Why are red blood cells described as flexible?

Red blood cells are described as flexible primarily because their flexibility allows them to navigate through small blood vessels, such as capillaries. The structure of red blood cells makes them unique; they are shaped like biconcave discs, which increases their surface area for oxygen absorption and allows them to deform easily. This flexibility is crucial when red blood cells move through narrow spaces in the circulatory system, ensuring that they can deliver oxygen efficiently to various tissues and organs. By being able to change shape, red blood cells can pass through capillaries that are often smaller than their own diameter, facilitating effective circulation and oxygen transport throughout the body.