For most animals, blood provides essential nutrients to organs, circulates oxygen throughout the body, and forms clots to close up wounds. But not all blood is the same. If you’ve ever gotten a cut, you know that humans have dark-red blood, like most mammals. But if a crustacean, insect, or worm gets a cut, you might be surprised at the color it bleeds!
Blood is made up of many different elements—it isn’t one homogenous, or uniform, fluid. Blood has four main components. There are cells that carry oxygen (called red blood cells in humans) and cells that fight infection (called white blood cells in humans). The smallest type of cell in blood, platelets, slow or stop bleeding. All these cells are carried in a fluid called plasma, which contains proteins, electrolytes, and more.