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

Which of the following statements about the phosphorus cycle is true?

1. Phosphorus exists only in the atmosphere

2. It is primarily found in gases

3. It returns to soil primarily through decaying matter

4. It does not involve plant uptake

The correct answer is: It returns to soil primarily through decaying matter

The statement regarding the phosphorus cycle being true is that it returns to soil primarily through decaying matter. In the phosphorus cycle, phosphorus is not present in the atmosphere as a gas, unlike carbon and nitrogen. Instead, phosphorus is primarily found in soil and water in forms such as phosphates. As plants and animals die, their organic matter decomposes, and phosphorus is released back into the soil, making it available for uptake by plants again. This process is crucial for maintaining the cycle of phosphorus in the ecosystem, as it allows the nutrient to be recycled within the soil and taken up by living organisms, supporting plant growth and, consequently, the entire food web. Understanding this cycle highlights the importance of decomposition and nutrient recycling in ecosystems, as phosphorus is vital for DNA, RNA, and ATP, which are essential for all living organisms.