9 The trp operon is regulated by a(n)activator and inducerrepressor and inducerC) activator and co-repressord) repressor and co-repressor

The trp operon is regulated by a repressor and co-repressor. So, the correct answer is d) repressor and co-repressor.

Here's a step-by-step explanation:

1. The trp operon is a group of genes that are used, or transcribed, together — that code for the components for production of tryptophan.

2. The trp repressor is a protein that binds to the operator of the trp operon and inhibits transcription of the operon — it blocks the RNA polymerase.

3. When tryptophan is plentiful, it binds to the trp repressor, which changes shape to bind even more tightly to the operator, blocking transcription.

4. When tryptophan is absent, the repressor does not bind to the operator and the genes are transcribed.

5. So, the trp operon is regulated by the presence or absence of tryptophan, which acts as a co-repressor. When tryptophan is present, it enhances the ability of the repressor to bind to the operator, thereby preventing transcription.