Which of the following items is considered organic matter?

Organic matter refers to material that is derived from living organisms or contains carbon-based compounds. This includes a wide variety of substances, particularly those that were once part of plants or animals. Options such as wood, dogs, algae, and bacteria fall squarely within this definition, as they are all forms of life or biological products.

Wood comes from trees, which are living organisms, and contains organic compounds. Dogs are animals and comprise organic tissues. Algae, being simple photosynthetic organisms, are also biological in nature. Bacteria, though microscopic, are living organisms that play essential roles in nutrient cycling and decomposition.

In contrast, the other options include materials such as plastic bottles, sand and gravel, and glass and metal, none of which originate from or are derived from living organisms. These materials are inorganic; for example, plastic is a synthetic product made from petrochemicals, while sand and gravel are mineral-based, and glass and metal are entirely synthetic or naturally occurring minerals that have not come from biological sources. Thus, recognizing the various forms of organic matter helps in understanding ecological systems and their interactions.