Question

An open circulatory system occurs in the
A. Reptiles
B. Birds
C. Insects
D. Annelids

Answer 1

Hint: An open circulatory system is seen in insects, molluscs, and invertebrates. They pump blood into haemocoel which diffuses blood back to the circulatory systems between cells. The blood is pumped by the heart and then into body cavities where the tissues are surrounded by blood.

Complete answer: Majority of the reptiles have a three-chambered heart which is similar to an amphibian's heart which directs blood to systemic circuits and the pulmonary system. The septum divides the ventricle effectively, which results in less mixing of deoxygenated blood and oxygenated blood.
-Birds have a very efficient cardiovascular system that permits them to meet all the metabolic demands of flight. This system does not only deliver oxygen to the blood cells but also has an important role in maintaining a bird’s body temperature. Bird’s circulatory system is generally called an avian circulatory system and it consists of a heart and blood vessels to transport the blood.
-Even insects have an open circulatory system like arthropods as opposed to our close circulatory system. In human beings, our blood travels only through blood vessels but in an insect’s blood called hemolymph flows freely throughout the body.
-Annelids have a closed circulatory system which means that the blood is contained within blood vessels and heart and does not drain into the body cavities.
Hence, the correct answer is option C, i.e., Insects.

Note: An open circulatory system is a system in which the blood and the interstitial fluid are allowed to mix in an organism. Animals with an open circulatory system do not have true blood as they are mixed with other body fluids.