Final answer:
Inducible factors are environmental stimuli-regulated proteins that activate gene transcription as needed, such as with the lac operon. Non-inducible factors are usually at constant levels but can have their activity regulated post-expression, like with steroid hormone interactions.
Step-by-step explanation:
The difference between inducible and non-inducible factors lies in the regulation of gene expression. Inducible factors are the ones that can be regulated or 'induced' by certain environmental stimuli such as molecules or physical factors. Once these factors are present, they can initiate the transcription of genes that are often not continuously expressed, but are instead expressed only as needed. An example of an inducible system is the lac operon, which is activated in the presence of lactose to enable the bacterium to utilize this sugar.
In contrast, non-inducible factors are often constitutive, meaning they are expressed at constant levels and are not regulated by inducers; however, once expressed, their activity can sometimes be modified by other means. The example of steroid hormones demonstrates this principle as they act as modulators that enhance gene expression upon binding, and once broken down, the enhanced gene expression diminishes.
Both types of factors operate at the level of transcription, utilizing various molecules like repressors, activators, and inducers to either suppress or increase the expression of genes according to the cell's needs. The trp operon is an example of a repressible system, where the presence of tryptophan acts to suppress the expression of genes involved in its synthesis.