Circulatory System

Left ventricle, because it must pump oxygenated blood to the entire body with great force

Step 1: The heart has four chambers — two atria (upper) and two ventricles (lower). Step 2: Atria simply receive blood, so they do not need very thick walls. Step 3: Ventricles pump blood out of the heart, so they need thicker walls than atria. Step 4: The left ventricle specifically pumps oxygenated blood through the aorta to the ENTIRE body — a much longer and harder job than the right ventricle, which only pumps blood to the nearby lungs. Step 5: Because of this extra workload, the left ventricle has the thickest walls of all four chambers. Option A and B refer to atria which only receive b

They allow nutrients, oxygen, and waste materials to pass through their thin walls to and from body cells

Step 1: Capillaries are the smallest and thinnest blood vessels in the body. Step 2: Unlike arteries (which carry blood away from heart) and veins (which carry blood back to heart), capillaries have a different job. Step 3: Capillaries connect arteries to veins and are so thin that nutrients, oxygen, carbon dioxide, and waste products can pass through their walls. Step 4: This is how every individual cell in the body gets food and oxygen, and how waste is removed from each cell. Step 5: Option A describes the function of arteries, Option B describes veins, and Option D is completely incorrect

The heart is pumping blood 72 times per minute, causing arteries to stretch and relax 72 times per minute

Step 1: The pulse is the throbbing sensation felt in arteries near the skin surface. Step 2: Every time the heart pumps (beats), blood rushes into the arteries with force. Step 3: This force causes the elastic walls of arteries to stretch outward and then relax — this stretching and relaxing is what we feel as a pulse. Step 4: Since the heart pumps about 72 times per minute, the arteries stretch and relax 72 times per minute — so the pulse rate equals the heart rate. Step 5: Option B is wrong — veins do not contract to create pulse. Option C is wrong — capillaries are not involved in pulse. Op

Veins lie less deep under the skin and can be seen easily, while arteries lie deep under the skin and are not easily seen

Step 1: Arteries are located deep under the skin — this protects them because they carry blood under high pressure, and any injury to an artery would be very dangerous. Step 2: Veins, on the other hand, are located closer to the surface of the skin (less deep). Step 3: Because veins are near the skin surface, they can be seen through the skin as greenish-blue lines on the hands and legs. Step 4: Option A incorrectly states that oxygenated blood sinks deeper — the depth of blood vessels has nothing to do with the colour of blood. Step 5: Option C is wrong because arteries actually have THICKER