Blood is composed of cells and cell fragments in an aqueous solution (plasma). Blood makes up about 7-8% body weight for an adult human being. Plasma constitutes almost 55% of the blood volume and contains almost 90% water. Red blood cells (or erythrocytes or RBC) make up for (pretty much) the rest of the blood volume and constitute about 45% of our blood. White blood cells (or WBC or leukkocytes) constitute only 0.7% of our blood. The RBCs transport oxygen (due to presence of hemoglobin) and carbon dioxide (to a lesser extent as compared to oxygen transport). WBC are part of our immune system and help us fight infections.
An interesting fact about blood: our blood is red in color, while that of some other species may have some other color. For example, insects have yellow or green blood.
the red liquid that circulates in the arteries and veins of humans and other vertebrate animals, carrying oxygen to and carbon dioxide from the tissues of the body.