What is the simple meaning of a constitutive promoter?

Correct answer: Gene can be expressed continuously

The direct answer is A: a constitutive promoter allows a gene to be expressed continuously or routinely, according to the system’s conditions. A promoter is a DNA control region where transcription machinery begins making RNA. In a constitutive arrangement, the promoter is generally active rather than requiring a special inducer. Reasoning step by step: the promoter is present before the gene; transcription machinery can bind it; RNA is produced repeatedly; the RNA can guide protein production. The exact level may vary with host, growth conditions and promoter strength, so “continuously” means ongoing expression, not necessarily unlimited expression at exactly the same level. Option A is correct. Option B is the opposite: a promoter that never permits expression would be inactive or defective, not constitutive. Option C is wrong because DNA cutting is performed by nucleases or restriction enzymes, not by the meaning of a promoter. Option D is biologically meaningless; a host does not become water. Constitutive expression can be useful, but a toxic gene may harm the host when expressed all the time, so inducible control may be safer. Exam cue: constitutive means “always on” in the ordinary regulatory sense.