Consider statements about the small intestine: 1. Villi increase the surface area for absorption. 2. The duodenum receives bile and pancreatic juice. 3. The ileum is the first part of the small intestine. Which are correct? MCQ with Answer and Explanation

Explanation:
Pellagra, with the 3 Ds (dermatitis, diarrhea, dementia), is due to deficiency of niacin (vitamin B₃) or tryptophan. Beriberi is B₁, scurvy C, rickets D. Niacin is part of NAD and NADP.

Explanation:
The Lac operon in E. coli is a classic example of an inducible operon. It is normally 'off' (repressed) because a repressor protein binds to the operator, preventing transcription. However, when the inducer (allolactose, derived from lactose) is present, it binds to the repressor, inactivating it and allowing RNA polymerase to transcribe the genes needed for lactose metabolism.

Explanation:
The fluid mosaic model (Singer-Nicolson) depicts the cell membrane as a phospholipid bilayer with embedded proteins, carbohydrates, and cholesterol, giving it fluidity.