Inducible vs. repressible operon
Inducible and repressible operon is defined as operon response in the presence of metabolite.
Genes are turned on in the presence of metabolite (e.g. lac) is called inducible operon.
Genes are turned off in the presence of metabolite (e.g. trp) is called repressible operon.
Lac operon is inducible operon which means if lactose is present then lac operon is turned on. It states that lactose induces the gene expression.
Lac operon is expressed when lactose is present and if lactose is absent then expression is blocked. For this, repressor binds to operator and blocks transcription of the operon.
Trp operon is a repressible operon which means if tryptophan is present then trp operon is turned off. And incase of low tryptophan availability, operon is turned on.