Final Answer:
Bacteria in soil feed on organic matter.
Step-by-step explanation:
Bacteria in soil play a crucial role in nutrient cycling and decomposition processes. Their primary source of nutrition is organic matter, making option A the correct answer. Organic matter includes plant and animal residues, such as dead leaves, roots, and other decaying materials. As these organic substances break down, they release nutrients that bacteria use for their growth and metabolism.
The decomposition process initiated by bacteria is essential for maintaining soil fertility. When organic matter is decomposed, it transforms into humus—a dark, nutrient-rich material that enhances soil structure and water retention. Bacteria break down complex organic compounds into simpler forms, releasing carbon, nitrogen, phosphorus, and other essential elements. This not only benefits the bacteria themselves but also contributes to the overall health of the soil, supporting plant growth.
In contrast, options B, C, and D represent other components of the soil food web. Nematodes, protozoa, and fungi are indeed present in soil ecosystems, but they serve as part of the intricate interactions within the microbial community. Nematodes, for instance, may be predators of bacteria, while fungi participate in the decomposition of organic matter alongside bacteria. However, when it comes to the direct source of nutrition for bacteria, organic matter stands out as the primary substrate.