabolism in the absence of mitochondria. Option D is incorrect because there is no evidence to suggest that excavates are actively evolving to re-acquire mitochondria.

Consider the Following Points: (A) All Excavates Live in Environments