📌Definition Table

Term	Definition
Protocell	A membrane-bound structure thought to be a precursor to modern cells.
RNA World Hypothesis	Theory that self-replicating RNA was the first genetic material.
Compartmentalisation	Separation of internal chemistry from the environment via membranes.
Metabolism-First Model	Hypothesis that life began with metabolic networks before genetic material.
Gene-First Model	Hypothesis that self-replicating genetic molecules appeared before metabolism.
Abiogenesis	The origin of living organisms from non-living matter.

📌Introduction

The evolution of cells marks the transition from non-living chemistry to living systems capable of growth, reproduction, and metabolism. This process involved the development of self-replicating molecules, the formation of protective membranes, and the emergence of the first prokaryotic cells. While several hypotheses exist, evidence points to RNA as playing a key early role in life’s origin.

📌 Stages in the Origin of Cells

• Abiotic synthesis of organic molecules (amino acids, nucleotides) in early Earth conditions.
• Polymerisation into macromolecules such as proteins and nucleic acids.
• Self-replication: first genetic material likely RNA due to its dual role as information carrier and catalyst.
• Compartmentalisation: formation of membranes/vesicles to protect and concentrate reactions.
• Development of metabolic pathways to harness energy and resources.
• Transition from protocells to the Last Universal Common Ancestor (LUCA).

🧠 Examiner Tip: Always mention compartmentalisation as a key step — many students forget it and lose marks in origin-of-life questions.

📌 RNA World Hypothesis

• RNA can store genetic information and act as an enzyme (ribozyme).
• This dual role supports the idea that RNA preceded DNA and proteins.
• RNA ribozymes could catalyse their own replication in early life.
• DNA likely evolved later for greater stability in information storage.
• Proteins took over most catalytic functions due to greater versatility.
• Lab experiments have shown that short RNA sequences can self-replicate under certain conditions.

📌 Compartmentalisation and Protocells

• Fatty acids can spontaneously form vesicles in water.
• Vesicles can encapsulate RNA, proteins, and other molecules.
• This separation from the environment allows controlled internal chemistry.
• Vesicles can grow and divide without complex machinery.
• Early membranes were likely more permeable than modern phospholipid bilayers.
• Protocells could have formed naturally in volcanic pools or oceanic hydrothermal vents.

⚗️ IA Tips & Guidance: Simple lipid vesicle experiments can be modelled in the lab using micelle and emulsion formation — ideal for chemistry–biology crossover IAs.

📌 Competing Hypotheses: Gene-First vs Metabolism-First

• Gene-First Model: Self-replicating molecules (RNA/DNA) appeared first, later supported by metabolism.
• Metabolism-First Model: Self-sustaining chemical cycles evolved first, creating a framework for genetic material to develop.
• Hydrothermal vents could have supported metabolism-first life by providing continuous chemical gradients.
• Both models may have operated together — early metabolic cycles could stabilise and support genetic molecules.
• Debate continues due to limited fossil and experimental evidence.

🌐 EE Focus: An EE could explore metabolism-first vs gene-first origins using modern synthetic biology studies as evidence.

📝 Paper 2: Data Response Tip: In origin-of-life questions, clearly link abiotic synthesis → polymerisation → replication → membranes in the correct sequence.