Orange Standards of Learning (SOL) Practice Exam

In a closed system, producers like a fern can generate oxygen through photosynthesis when light is available, using carbon dioxide and water. The fern acts as a source of oxygen for the salamander, so the salamander that has the fern benefits from higher oxygen levels and can breathe more easily. The other salamander, without the plant, relies on the limited oxygen already in the box and would experience decreasing oxygen as respiration continues, making survival harder. The described reasoning highlights how the fern helps maintain air quality in the sealed environment, giving the salamander with the fern the better odds of surviving.