LUCA is inferred from universal genetic and biochemical features shared across modern cells, representing a population ancestral to all surviving cellular lineages rather than the first life.
LUCA is the inferred last population ancestral to all living organisms, supported by the universal genetic code and genes shared across the major lineages of life.
The same codon meanings and deeply conserved systems for information processing are best explained by inheritance from common ancestors. Other early life forms may also have evolved but later became extinct through competition with LUCA and its descendants.
Separate three claims: shared molecular features support common ancestry; LUCA is the last universal common ancestor, not the first life; competing early lineages need not have surviving descendants.
A translation-related gene found in bacteria, archaea and eukaryotes is stronger LUCA evidence than a gene restricted to one modern group.
LUCA describes an inferred ancestral population, not one preserved individual, and it need not have possessed every feature of modern cells.
A2.1 is usually tested as a connected argument, not as isolated facts. A strong answer builds a chain: early Earth conditions made abiotic organic synthesis plausible; origin models require small molecules, polymers, self-replication, and membranes; experiments and models support parts of the chain; LUCA, dating, and vents provide later evidence and constraints. The highest-scoring habit is to say “supports” when evidence supports, and avoid saying “proves” when it does not.