Final answer:
The CO₂ and O₂ cycle in a terrarium with only plants is driven by photosynthesis, which absorbs CO₂ and releases O₂, and respiration, which consumes O₂ and releases CO₂. The correct answer to the student's question is that CO₂ is absorbed by plants during photosynthesis and O₂ is released as a byproduct.
Step-by-step explanation:
Within a terrarium containing only plants, the carbon dioxide (CO₂) and oxygen (O₂) cycle operates through the processes of photosynthesis and respiration. During photosynthesis, plants absorb CO₂ from the air to produce organic compounds, and as a byproduct, they release O₂. Conversely, when plants undergo respiration, they consume O₂ to break down these organic compounds, releasing CO₂ back into the terrarium environment.
In the context of the question provided, the correct statement is: 2) CO₂ is absorbed by plants during photosynthesis and O₂ is released as a byproduct. This is because photosynthesis is the process in which plants use sunlight to convert carbon dioxide and water into glucose and oxygen. Even though plants also respire, during the daytime, the rate of photosynthesis is typically higher than the rate of respiration, resulting in a net output of oxygen.