Meaning & Definition

Correct answer: B. Oxbow lake

Direct answer: B, an oxbow lake. A meander is a bend in a river. Erosion works on the outside bank, while deposition builds the inside bank, so the bend becomes more curved and its neck becomes narrow. During a flood or strong flow, the river may cut through this narrow neck and take a shorter, straighter course. The abandoned loop remains separated from the main channel and often has a horseshoe shape; it is called an oxbow lake. A lagoon is a coastal water body, C is a glacial lake formed in a hollow left by melting ice, and D is an underground cavity in rock. Memory cue: a cut-off river bend looks like an oxbow, so it becomes an oxbow lake.

Correct answer: A. Aerobic respiration

Direct answer: A, aerobic respiration. In aerobic respiration, cells use oxygen to help release usable energy from food. Oxygen acts as the final acceptor in the energy-releasing chain inside many cells, allowing efficient production of energy for movement, growth, repair, and other life functions. If atmospheric oxygen were absent, organisms that depend on aerobic respiration would be seriously affected, although some organisms can use anaerobic pathways. Option B is wrong because light scattering mainly depends on interactions with molecules and particles and does not require oxygen specifically. Option C is wrong because argon’s chemical inertness is a property of argon, not a process that requires atmospheric oxygen. Option D is wrong because neon’s rarity is related to its abundance and distribution, not to oxygen availability. Memory cue: aerobic means “with oxygen,” so oxygen loss directly threatens aerobic respiration.

Correct answer: A. Ultraviolet radiation

Direct answer: A, ultraviolet radiation. Ozone in the stratosphere absorbs a substantial part of incoming ultraviolet radiation, especially wavelengths that can damage living tissues. This absorption acts like a protective filter. When the ozone layer becomes thinner, its filtering capacity is reduced, so a greater amount of ultraviolet radiation can reach Earth’s surface. Excess ultraviolet exposure can harm skin and eyes and can damage plants and other organisms. Option B is wrong because ozone depletion is not described as an increase in infrared radiation only; infrared energy has different sources and atmospheric interactions. Option C is wrong because radio waves are not the radiation specifically screened by stratospheric ozone in this context. Option D is wrong because sound is a mechanical wave that needs a medium and is not solar radiation filtered by ozone. Memory cue: ozone is a UV shield—less ozone means more UV can pass through.