Certified Professional Horticulturist (CPH) Practice Exam

Organic matter comes from decaying plants and animals as well as animal excretions, but also includes:

1. Living organisms

2. Essential nutrients

3. Some carbon-based materials

4. Soluble salts

The correct answer is: Living organisms

Organic matter is composed primarily of decomposed materials from plants and animals, including their excretions. Additionally, it encompasses living organisms such as microbes, fungi, and other small creatures that are a part of the ecosystem. These living organisms contribute to the dynamic nature of organic matter through processes like decomposition and nutrient cycling. They play a vital role in breaking down complex organic materials into simpler forms that can be utilized by plants and other organisms. While essential nutrients are necessary for plant growth, they don't constitute organic matter itself; instead, they are often found within it. Similarly, carbon-based materials may include various substances, but not all carbon-based materials are classified as organic matter, especially synthetic or non-decomposable materials. Soluble salts are inorganic compounds and do not contribute to the definition of organic matter. Therefore, the inclusion of living organisms as a component of organic matter emphasizes the ecosystem's interconnectedness and the importance of biological activity in maintaining soil health and fertility.