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

What is the correct sequence of nitrogen transformation for an ecosystem?

1. Bacteria → Animals → Plants → Soil

2. Plants → Animals → Bacteria → Soil

3. Bacteria → Plants → Animals → Soil

4. Animals → Bacteria → Soil → Plants

The correct answer is: Bacteria → Plants → Animals → Soil

The correct sequence of nitrogen transformation in an ecosystem begins with bacteria, which play a crucial role in the nitrogen cycle. Nitrogen-fixing bacteria convert atmospheric nitrogen into ammonia, a form that plants can uptake. This process takes place in the soil, where bacteria transform nitrogen into a usable form for plants. Next, plants absorb these nitrogen compounds and incorporate them into their tissues, making nitrogen available to herbivorous animals that consume the plants. When animals eat the plants, they obtain nitrogen, which is essential for their growth and development. Once animals excrete waste or die, decomposer bacteria break down these organic materials, returning nitrogen back into the soil in the form of ammonia or other nitrogenous compounds. This process enriches the soil, thus completing the nitrogen cycle and allowing plants to use this nitrogen once again. This cycle highlights the interdependent relationships between bacteria, plants, and animals within an ecosystem. It is important to note that the incorrect choices do not follow the natural order of nitrogen transformation, separating plants and animals from the essential role that bacteria play in the nitrogen cycle, or misrepresenting how these elements interact within the ecosystem.