Consider statements about plant biology: 1. Xylem vessels are dead at maturity. 2. Phloem sieve tubes are living at maturity. 3. Cambium is responsible for primary growth. Which are correct? MCQ with Answer and Explanation

Explanation:
Iodine deficiency impairs thyroid hormone synthesis, leading to elevated TSH and enlargement of the thyroid gland (goiter). Iodized salt prevents it.

Explanation:
The lac operon in E. coli is a classic example of an inducible operon. It is normally 'off' (repressed) because the lac repressor protein, produced by the 'i' gene, binds to the operator, preventing transcription of the structural genes (z, y, a) needed for lactose metabolism. However, when lactose is present in the environment, it is converted to allolactose, which acts as an inducer. Allolactose binds to the repressor, changing its shape and preventing it from binding to the operator, thus 'inducing' or allowing transcription to occur.

Explanation:
The Haber-Bosch process synthesizes ammonia from N₂ and H₂ under high temperature and pressure with a catalyst. It is the main industrial nitrogen fixation for fertilizers. Biological fixation is by microbes.