Which organisms are commonly found in soil?

The organisms that are commonly found in soil include worms, insects, fungi, and bacteria. These organisms play critical roles in soil health and ecology. For example, earthworms help aerate the soil and improve its structure by decomposing organic matter. Insects contribute to the breakdown of organic materials and also serve as prey for other soil-dwelling creatures. Fungi are essential for nutrient cycling; they decompose complex organic materials and form symbiotic relationships with plant roots, aiding in nutrient absorption. Bacteria facilitate nutrient cycling as well, breaking down dead organic matter and contributing to the formation of humus.

In contrast, trees, shrubs, and grasses are primarily above-ground plants that may depend on the soil for nutrients and anchorage but do not primarily inhabit the soil itself in the same way as the organisms listed in the correct answer. Birds, mammals, and reptiles are larger organisms that may interact with the soil environment but are not considered soil-dwelling organisms. Thus, the presence of worms, insects, fungi, and bacteria in the soil illustrates a diverse and critical community essential for maintaining soil fertility, structure, and overall health.