The gland that regulates sleep-wake cycles by secreting melatonin is the: MCQ with Answer and Explanation

Explanation:
The genetic code is read in triplets of nucleotides called codons, each specifying an amino acid. AUG is the universal start codon, which also codes for methionine. In eukaryotic genes, introns are non-coding intervening sequences that are spliced out, while exons are the coding sequences that remain in the mature mRNA. Thus, statements 1 and 2 are correct.

Explanation:
Vitamin D (cholecalciferol) is unique as it can be synthesized in the skin from 7-dehydrocholesterol in the presence of UV-B radiation. It acts as a hormone to regulate calcium and phosphate homeostasis. It must be activated in the liver and kidneys. It is also obtained from dietary sources like fatty fish, egg yolk. Deficiency causes rickets/osteomalacia.

Explanation:
The macula lutea is a yellowish spot near the center of the retina. Its central depression, the fovea centralis, is the point of sharpest vision. The fovea is packed exclusively with cone cells and lacks blood vessels and rods. This high density of cones, combined with the displacement of overlying retinal layers, allows for maximum visual acuity and color discrimination in bright light. The blind spot is the optic disc.