CAIE A Level Biology 9700 · Nucleic acids and protein synthesis
A researcher is studying two species of bacteria. Species X lives in a hot spring at 75°C, while species Y lives in a temperate lake at 20°C. The DNA of species X has a GC content of 72%, whereas species Y has only 42% GC. Explain why the high GC content in species X contributes to the thermal stability of its DNA.
6 marks, so the mark scheme is looking for about 6 separate creditworthy points. Making the same point twice in different words earns it once.
Explain means: Give the reasons or the mechanism: why or how something happens. Link each point to the next with because, so or which means. A list of facts with no links usually loses the reasoning marks.
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