Michigan Test for Teacher Certification (MTTC) Secondary Integrated Science Practice test

Which cycle involves the fixation of carbon by plants into glucose?

1. Nitrogen Cycle

2. Water Cycle

3. Carbon Cycle

4. Phosphorus Cycle

The correct answer is: Carbon Cycle

The answer that identifies the carbon cycle as the correct choice highlights the essential role plants play in this process through photosynthesis. During photosynthesis, plants convert carbon dioxide from the atmosphere into glucose, a type of sugar that serves as an energy source for the plant and forms the basis of the food chain. The carbon cycle encompasses various processes, including carbon fixation, where atmospheric carbon is transformed into organic compounds, and respiration, where animals and plants release carbon back into the atmosphere. This cycle is fundamental for regulating Earth's climate and supporting life by facilitating the transfer of carbon between the atmosphere, biosphere, oceans, and geosphere. In contrast, the nitrogen cycle deals with the transformation of nitrogen and its compounds in the environment, while the water cycle describes the continuous movement of water through evaporation, condensation, and precipitation. The phosphorus cycle focuses on the movement of phosphorus through geological and biological systems but does not involve carbon fixation. Hence, the carbon cycle is the only cycle that specifically addresses the conversion of carbon into glucose by plants.