Explain how vesicle formation from fatty acid membranes could have contributed to the origin of the first cells.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Early Earth conditions included the presence of simple organic molecules such as fatty acids in aqueous environments. Fatty acids can spontaneously form membranous structures when placed in water.
Model answer (4 marks)
Fatty acids are amphipathic molecules that, in water, self‑assemble into bilayer membranes forming vesicles.
These vesicles create a selectively enclosed internal space, separating the internal chemistry from the external environment.
If self‑replicating molecules such as RNA were trapped inside, the vesicle would concentrate reactants and enable proto‑metabolic reactions.
Vesicles can grow by incorporating more fatty acids and can divide, passing their contents to daughter vesicles, giving a primitive form of heredity and reproduction.
These vesicles create a selectively enclosed internal space, separating the internal chemistry from the external environment.
If self‑replicating molecules such as RNA were trapped inside, the vesicle would concentrate reactants and enable proto‑metabolic reactions.
Vesicles can grow by incorporating more fatty acids and can divide, passing their contents to daughter vesicles, giving a primitive form of heredity and reproduction.
Examiner tips
- Use the term ‘amphipathic’ and ‘self‑assembly’ for the first point. Show that vesicles provide a selective barrier. Explain how concentration of reactants inside promotes reactions. Mention growth/division as a basis for heredity.
Common mistakes
- Confusing vesicle formation with simple micelle formation. Forgetting to mention the selective barrier. Not linking vesicle division to heredity.
Mark scheme (4 marks)
- Fatty acids are amphipathic molecules that spontaneously self-assemble into vesicles (or bilayer membranes) in aqueous conditions
- Vesicle formation creates a selectively enclosed internal environment / separates internal chemistry from the external environment
- Enclosure of self-replicating molecules (e.g. RNA) within vesicles would have concentrated reactants and allowed proto-metabolic reactions to occur
- Vesicles can grow and divide, passing enclosed molecules to daughter vesicles, providing a basis for heredity / reproduction
Key terms in this question
Related
- All IB DP Biology Standard Level (2023 syllabus) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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