A student claims that the lac operon is an example of a mechanism that an organism uses to conserve energy. Evaluate the validity of the student's claim. The claim is invalid because the lac operon requires a bacterial cell to produce extra regulatory proteins and regulatory segments of DNA. The claim is valid because the lac operon allows a bacterial cell to shut down a metabolic pathway if it is not immediately needed. The claim is valid because the lac operon allows a bacterial cell to maintain constant levels of enzymes even when they are not immediately needed. The claim is invalid because the lac operon requires a bacterial cell to constantly produce the lac repressor protein even when lactose is not present.

The claim is valid because the lac operon allows a bacterial cell to shut down a metabolic pathway if it is not immediately needed.

Explanation:

The lac operon is a cluster of genes which contain the same promoter sequence and are transcribed as a single messenger RNA (mRNA). This operon is inducible because the presence of lactose in the cell influences its transcription. Lactose can bind to the repressor of this operon, leading to a conformation change in the repressor, thereby preventing the repressor from binding to the operator and thus allowing transcription of the structural genes. After lactose addition, the β- galactosidase enzyme can break this carbohydrate into glucose and galactose, thereby there is no lactose able to bind with the repressor and therefore this operon shuts down. During transcription, the promoter of the lac operon binds both RNA polymerase and catabolite activator protein (CAP) and cyclic AMP (cAMP) complex.

desert perennials often survive by remaining dormant during dry periods of the year, then springing to life when water becomes available. most annual desert plants germinate only after heavy seasonal rain, then complete their reproductive cycle very quickly.