Blood is not a homogeneous mixture. It is a heterogeneous mixture that contains plasma, platelets, white blood cells, red blood cells and other types of cells.
A homogeneous mixture is a mixture made of components that are equally and uniformly distributed throughout the mixture. A heterogeneous mixture is a mixture in which components of the mixture are not uniformly distributed and are localized in different regions. Blood plasma, for example, is a homogeneous mixture. Blood itself, however, contains many different cells and particles that are not of equal concentration, and in some cases, these components can be localized and not equally distributed.