Assertion (A): Xylem vessels are dead at maturity. Reason (R): Lignin deposition provides strength but blocks cytoplasm, leading to cell death. MCQ with Answer and Explanation

Explanation:
Osmotic pressure (OP) is a colligative property of a solution, meaning it depends on the number of solute particles dissolved in a given volume of solvent, not on the nature or size of the particles. It is defined as the hydrostatic pressure that must be applied to a solution to prevent the net flow of water (osmosis) into the solution across a semipermeable membrane. According to the van't Hoff equation, osmotic pressure is directly proportional to the molar concentration of solute particles and the absolute temperature. The more concentrated the solution, the higher its osmotic pressure.

Explanation:
Plasmids are small, circular, extrachromosomal DNA molecules in bacteria widely used as cloning vectors in genetic engineering. Restriction enzymes are part of the bacterial immune system, found in bacteria and archaea, not viruses, protecting them against bacteriophages. Polymerase Chain Reaction (PCR) requires a thermostable DNA polymerase (like Taq) to synthesize new DNA strands. Thus, statements 1 and 3 are correct.

Explanation:
Enterokinase (enteropeptidase) is secreted by the intestinal mucosa and activates the pancreatic proenzyme trypsinogen to trypsin, which then activates other zymogens. Pepsin is active in the stomach, renin is a milk-curdling enzyme (chymosin), carboxypeptidase is a pancreatic protease. This cascade ensures that protein-digesting enzymes are activated only in the appropriate location to prevent autodigestion.