Which of the following statements about the food web is correct? MCQ with Answer and Explanation

Explanation:
Viruses are non-living outside a host; they cannot carry out metabolic processes or reproduce independently. They hijack the host cell's machinery to replicate. Thus, they are obligate intracellular parasites. The reason correctly explains the assertion.

Explanation:
In the lac operon, the 'i' gene (regulatory gene) constitutively produces a repressor protein. In the absence of lactose (the inducer), this active repressor binds specifically to the operator region of the operon. The operator overlaps with the promoter, physically blocking RNA polymerase from binding to the promoter or moving forward to transcribe the structural genes (z, y, a). When lactose is present, it binds to the repressor, inactivating it and allowing transcription.

Explanation:
Plague is caused by Yersinia pestis and transmitted to humans by the bite of infected fleas (from rodents), thus vector-borne. Common cold is airborne, typhoid is water/food-borne, tetanus enters through wounds from soil. Other vector-borne diseases include malaria (mosquito), dengue (mosquito), Lyme disease (tick).