Biology STAAR (State of Texas Assessments of Academic Readiness) Practice Test

In the carbon-oxygen cycle, what process do plants primarily utilize to incorporate carbon?

1. Cellular respiration

2. Photosynthesis

3. Decomposition

4. Evaporation

The correct answer is: Photosynthesis

Plants primarily utilize photosynthesis to incorporate carbon into their structures. During this process, plants take in carbon dioxide from the atmosphere through small openings on their leaves called stomata. Using the energy from sunlight, they convert carbon dioxide and water into glucose (a form of sugar) and oxygen. The chemical equation for photosynthesis can be summarized as: 6CO₂ + 6H₂O + light energy → C₆H₁₂O₆ + 6O₂ Here, carbon dioxide (CO₂) is the source of carbon that is transformed into organic matter, primarily glucose, which plants use for energy and growth. This essential process not only contributes to plant development but also plays a vital role in removing carbon dioxide from the atmosphere, thereby contributing to the balance of the carbon cycle. Other processes listed, such as cellular respiration and decomposition, are important in the larger context of carbon cycling but do not primarily involve the incorporation of carbon by plants. Evaporation relates to the water cycle and does not play a direct role in how plants obtain or incorporate carbon.