For information about the IBâs achievements, initiatives and future strategy, read our annual review. 1  Read about the IB's leading professional development. 2  Read about the IB's support services for schools.
uk â /hem/ us â /hem/. âº the edge of a piece of cloth, such as the bottom edge of a skirt or dress, that is folded over and sewn so that it does not develop loose threads: I took the hem up/let the hem down. Thesaurus: synonyms and related words. Parts of clothes.
Hemoglobin is a protein that's made of four polypeptide chains. Each of these chains contains a heme group. Therefore, every hemoglobin molecule has the ability to bind four molecules of oxygen. Hemoglobin is the primary protein found in red blood cells, or erythrocytes.Each erythrocyte contains hundreds of thousands of hemoglobin molecules.ach of these chains contains a heme group. Therefore, every hemoglobin molecule has the ability to bind four molecules of oxygen. Hemoglobin is the primary protein found in red blood cells, or erythrocytes. Each erythrocyte contains hundreds of thousands of hemoglobin molecules.