Viral Structure and Common Diseases — NEET Biology

Correct answer: B — S2, S3 and S5 only

This question tests the understanding of acellular organisms (viruses, viroids, prions) and lichens, which are discussed outside the five-kingdom classification system. S1: Viruses are obligate intracellular parasites and are characterized by an inert crystalline structure outside the host cell. This statement is correct. Viruses are non-cellular, obligate parasites with an inert crystalline structure outside the living cell. S2: The genetic material in viruses can be either RNA or DNA, and some complex viruses may contain both. This statement is NOT correct. A virus contains either RNA or DNA, but never both. S3: Viroids are infectious agents smaller than viruses, composed of free RNA of high molecular weight, but without a protein coat. This statement is NOT correct. Viroids are composed of free RNA of *low* molecular weight, not high molecular weight. S4: Prions are infectious proteins that cause neurodegenerative diseases such as mad cow disease in cattle and Creutzfeldt–Jacob disease in humans. This statement is correct. Prions are abnormally folded proteins responsible for diseases like bovine spongiform encephalopathy (mad cow disease) and Creutzfeldt–Jacob disease. S5: Lichens are symbiotic associations where the fungal component (mycobiont) prepares food for the algal component (phycobiont). This statement is NOT correct. In lichens, the algal component (phycobiont) is autotrophic and prepares food for the fungal component, while the fungal component (mycobiont) provides shelter and absorbs mineral nutrients and water. Therefore, statements S2, S3, and S5 are NOT correct. The final answer is B. This question tests detailed knowledge about the structure, genetic material, and symbiotic relationships of these non-classified biological entities.