The color of the RBC\'s cytoplasm is (?) and it has a biconcave shape because of the lack of a (?). One of its functions, is to (?)(?). (?) = fill in the blank Solution The color of the RBC\'s cytoplasm is Red colour The cytoplasm of erythrocytes is rich in hemoglobin, an iron-containing biomolecule that can bind oxygen and is responsible for the red color of the cells t has a biconcave shape because of the lack of a nucleus. biconcave shape gives them a vastly greater surface area than a spherical cell of similar volume, which allows them to absorb oxygen more efficiently. Red blood cells achieve this shape by losing their nucleus and many other organelles during development. One of its functions, is to transport of O2.