All humans have blood, but what is blood? What is the composition of blood? What is the purpose of blood? How is blood produced? How does the blood circulatory system work? What are the blood types? Do all animals have blood? Is blood always red? This report will address these questions and provide a scientific answer to each. Say no to plagiarism. Get a tailor-made essay on "Why Violent Video Games Shouldn't Be Banned"? Get an original essay Blood is composed of two components: plasma and formed elements. Plasma, a transparent extracellular fluid, is made up of a mixture of proteins, enzymes, nutrients, waste, hormones and gases. Since plasma is composed mainly of water, it is created by the absorption of drinks by the intestine. These plasma proteins transport hormones throughout the body. The elements formed are enclosed within a plasma membrane and can be further divided into three categories: erythrocytes (red blood cells), leukocytes (white blood cells) and platelets. They are all produced in the medulla of the arch. The main purpose of erythrocytes is to supply oxygen to the body's tissues. These red blood cells are rich in hemoglobin; Hemoglobin is the cause of the red color in our blood. Leukocytes are the cells that protect the body from infectious diseases. Finally, platelets play the role of stopping bleeding by interacting with clotting proteins. Together they also play additional roles essential to our survival, such as transporting essential nutrients to cells, transporting carbon dioxide to the lungs to be exhaled, and regulating body temperature and acidity levels. The heart and blood vessels play a vital role in the blood circulatory system. Blood is taken away from the heart through the arteries and returned to the heart through the veins. Blood groups are classified based on the presence and absence of antibodies. Antibodies are a type of protein produced by the immune system to help fight antigens. Blood type plays a crucial role during blood donations and transfusions as antibodies will attack other blood cells with an unrecognizable antigen. There are four main blood groups, A, B, AB and O, and each group can be RhD positive or negative. RhD refers to a form of antigen found in red blood cells. Please note: this is just a sample. Get a custom paper from our expert writers now. Get a Custom Essay An interesting fact is that not all animals have blood. Many invertebrate animals such as jellyfish do not have blood as they are able to absorb nutrients and excrete waste directly. As mentioned above, hemoglobin causes our blood to be red. In other animals, blood can come in a variety of colors. Earthworms and inspectors have green blood, starfish have yellowish blood, and lobster have blue blood.