Biology Regents Practice Exam

What happens to chemical elements in ecosystems, such as nitrogen?

1. They are eliminated after use

2. They are damaged and lost over time

3. They are reused and cycled through food webs

4. They remain static and unchanged

The correct answer is: They are reused and cycled through food webs

In ecosystems, chemical elements like nitrogen are essential for the growth and survival of organisms. Instead of being eliminated or lost permanently, these elements undergo a continuous cycle— often referred to as biogeochemical cycles. For instance, nitrogen is introduced into the ecosystem through processes like nitrogen fixation, where atmospheric nitrogen is converted into forms usable by plants. After plants take up nitrogen, it's incorporated into proteins and other essential compounds. When animals consume these plants, the nitrogen is transferred through the food web. When organisms excrete waste or die, decomposers break down their bodies, returning nitrogen to the soil in forms that can again be used by plants. This cycling of nitrogen is crucial for maintaining ecosystems, as it allows for ongoing productivity and sustains life. Therefore, the correct answer reflects the dynamic nature of chemical elements in ecosystems, highlighting their role in maintaining ecological balance through constant reuse and cycling.