Ontario Grade 9 Science Class Practice Exam 2025 - Free Grade 9 Science Practice Questions and Study Guide

Bacteria and fungi are the primary organisms responsible for decomposing matter into nutrients. These microorganisms play a crucial role in the ecosystem by breaking down dead organic material, such as plant and animal remains. As they decompose this matter, bacteria and fungi convert complex organic substances into simpler compounds, which are then returned to the soil. This process enriches the soil with nutrients, making them available for plants to absorb, thereby facilitating the growth of new plant life.

In contrast, while insects can assist in decomposition by breaking down larger organic matter into smaller pieces, their role is more about physical breakdown rather than chemical decomposition. Similarly, mammals and larger animals do not primarily engage in the decomposition process; they may contribute to the cycle by consuming organic matter or providing waste, but they do not carry out the same essential nutrient-recycling functions as bacteria and fungi do. Plants are integral to the ecosystem as primary producers, but they do not decompose organic matter themselves; they utilize the nutrients released by decomposers. Thus, the specialized roles of bacteria and fungi in nutrient recycling make them the correct answer to the question.