The Lac operon in E. coli is an example of an: MCQ with Answer and Explanation

Explanation:
Rana tigrina is the scientific name of the Indian bullfrog. Homo sapiens refers to humans, Felis domestica is the domestic cat, and Crocodylus palustris is the marsh crocodile. Binomial nomenclature gives each organism a unique genus and species name. Rana is the genus, tigrina the species, both italicized when printed.

Explanation:
Vitamin A (retinol) is crucial for the synthesis of rhodopsin, maintaining normal vision, especially in dim light. Vitamin D deficiency impairs calcium absorption, leading to rickets in children. Vitamin C (ascorbic acid) is a water-soluble vitamin, not fat-soluble; vitamins A, D, E, and K are fat-soluble. Thus, statements 1 and 3 are correct.

Explanation:
Retroviruses (e.g., HIV) possess two copies of single-stranded RNA and the enzyme reverse transcriptase, which transcribes the RNA into DNA upon infection. This DNA integrates into the host genome. Other viruses may have dsDNA, ssDNA, or dsRNA, but the defining feature of retroviruses is the RNA genome and reverse transcription.