TeXes Science Practice Test

Which natural process primarily absorbs carbon dioxide from the atmosphere?

1. Respiration

2. Photosynthesis

3. Combustion

4. Decomposition

The correct answer is: Photosynthesis

Photosynthesis is the natural process through which plants, algae, and some bacteria convert carbon dioxide and sunlight into glucose and oxygen. During this process, chlorophyll in plant cells captures sunlight, which provides the energy needed to transform carbon dioxide — absorbed from the atmosphere through small openings in leaves known as stomata — and water into sugar. This is vital not only for plant growth but also for reducing atmospheric carbon dioxide levels, thus playing a crucial role in regulating the Earth's climate. While respiration does release carbon dioxide, combustion produces CO2 as a byproduct of burning, and decomposition involves the breakdown of organic matter, releasing carbon back into the atmosphere. None of these processes contribute to the absorption of atmospheric carbon dioxide in the way that photosynthesis does. Therefore, photosynthesis stands out as the primary natural mechanism for absorbing carbon dioxide from the atmosphere.