Question

Open circulatory system is found in (a) Arthopods and molluscs (b) Annelids and Chordates (c) Annelids and arthopods (d) Fishes and molluses

Short answer

The correct answer is (a) Arthropods and molluscs.

Step-by-step solution

Understanding open circulatory system

An open circulatory system is a system in which the blood is not enclosed in blood vessels, instead, it fills cavities and spaces inside the body.

Identifying options

Looking at the options given, identify the organisms which have an open circulatory system. The options are arthropods, molluscs, annelids, chordates and fishes.

Selection of correct option

Study each option and make the choice based on the knowledge that arthropods and molluscs have an open circulatory system. Therefore, the correct answer is (a) Arthropods and molluscs.

Key concepts

Arthropods

Arthropods represent the largest phylum in the animal kingdom, encompassing familiar creatures such as insects, spiders, and crustaceans. One distinguishing feature of arthropods is their open circulatory system. Unlike closed systems that confine blood within vessels, the open circulatory system consists of a heart and an open hemocoel, where the fluid known as 'hemolymph' bathes the organs directly.

Arthropods' hemolymph is propelled by their heart into the hemocoel, and it flows freely around their body cavities, delivering nutrients and oxygen to their cells. This simplicity aligns with their generally small size and less active lifestyles, as the efficiency of direct diffusion is sufficient for their survival. Additionally, their exoskeleton provides an external structural support which compensates for the lack of extensive blood vessels.

Molluscs

Molluscs, a diverse group that includes snails, clams, and squids, also utilize an open circulatory system for the transportation of their bodily fluids. Their system consists of a heart, vessels, and an open hemocoel. The heart pumps hemolymph into the hemocoel, bathing the mollusc's internal organs.

Unlike more active animals with high metabolic rates that require efficient oxygen and nutrient distribution, many molluscs lead a slower paced lifestyle, making the less efficient open circulatory system adequate. Some molluscs like cephalopods (e.g., octopus and squid) are exceptions, as they have evolved more advanced closed circulatory systems to support their higher activity levels and larger body sizes.

Blood Circulation in Invertebrates

The concept of blood circulation in invertebrates varies greatly across different groups. While arthropods and molluscs employ open circulatory systems, other invertebrates like annelids (segmented worms) and most cephalopods (a subclass of molluscs) have closed circulatory systems.

In open circulatory systems, hemolymph directly bathes the cells and tissues, exchanging gases and nutrients without the distinction of separate blood and interstitial fluids. This contrasts with the closed system where blood is contained within vessels, allowing for faster and more controlled distribution of substances. Invertebrates have evolved diverse adaptations to their respective environments, leading to varied circulatory complexities that reflect their different ecological niches and lifestyles.

NEET Biology

NEET, the National Eligibility cum Entrance Test, is a preeminent exam in India for students aspiring to pursue undergraduate medical courses. Biology is a critical section in NEET, encompassing a wide array of topics including the circulatory systems of animals.

An understanding of the difference between open and closed circulatory systems is fundamental for NEET biology aspirants. The complexity of circulation in different animal groups is a topic that is often tested, highlighting the importance of mastering concepts like the open circulatory system present in arthropods and molluscs. With a strong grasp of such principles, students can excel in the zoology portion of the exam. Prospective medical students must comprehend these biological concepts not only to succeed in entrance exams but also to build foundational knowledge for future professional applications in the medical and biological sciences.