OCR General Certificate of Secondary Education (GCSE) Biology Practice Exam

What happens to ammonia produced from decomposers in the nitrogen cycle?

1. It is released directly into the atmosphere

2. It is converted into nitrates by nitrifying bacteria

3. It is absorbed by plant leaves

4. It is stored in animal fat

The correct answer is: It is converted into nitrates by nitrifying bacteria

The process by which ammonia produced from decomposers is converted into nitrates by nitrifying bacteria is a critical step in the nitrogen cycle. When decomposers break down organic matter, they release ammonia as a byproduct. This ammonia then undergoes a transformation facilitated by nitrifying bacteria through a two-step process: first, ammonia is oxidized to nitrite, and then nitrite is further oxidized to nitrate. Nitrate is an essential nutrient that plants can readily absorb and use for growth. This conversion ensures that nitrogen, which is a vital component of amino acids and nucleic acids, becomes accessible to plants in a form they can utilize. This process plays a crucial role in maintaining the balance of nitrogen in the ecosystem and supporting plant life, which in turn sustains herbivores and higher trophic levels in food webs. The other choices do not accurately represent the fate of ammonia in the nitrogen cycle, as ammonia is not directly released into the atmosphere or absorbed by plant leaves in its ammonium form; instead, it must first be converted to nitrates. Additionally, ammonia is not stored in animal fat, as it needs to be processed into a stable form that can be utilized by living organisms.