Question

The most recent common ancestor of all eukaryotes probably did NOT have:

1) Nucleus
2) Mitochondria
3) Cell membrane
4) Endoplasmic reticulum

Answer 1

The most recent common ancestor of all eukaryotes likely did not have 2) mitochondria, as these organelles are thought to have evolved later through endosymbiosis with aerobic prokaryotes after key eukaryotic features had already developed. Hence, 2) is correct.

Step-by-step explanation:

The most recent common ancestor of all eukaryotes probably did NOT have mitochondria. The endosymbiotic theory suggests that mitochondria evolved when an ancestral prokaryote established endosymbiotic relationships with an aerobic prokaryote, which eventually evolved into mitochondria.

This relationship likely occurred after the development of several key eukaryotic features such as a nucleus and an endomembrane system, basing on the oldest fossil evidence of eukaryotes, which dates back to around 2 billion years ago.

While most eukaryotes today have mitochondria or remnants of them, the ancestral eukaryote from which they descended may not have had these organelles at the beginning of eukaryotic evolution.