# Explain how the abiotic synthesis of organic monomers could have occurred on the early Earth, and outline the significance of polymerisation in the transition from chemistry to biology.

> IB DP Biology Higher Level (2023 syllabus) — A2.1 Origins of cells · Explain · 4 marks

> The early Earth, approximately 3.8–4 billion years ago, had an atmosphere very different from today's, lacking free oxygen and rich in reducing gases such as methane, ammonia, hydrogen and water vapour.

## Mark scheme (4 marks)

1. Energy sources (e.g. lightning, UV radiation, or heat from volcanic activity) provided the energy needed to drive synthesis of organic molecules from inorganic precursors.
2. Organic monomers such as amino acids, nucleotides, or simple sugars were synthesised abiotically from inorganic molecules under these conditions, as demonstrated by the Miller–Urey experiment.
3. Polymerisation joins monomers into polymers (e.g. polypeptides or polynucleotides), which can store information or carry out catalysis — functions essential for living systems.
4. Polymerisation represents the transition from simple chemistry to biology because self-replicating or catalytic polymers could undergo natural selection, allowing heredity and evolution to begin.

## Key terms

- [abiotic synthesis](https://www.gradenine.co.uk/glossary/abiotic-synthesis)
- [organic monomers](https://www.gradenine.co.uk/glossary/organic-monomers)
- [polymerisation](https://www.gradenine.co.uk/glossary/polymerisation)

## Related

- [Revision notes for IB DP Biology Higher Level (2023 syllabus)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-how-the-abiotic-synthesis-of-358d63ea) · Published by Druglandscape Ltd.