A2.1 Origins of cells (HL)

The question asks why a molecule that both stores information and catalyses reactions would be the best candidate for the first genetic material, which directly relates to the RNA World hypothesis.

For the first genetic material to drive abiogenesis, it needed to store heritable information (like DNA) and catalyse reactions (like proteins). No protein or DNA alone can do both; only RNA-like molecules fulfil both roles simultaneously.

The molecule described encodes sequence information and catalyses nucleotide joining — precisely the dual function that defines RNA (and ribozymes). This is why it qualifies as a candidate first genetic material.

The correct answer is 'It simultaneously carries heritable information and catalyses its own replication.' This captures both functions required for a self-sustaining, evolvable molecule on early Earth.

We need the property that uniquely qualifies an RNA-like molecule as the first genetic material — focusing on what no other candidate molecule can do alone.

'More chemically stable than DNA under high-temperature conditions' is incorrect. RNA is actually less stable than DNA due to its 2'-OH group, which makes it more susceptible to hydrolysis. Stability is not RNA's advantage.

'It can form a double helix' is a property associated primarily with DNA. While RNA can form partial duplexes, forming a double helix is not the key property that makes it the first genetic material candidate.

'Composed of deoxyribose sugars' describes DNA, not RNA. The molecule described in the question acts as both information carrier and catalyst — consistent with RNA (ribose-based), not DNA.

The remaining option — 'It simultaneously carries heritable information and catalyses its own replication' — correctly identifies the unique dual function that makes RNA the favoured candidate for the first genetic material.

The hypothesis is abiotic organic synthesis — that organic molecules (the building blocks of life) can form spontaneously from inorganic precursors under early Earth conditions, without any living organisms involved.

In the original Miller-Urey experiment (1953), the same setup produced amino acids including glycine and alanine. Re-analysis in 2008 identified over 20 amino acids, confirming that organic molecules form abiotically from the gases used.

Detecting amino acids and other organic molecules directly demonstrates that complex organic chemistry can emerge from simple inorganic gases and energy — supporting abiotic organic synthesis.

The correct answer is 'Amino acids and other simple organic molecules were detected in the condensed water.' This is the direct experimental evidence for abiotic organic synthesis.

We need to identify which experimental result would support the idea that organic molecules can form from inorganic precursors — the core claim of the Miller-Urey experiment.

'Water remained clear' would indicate no chemical change occurred, which would actually disprove the hypothesis of abiotic organic synthesis. This is the opposite of a supporting result.

'Gases recombined to form inorganic salts' would demonstrate only inorganic chemistry, not the production of organic molecules. This would not support the hypothesis of abiotic organic synthesis.

'Microorganisms were detected' would indicate contamination of the sealed system, not abiotic synthesis. The experiment is specifically designed to exclude living organisms to demonstrate that chemistry alone can produce organic molecules.

Only 'Amino acids and other simple organic molecules were detected in the condensed water' directly demonstrates that organic chemistry emerged from inorganic gases, supporting the hypothesis of abiotic organic synthesis.