Bacterial cell structure — eukaryotic analog of the (artifact) mesosome Classical electron micrographs once described “mesosomes” in bacteria (now considered artifacts of chemical fixation). Which eukaryotic organelle was historically viewed as functionally analogous to the purported respiratory role of mesosomes?

Introduction / Context:
Early electron microscopy of bacteria revealed membrane invaginations termed “mesosomes,” thought to be involved in respiration, cell wall synthesis, or DNA segregation. Later work showed these structures were artifacts of preparation. Nonetheless, historically, mesosomes were compared to eukaryotic organelles based on presumed function.

Given Data / Assumptions:

• The question references the historical analogy grounded in respiratory function.
• Bacterial aerobic respiration occurs on the cytoplasmic membrane.
• In eukaryotes, oxidative phosphorylation occurs in mitochondria.

Concept / Approach:
If mesosomes were thought to compartmentalize respiratory enzymes in bacteria, the closest eukaryotic analogy would be mitochondria, which house the electron transport chain and ATP synthase. Golgi and lysosomes handle protein processing/trafficking and degradation, not primary ATP generation. Modern consensus emphasizes that “mesosomes” are not genuine organelles, but the analogy question still maps to mitochondria by function.

Step-by-Step Solution:
Identify the presumed function: respiration/energy generation.Match to the eukaryotic organelle with that function: mitochondria.Exclude Golgi (secretion/processing) and lysosomes (degradation).Answer with mitochondria as the historical analog.

Verification / Alternative check:
Textbook sidebars discuss the artifact status of mesosomes, noting their erstwhile comparison to mitochondria owing to respiratory enzyme localization.

Why Other Options Are Wrong:

• Golgi apparatus: involved in post-translational modification and sorting.
• Lysosomes: catabolic organelles with hydrolases, not oxidative phosphorylation.
• Peroxisomes: fatty acid oxidation and detoxification; not the main site of ATP generation.
• None of these: incorrect because mitochondria fit the historical analogy.

Common Pitfalls:
Assuming mesosomes are real functional organelles; they are artifacts, but the exam item focuses on the traditional analogy.

Final Answer:
Mitochondria