Assertion (A): Viruses are considered obligate parasites. Reason (R): Viruses lack their own metabolic machinery and require a host cell to replicate. MCQ with Answer and Explanation

Explanation:
The tundra biome, found in Arctic and Antarctic regions, has permanently frozen subsoil (permafrost), extremely low temperatures, short growing seasons, and vegetation limited to mosses, lichens, grasses, and dwarf shrubs. Taiga is the boreal coniferous forest, savanna is tropical grassland, temperate deciduous forest has distinct seasons. Tundra is the coldest biome.

Explanation:
The pleural cavity between the visceral and parietal pleura contains a thin layer of pleural fluid, lubricating the surfaces to reduce friction during lung expansion and contraction. Synovial fluid is in joints, cerebrospinal fluid surrounds the CNS, lymph is in the lymphatic system. Pleural effusion is excess accumulation.

Explanation:
The domesticated silkworm, Bombyx mori, is a monophagous insect, meaning it feeds almost exclusively on the fresh leaves of the mulberry plant (primarily Morus alba). The quality and quantity of silk produced are directly dependent on the quality of the mulberry leaves consumed by the larvae. While tasar silkworms feed on oak and castor, the common mulberry silkworm requires Morus alba.