Blood is a tissue because it is made up of different types of specialized cells.

Aside from red and white cells, what else does blood contain?

Plasma, water, salt, protein, platelets

Plasma is the liquid portion of the blood. Blood cells like red blood cells float in the plasma. Also dissolved in the plasma are electrolytes, nutrients and vitamins (absorbed from the intestines or produced by the body), hormones, clotting factors, and proteins such as albumin and immunoglobulins (antibodies that fight infection).