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

What role do fungi play in the decomposition of Dissolved Organic Matter (DOM)?

1. They absorb DOM directly without any breakdown

2. They release digestive enzymes that break down DOM

3. They convert DOM into nitrogen gas

4. They accumulate DOM without affecting the ecosystem

The correct answer is: They release digestive enzymes that break down DOM

Fungi play a crucial role in the decomposition of Dissolved Organic Matter (DOM) by releasing digestive enzymes that break down complex organic compounds into simpler forms. This process is essential in nutrient cycling within ecosystems, as fungi effectively decompose materials such as dead plant and animal matter, thereby facilitating the release of nutrients like carbon, nitrogen, and phosphorus back into the environment. These enzymes work extracellularly, meaning they are released into the surrounding environment where they can break down large organic molecules into smaller units that can be absorbed by the fungi. By doing this, fungi not only partake in recycling nutrients but also help maintain the health of ecosystems by preventing the accumulation of organic debris. Other options suggest processes that do not accurately represent the role of fungi in decomposition. For example, absorbing DOM without breakdown implies that fungi would not contribute to nutrient recycling, while converting DOM into nitrogen gas would misrepresent the decomposition process, as fungi do not primarily convert organic matter into gaseous forms like nitrogen. Accumulating DOM without affecting the ecosystem does not align with the active role fungi play in nutrient cycling and ecosystem health.