E. coli cells with a mutated z gene of the lac operon cannot grow in medium containing only lactose as the source of energy because -

1. A. They cannot synthesize functional beta galactosidase
2. B. They cannot transport lactose from the medium into the cell
3. C. The lac operon is constitutively active in these cells
4. D. In the presence of glucose, E. coli cells do not utilize lactose

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