Earthworms are known as ecosystem engineers as they play a significant role in the soil ecosystem. They help to break down dead plant material and animal waste into smaller particles which can be further decomposed by microorganisms. This process is called fragmentation.

Explanation:

Fragmentation is the process by which the larger particles of detritus are broken down into smaller ones by the action of earthworms. Earthworms ingest detritus along with soil particles and grind it in their muscular gizzard. The gizzard contains small rocks or gravel which helps in breaking down the detritus into smaller particles. The smaller particles of detritus are then excreted in the form of castings.

Significance of fragmentation:

1. Increase in surface area: The fragmentation process increases the surface area of the detritus, making it more accessible to microorganisms for further decomposition. This leads to the release of nutrients into the soil.

2. Soil structure: The excreta of earthworms, also known as castings, are rich in nutrients and are an important source of organic matter. The castings help to improve soil structure and increase soil fertility.

3. Aeration: The burrowing activity of earthworms helps to improve soil aeration by creating channels in the soil. This helps in the circulation of air and water in the soil.

4. Water retention: The channels created by earthworms also help in retaining water in the soil. This is because the channels act as reservoirs for water which can be used by plants during dry periods.

Conclusion:

Fragmentation is an important process in the soil ecosystem as it helps in the breakdown of detritus into smaller particles which are accessible to microorganisms. Earthworms play a significant role in this process as they help to increase soil fertility, improve soil structure, and enhance soil aeration and water retention.

Detritivores (e.g., earthworm) break down detritus into smaller particles. This process is called fragmentation. By the process of leaching, water- soluble inorganic nutrients go down into the soil horizon and get precipitated as unavailable salts.

• Bacterial and fungal enzymes degrade detritus into simpler inorganic substances. This process is called as catabolism. 

•Humification and mineralization occur during decomposition in the soil. Humification leads to accumulation of a dark coloured amorphous substance called humus that is highly resistant to microbial action and undergoes decomposition at an extremely slow rate. 

Hence the correct answer is option b