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

What service do decomposed organic materials in forests provide for cities?

1. They filter air pollutants

2. They release carbon dioxide for urban spaces

3. They retain water like a sponge and supply rivers

4. They produce oxygen for industrial use

The correct answer is: They retain water like a sponge and supply rivers

Decomposed organic materials in forests play a vital role in the ecosystem, particularly in relation to water management. When organic matter such as leaves, fallen trees, and other plant materials decompose, they improve soil structure and enhance its ability to retain water. This process leads to better water absorption and reduces surface runoff, which is crucial for maintaining healthy water supply levels in nearby rivers and streams. This water retention acts like a sponge, helping to regulate water flow and prevent flooding in urban areas during heavy rainfall. While air pollutants filtering or the production of carbon dioxide and oxygen are important ecological processes, they don’t directly link the role of decomposed materials in aiding water retention and supply to cities. Thus, the correct choice highlights how decomposed organic materials contribute to essential water management services that benefit urban environments.