Describe how positive control in prokaryotes can be altered by the external environment

The positive control is control when there is an activator present which acts as a regulatory protein so the operon and activator binds and initiates the stimulation of transcription to express the gene. In absence of this activator or regulatory protein, the operon will be inactivated.

External environmental stimuli can lead to alteration of the positive control in prokaryotes such as excess lactose in the environment. These environmental stimuli can induce transcription in prokaryotes.

In this example, if glucose is not available in the environment, the transcription of the lac operon will be induced by the presence of lactose in the environment.