Q4. Besides the lac operon, name three operons NCERT lists as examples.
Any three of the trp, ara, his and val operons (NCERT page 100).
Q5. What does the y gene’s product do, and why does the cell need it before the operon is fully on?
It is permease, which increases the cell’s permeability to β-galactosides; lactose enters the cell through its action, so a low level of it must be present for lactose to get in and induce the operon (NCERT pages 100–101).
Q6. Why is control of the lac operon by its repressor called negative regulation?
Because a regulatory protein, the repressor, switches transcription off by binding the operator; inducer relief raises expression above the low basal level, subject to other controls (NCERT pages 100–101).
Q7. Assertion: the lac repressor does not switch off the trp operon. Reason: each operon has its specific operator and specific repressor. Are both true, and does the reason explain the assertion?
The assertion is true for the normal lac/trp systems because LacI and the trp repressor have different binding specificity. NCERT’s reason is an example-specific simplification; one regulator can control more than one operon in other systems.
Q8. How does regulation of gene expression explain the development of an adult from an embryo?
The development and differentiation of the embryo into an adult result from the coordinated regulation of the expression of several sets of genes (NCERT page 100).