Question

Nephridia helps in the excretion and osmoregulation in (a) Nereis (b) Pheretima (c) Hirudinaria (d) All of these

Short answer

The answer is (d) All of these.

Step-by-step solution

Understand Nephridia

Nephridia are tubular excretory structures of an annelid's excretory system. They filter out fluid from the blood and coelomic fluid and release the waste from the body. This helps in both excretion and osmoregulation, maintaining a balance of water and salts in the animal's body.

Evaluate the Choices

Nereis is a genus of polychaete worms, Pheretima is a genus of earthworms, and Hirudinaria is a type of medicinal leech. All three belong to the Annelida phylum of segmented worms, which characteristically have a system of tubular nephridia for their excremental functions. Therefore, nephridia helps in the excretion and osmoregulation in all of these organisms.

Key concepts

Excretion and Osmoregulation

Excretion and osmoregulation are vital life processes that all living organisms perform to maintain homeostasis. Excretion involves the removal of metabolic waste products from an organism. This process prevents waste accumulation, which could lead to toxic conditions in the body. On the other hand, osmoregulation is the regulation of water and ion concentration within an organism's body. This ensures cells function effectively, as it balances salt and water levels.

In the case of annelids, like earthworms, these processes are closely linked. Nephridia are the primary structures facilitating both excretion and osmoregulation. They effectively manage the balance between excreting waste and retaining necessary substances, like salts and water, contributing to the organism's overall health and equilibrium. Efficient function of nephridia ensures these worms can thrive in various environments by managing their internal conditions precisely.

Annelida

Annelida is a phylum of segmented worms, known for their distinctive body segmentation. The name "Annelida" itself originates from the Latin word "anellus," meaning "little ring," highlighting this segmented nature. This group includes a diverse range of organisms such as earthworms, leeches, and polychaetes.

One of the key features of annelids is their hydrostatic skeleton, which is supported by fluid-filled segments called coeloms. This structure provides them with flexibility and strength. Annelids also display a well-developed internal structure, including a complete digestive system, closed circulatory system, and specialized excretory organs known as nephridia.

• Earthworms, belonging to the genus Pheretima, play vital roles in soil aeration and organic matter decomposition.
• Nereis are marine polychaetes known for their bristled bodies and vibrant colors.
• Hirudinaria includes medicinal leeches, often used in medical treatments.

Each of these organisms uses nephridia to manage their waste and water balance, showing the diverse adaptation of this excretory system among the annelids.

Earthworm Physiology

Earthworms, particularly of the genus Pheretima, exhibit fascinating physiological traits adapting them to life underground. Their bodies are segmented, which aids in movement through soil by contracting and relaxing muscles in succession.

Earthworms possess a simple yet effective circulatory system categorized as "closed." This means that the blood flowing internally is enclosed within vessels, circulating nutrients, gases, and waste products efficiently. Oxygen is absorbed directly through their moist skin, requiring them to inhabit environments that support this respiratory method.

• The digestive system begins with the mouth, leading to a muscular pharynx and a long intestine, aiding in the decomposition of organic material.
• Through their skin, earthworms exchange gases, which is crucial for their survival in moist environments.
• Their nervous system consists of a ventral nerve cord with segmental ganglia providing local control over movements.

The most remarkable aspect of earthworm physiology is perhaps their excretory system, which includes several types of nephridia, intricately involved in expelling waste and managing body fluid balance.

Excretory System in Worms

The excretory system in annelids, such as earthworms, is quite sophisticated despite their simple overall structure. Nephridia, the core components of this system, are scattered across each segment of the worm's body, allowing precise management of fluids and waste.

Each nephridium is a tubular structure functioning similarly to kidneys in higher organisms. The process begins with filtering body fluids in the coelomic cavity. The nephridia then selectively reabsorb necessary components like salts and water while expelling the rest as waste.

• Nephridia vary slightly between species but generally include protonephridia and metanephridia forms.
• Protonephridia are simpler, and metanephridia provide more complex and efficient waste processing.
• They interface directly with the organism's circulatory system to maintain balance.

This excretory mechanism allows earthworms and other annelids to adapt to different environmental conditions by efficiently handling their waste and osmoregulatory needs.