Which of the following best describes a role of atmospheric gases?

• A. They absorb all solar radiation
• B. They provide oxygen for respiration and carbon dioxide for photosynthesis
• C. They form permanent solid layers
• D. They block all sunlight

Answer: (B)

Atmospheric gases enable life by providing oxygen for respiration and carbon dioxide for photosynthesis. Animals and many microbes use O2 to release energy from food, while plants, algae, and some bacteria use CO2 to make sugars through photosynthesis, releasing O2 in the process. This gas exchange sustains ecosystems and links respiration and photosynthesis in a global cycle. The other statements aren’t fitting because the atmosphere isn’t a solid layer and it doesn’t block all sunlight; it’s mostly transparent to visible light, with only certain wavelengths absorbed by specific gases, so life still receives sunlight to drive these processes.