Question

Pheretima and its close relatives derive nourishment fron (a) sugarcane roots (b) decaying fallen leaves and soil organic matter (c) soil insects (d) small pieces of fresh fallen leaves of maize, etc.

Short answer

(b) is the correct answer as Pheretima and its relatives mainly feed on decaying fallen leaves and soil organic matter.

Step-by-step solution

Understanding the dietary habits of Pheretima

To solve this exercise, it's necessary to understand the feeding behaviour of Pheretima, also known as earthworms. Earthworms primarily consume dead and decaying matter along with soil, from which they extract nutrients.

Eliminating incorrect options

Based on their known feeding habits, we can eliminate the options that do not align with their diet. Pheretima does not feed on sugarcane roots specifically (a), and typically do not target living soil insects (c) as their primary food source. Though they may incidentally consume small pieces of fresh fallen leaves (d), it is not their primary source of nutrition.

Identifying the correct answer

Considering their feeding habits, the most appropriate answer to this exercise is (b) decaying fallen leaves and soil organic matter. This is what Pheretima and its close relatives primarily derive their nourishment from.

Key concepts

Earthworm Nutrition

Understanding the diet of earthworms, like Pheretima, is essential to comprehend their role in the ecosystem. These wriggly creatures have a specialized diet that consists mainly of dead and decaying plant materials such as leaves, twigs, and dead roots mixed with soil. The soil component of their diet is particularly important as it contains microorganisms that aid in digestion.

Earthworms consume this mixture through a process of ingestion, where the soil passes through their digestive tract. Along the way, the organic material is broken down by enzymes and the nutrients are absorbed, providing sustenance to the earthworm. An interesting fact about earthworms is that they don't have teeth. Instead, they use their muscular gizzard to grind down the soil and organic material they consume.

As they process large amounts of soil, earthworms significantly contribute to the cycle of nutrients in their environment, affecting both soil structure and fertility. Thus, they play a crucial role not just in their nutrition but also in maintaining healthy soil.

Decaying Organic Matter

Decaying organic matter includes a variety of materials such as fallen leaves, dead plants, and animal remains which undergo the process of decomposition. This process is essential to the nutrient cycle and aids in the production of rich, fertile soil called humus. Microorganisms like bacteria and fungi, along with detritivores such as earthworms, are responsible for breaking down these materials.

The decomposition process releases nutrients back into the soil, making them available for uptake by plants. Earthworms' eating habits, therefore, are a key component in this cycle. As they feed on the decaying matter and soil, they excrete what is known as worm castings, a type of natural fertilizer that enriches the soil. Earthworms are often referred to as 'nature’s tillers' because their burrowing behavior improves soil aeration and drainage, allowing for better root growth.

Soil Biodiversity

Soil biodiversity refers to the variety and variability of living organisms in the soil. These include an array of organisms from tiny bacteria and fungi to more complex nematodes and macro-organisms like earthworms. Biodiverse soils are capable of supporting a wide range of plant life and contribute to overall ecosystem health.

Earthworms are a keystone species in maintaining soil biodiversity. By burrowing and consuming soil and organic material, they create a hospitable environment for other soil organisms. Their actions lead to the mixing of soil layers, distribution of microorganisms, and the enhancement of nutrient availability.

The interaction between earthworms and soil microorganisms is particularly beneficial. For instance, as earthworms digest organic matter, they stimulate the activity of decomposer microbes, which in turn makes the soil more fertile. Soil biodiversity is integral to agriculture, water purification, and combating climate change as it influences the soil's ability to sequester carbon.