Problem 88 - Objective Biology for NEET

Question

Closed circulatory system is present in (a) Nereis (b) Pheretima (c) Ascaris (d) Both (a) and (b)

Step-by-Step Solution

Answer

The correct answer is (d) Both (a) and (b).

Step 1: Understanding Closed Circulatory Systems

A closed circulatory system is one in which blood moves through the body in closed vessels. The blood does not directly communicate with tissues. It is typical of more complex organisms.

Step 2: Identifying the Organisms

In this step, classify the organisms mentioned in the exercise. Nereis is an annelid or segmented worm, often found in marine environments. Pheretima is a genus of earthworms. Ascaris is a genus of parasitic roundworms.

Step 3: Matching the Organisms to the Circulatory System

Nereis and Pheretima, both being annelids, possess a closed circulatory system. Ascaris, on the other hand, being a nematode, possesses a pseudocoelom and does not have a closed circulatory system.

Key Concepts

Annelid Circulatory System

The Annelid circulatory system represents a fascinating model of biological engineering. The closed circulatory system found in annelids, such as earthworms and polychaetes, includes blood vessels that maintain the blood separate from the body's interstitial fluid. This design allows for efficient transportation of nutrients, gases, and wastes.

• Blood is pumped by one or more hearts, promoting circulation throughout the organism.
• Unlike open circulatory systems, where blood bathes organs directly, annelids have a series of blood vessels that ensure blood travels to specific regions.
• Capillaries are the site of gas and nutrient exchange, and they connect the larger vessels.

The elegant efficiency of the annelid circulatory system underscores its evolutionary advantage, enabling these creatures to thrive in various environments.

Nereis

Nereis is a genus notably found in the polychaete class of the annelid phylum. These marine worms are distinguished by their segmented bodies and bristled appendages, which help them navigate their aquatic habitats.

Characteristics:

• Nereis species are known for their well-developed closed circulatory system, which is essential for their active lifestyle.
• They also have a complete digestive system and nervous system.
• One of the critical aspects of Nereis is their role in the marine ecosystem; they act as both predators and prey.
• Their closed circulatory system is instrumental in delivering oxygen and nutrients efficiently, enabling these worms to carry out complex movements.

The study of Nereis and its closed circulatory system provides insight into the evolutionary biology of annelids and their adaptation to marine life.

Pheretima

Pheretima is another genus within the Annelida phylum, specifically the oligochaete class, mainly comprising earthworms. This genus includes numerous species that contribute substantially to soil fertility and structure.

Adaptations:

• These terrestrial invertebrates have a closed circulatory system which is crucial for their burrowing lifestyle, enabling efficient gas exchange and nutrient distribution even in low-oxygen environments.
• Earthworms such as Pheretima are key bio-indicators and play a vital role in aerating the soil.
• They can regenerate lost segments, thanks to their segmented body structure and a significant number of stem cells.

Understanding the closed circulatory system of Pheretima enlightens the broader topic of physiological adaptation among diverse living organisms.