Which gland produces the hormone melatonin? MCQ with Answer and Explanation

Explanation:
The nucleolus is a prominent, non-membrane-bound structure within the nucleus. It is the site of active ribosomal RNA (rRNA) synthesis and the assembly of ribosomal subunits. These subunits then exit the nucleus through nuclear pores to combine in the cytoplasm and form functional ribosomes for protein synthesis.

Explanation:
Double fertilization involves one male gamete fusing with the egg cell to form a diploid zygote, and the second male gamete fusing with the two polar nuclei (central cell) to form a triploid primary endosperm nucleus. The endosperm provides nutrition to the developing embryo. This unique feature ensures efficient nutrient supply and is typical of angiosperms.

Explanation:
Enterokinase (enteropeptidase), secreted by the duodenal mucosa, is the specific activator of pancreatic trypsinogen, converting it to active trypsin. Trypsin then activates other pancreatic zymogens (chymotrypsinogen, procarboxypeptidase). This cascade ensures that potent digestive enzymes are activated only in the intestinal lumen, preventing autodigestion of the pancreas.