Human Blood (image) Friedrich-Schiller-Universitaet Jena Caption Around 40 percent of the blood consists of red blood cells. They contain the red pigment hemoglobin and are responsible for the transport of oxygen. Credit Jan-Peter Kasper/FSU Usage Restrictions None Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.