Biology Regents Practice Exam

What does the process of nitrogen passing through food webs illustrate?

1. Nitrogen is removed and eliminated from ecosystems

2. Nitrogen is transferred directly from bacteria to humans

3. Chemical elements are combined and recombined in different ways

4. All elements remain in the ocean and are not transferred

The correct answer is: Chemical elements are combined and recombined in different ways

The process of nitrogen passing through food webs illustrates how chemical elements, including nitrogen, are continuously cycled and transformed in ecosystems. Nitrogen is an essential element for all living organisms as it is a key component of amino acids, proteins, and nucleic acids. In ecosystems, nitrogen undergoes various transformations: it can be fixed by certain bacteria from the atmosphere into forms that plants can absorb, such as nitrates. Herbivores obtain nitrogen by consuming plants, and then carnivores obtain nitrogen by consuming herbivores. This cycling involves different biochemical processes, such as nitrogen fixation, ammonification, nitrification, and denitrification. Through these processes, nitrogen is reconfigured and moves through different trophic levels, illustrating the dynamic interplay of chemical elements in biological systems. The other choices do not accurately capture the essence of the nitrogen cycle. Nitrogen is not eliminated from ecosystems but rather recycled, so the idea of it being removed contradicts its role in ecosystems. While there is some transfer of nitrogen between bacteria and humans, this is an oversimplification of the complex interactions in the food web. Finally, stating that all elements remain in the ocean ignores the broader ecological cycles that occur across land and sea.