CAIE A Level Biology 9700 · Inheritance
Explain how the presence of lactose leads to the expression of the lac structural genes in E. coli. In your answer, refer to the roles of regulatory and structural genes, and explain why the lac operon is described as an inducible system.
4 marks, so the mark scheme is looking for about 4 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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