Biology · Body Fluids and Circulation · NEET
Open circulatory system: arthropods (like cockroach, prawn) and molluscs. Closed circulatory system: annelids (like earthworm, Nereis) and all chordates (fishes, frogs, humans). NCERT states this in exactly one line, so learn the four names in pairs: open = arthropods + molluscs; closed = annelids + chordates.
In closed circulation blood stays inside vessels, so the body can precisely regulate how much blood goes to each organ by narrowing or widening the vessels. In open circulation blood pours into open sinuses and the flow cannot be directed as accurately. NCERT says the closed pattern is 'more advantageous as the flow of fluid can be more precisely regulated.'
A sinus is a large open space or body cavity in the animal's body. In open circulation the heart pumps blood into these spaces, and the blood directly surrounds and bathes the tissues before returning to the heart. The blood-filled cavity is also called a haemocoel. There are no true capillaries here.
No. Both open and closed systems have a heart that pumps the blood. The difference is only in the path: in open circulation the heart pushes blood into open sinuses; in closed circulation the heart pushes blood into a sealed network of vessels. So 'open' refers to open spaces, not a missing heart.
Human circulation is a closed circulatory system. Blood always moves inside the heart and a closed branching network of arteries, capillaries and veins, and never spills freely into body cavities. This is true for all chordates.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
In open circulation blood leaves the vessels and fills open body spaces (sinuses); in closed circulation blood always stays inside a network of blood vessels.
Closed circulation is more efficient because blood flow to each organ can be precisely controlled by the vessels.
Open: cockroach (arthropod). Closed: earthworm (annelid) or human (chordate).
No, true capillaries are absent in open circulation. Blood flows through open sinuses instead of fine vessels.
It is a direct one-line NCERT fact that is often used in assertion-reason and match-the-column questions, and it links to the wider topic of circulatory patterns in animals.
