Problem 42 - Objective Biology for NEET

Question

Which of the following has a closed type of circulatory system? (a) Cockroach (b) Fish (c) Scorpion (d) Mollusc

Step-by-Step Solution

Answer

Out of the provided options, fish (option b) possess a closed circulatory system.

Step 1: Identifying the Type of Circulatory System in a Cockroach

Cockroaches have an open circulatory system, in which the blood (hemolymph) isn't enclosed in blood vessels but is free in cavities (hemocoel) within their bodies and in direct contact with their body cells.

Step 2: Identifying the Type of Circulatory System in a Fish

Fish have a closed circulatory system. They have a heart and blood vessels, which carry the blood through the entire body without it being in direct contact with body cells.

Step 3: Identifying the Type of Circulatory System in a Scorpion

Scorpions, like other arthropods, exhibit an open circulatory system. The hemolymph is not enclosed in blood vessels but sloshes around in an open cavity (hemocoel).

Step 4: Identifying the Type of Circulatory System in a Mollusc

Molluscs like snails possess an open circulatory system where the hemolymph circulates freely within hemocoel.

Key Concepts

Circulatory System

The circulatory system is a network that allows blood to travel throughout the body, delivering nutrients and oxygen to cells and removing waste products.

There are two main varieties of circulatory systems found in the animal kingdom: closed and open. A closed circulatory system, found in vertebrates such as fish, mammals, birds, and reptiles, involves blood circulating through a continuous series of vessels. This system is efficient at transporting blood quickly and allows for higher metabolic rates.

The closed system includes arteries, veins, and capillaries. Arteries carry oxygen-rich blood away from the heart to the body's tissues, while veins carry oxygen-depleted blood back to the heart. Capillaries, the smallest blood vessels, facilitate the exchange of nutrients, gases, and waste between the blood and cells.

Open Circulatory System

An open circulatory system is characterized by the absence of a continuous system of blood vessels. Instead, the fluid known as hemolymph is pumped by the heart into the body cavity or hemocoel, where it directly bathes the organs and tissues.

This system, typical for invertebrates such as arthropods and some molluscs, is less efficient in transporting fluids compared to the closed system. However, it requires less energy and is considered to be sufficient for organisms with slower metabolic rates. Invertebrates with an open circulatory system rely on body movements to facilitate effective circulation of hemolymph.

Hemolymph

Hemolymph is the fluid equivalent to blood in animals with an open circulatory system. This fluid has multiple roles—it transports nutrients to cells, removes waste products, and sometimes even acts as a hydrostatic skeleton to support the body.

Unlike blood, hemolymph does not contain red blood cells but may contain hemocyanin or other pigments to transport oxygen. It also contains hemocytes, which play a role in immune defense. Hemolymph is often a mix of blood and interstitial fluid, the fluid that bathes cells in a multicellular organism.

Hemocoel

The term 'hemocoel' refers to the primary body cavity found in invertebrates with an open circulatory system. It acts as a reservoir for hemolymph and is typically divided by a series of membranes or septa.

The hemocoel is not a blood vessel system, but rather an interconnected series of sinuses or spaces among the organs. The hemolymph flows through the hemocoel and is pushed and directed by the movement of the animal's body and its breathing patterns. When the heart relaxes, hemolymph is drawn back toward the heart, which facilitates the circulation process.