Zoology MCQs for NEET — Practice Questions with Answers

An open circulatory system is present in arthropods and most molluscs (except cephalopods). In an open circulatory system, the blood is not always confined within blood vessels and instead flows freely through cavities in the body, coming into direct contact with tissues.

An artificial pacemaker is a device that is implanted in patients to help control abnormal heart rhythms. This is particularly necessary for those suffering from arrhythmias, where the heart beats irregularly - either too fast, too slow, or with an irregular rhythm. The pacemaker sends electrical pulses to prompt the heart to beat at a normal rate.

The postcaval vein, also known as the inferior vena cava, has a wide lumen to accommodate the large volume of blood returning to the heart from the lower parts of the body. It is one of the largest veins in the body and has a wider lumen compared to arteries and other veins.

In haemodialysis, heparin is added to the blood to prevent clotting as it passes through the dialysis machine. After the blood is purified, antiheparin is added to neutralize the effect of heparin before the blood is returned to the patient's body. This ensures that the patient's blood can clot normally once back in their circulation.

Serotonin is known to cause the constriction of blood vessels. This is an important function because it helps regulate blood flow and blood pressure. In conditions like a bleeding injury, serotonin is released to help minimize blood loss by narrowing the blood vessels.

Arteries have thicker walls compared to veins. This is because arteries need to withstand higher pressure as they carry blood away from the heart. The thick muscular and elastic walls help maintain the pressure and ensure efficient blood flow.

The pulmonary vein is responsible for carrying oxygenated blood from the lungs to the heart. This is a unique characteristic as most veins carry deoxygenated blood, but the pulmonary vein is an exception, carrying oxygen-rich blood to the heart to be pumped into the systemic circulation.

The diaphragm is a major muscle involved in respiration, and it receives its blood supply from the phrenic arteries. The phrenic arteries, which branch off from the thoracic aorta, specifically supply the diaphragm. Hence, option o2: Phrenic artery is correct.

The iliac artery is a major artery that supplies blood to the lower regions of the body. It specifically carries blood to the hind limb, among other areas. Therefore, option o3: Hind limb is correct.

Blood capillaries are the smallest blood vessels in the body and are composed of a single layer of endothelial cells. This single-cell thickness allows for efficient exchange of gases, nutrients, and waste products between blood and surrounding tissues. Thus, option o1: Blood capillary is correct.