# Explain why the hypothesis that the first cells arose from pre-existing cells is not accepted, and outline the evidence that supports an abiotic origin of the first cells on early Earth.

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

## Mark scheme (4 marks)

1. The hypothesis that cells only arise from pre-existing cells cannot apply to the very first cells, as there were no cells on early Earth from which they could have originated.
2. Simple organic molecules (monomers such as amino acids) can form abiotically from inorganic precursors, as demonstrated by the Miller–Urey experiment using conditions simulating early Earth's atmosphere.
3. RNA is thought to have been the first self-replicating molecule (RNA world hypothesis), as RNA can both store genetic information and catalyse reactions (ribozymes), suggesting it could have driven early chemical evolution without proteins.
4. Lipids can spontaneously form bilayer vesicles (protocells/liposomes) in aqueous environments, providing a plausible mechanism by which a membrane-bound compartment capable of enclosing replicating molecules could have formed abiotically.

## Key terms

- [abiotic](https://www.gradenine.co.uk/glossary/abiotic)

## 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-why-the-hypothesis-that-the-bc4c64e3) · Published by Druglandscape Ltd.