PYQ Bank — UPSC Civil Services

Statement 1 is correct: guide RNA directs Cas9 to specific DNA sequences for precise editing.

Statement 2 is incorrect: CRISPR-Cas9 can be used in both somatic and germline cells, though germline editing raises ethical concerns.

Statement 3 is correct: CRISPR-Cas9 is derived from bacterial immune mechanisms that bacteria use against viruses.

Therefore, only statements 1 and 3 are correct.

This demonstrates Rayleigh scattering, where shorter wavelengths (blue light) scatter more readily than longer wavelengths.

During the day, blue light is scattered throughout the sky, making it appear blue.

At sunset, light travels through a greater thickness of atmosphere to reach our eyes, causing blue light to scatter away, leaving only the longer wavelengths (red and orange) visible.

Options A, C, and D misunderstand the physical mechanisms involved in light scattering and atmospheric optics.

Option C is incorrect because dark matter has NOT been directly observed or photographed, despite decades of research.

Its existence is inferred through indirect gravitational effects on visible matter and radiation.

Options A, B, and D are all correct: dark matter comprises ~85% of matter in the universe, its existence was inferred from galaxy rotation curves, and it forms halos around galaxies affecting their dynamics.

Dark matter remains one of the greatest unsolved mysteries in physics.

Statements 1, 2, and 3 correctly describe mechanisms of antibiotic resistance: bacteria can enzymatically inactivate antibiotics, acquire resistance genes through horizontal gene transfer from other bacteria, and mutations conferring resistance are selected for under antibiotic pressure.

Statement 4 is incorrect because antibiotic exposure does not directly cause permanent genetic changes; rather, it selects for pre-existing or newly mutated resistant variants.

Understanding these mechanisms is crucial for developing strategies to combat antibiotic resistance, a major global health threat.

Statements 1 and 2 are correct: Aurora Borealis results from solar wind particles channeled by Earth's magnetic field colliding with atmospheric gases, and magnetospheric substorms occur from magnetic reconnection releasing stored energy in the magnetotail.

Statement 3 is incorrect: Van Allen Belts are regions of trapped charged particles (mainly from solar wind and cosmic rays) held by Earth's magnetic field, not formed by cosmic ray concentration due to atmospheric pressure.

The Van Allen Belts are stable radiation zones, not dynamic phenomena caused by atmospheric pressure variations.