Blood is composed of the blood plasma and the blood cells and blood platelets.

The blood plasma gives the blood its liquid form and helps in the transportation of proteins, glucose, hormones and minerals required for the proper functioning of the body.

The blood cells are of two types: red blood cells and white blood cells. The red blood cells contain a protein called hemoglobin. Hemoglobin contains iron and helps in the absorption of oxygen from the lungs to distribute to each of the cells in the body. The people who have iron deficiency in their bodies feel tired because the blood is not able to supply oxygen to the cells without enough hemoglobin which is mainly composed of iron.

The white blood cells fight the disease causing pathogens that might enter the body. The people with less white blood cells are prone to frequent infections and diseases.

The blood platelets help in blood clotting after an injury. Platelets contain no DNA, but do contain clotting enzymes, and energy-producing mitochondria. The blood clotting is an important process to prevent excess loss of blood from the body. Once the blood flow is stopped by the clotting, the natural healing of an injury takes place.  If the blood does not stop its flow by blood clotting, the loss of blood can cause loss of hemoglobin also making it difficult to breathe and can even prove to be fatal in extreme cases.

You might ask if clotting of blood prevents the flow of blood why does it not clot when a mosquito or bed bug is sucking blood from a human? This is because these insects inject saliva into the blood stream of their host to thin the blood, and to prevent coagulation. It is this saliva that causes the intense itching and welts. The delay in the onset of itching gives the feeding bedbug time to escape into cracks and crevices.

If you are wondering what part of the blood helps transporting the carbon dioxide, it is the plasma that collects the carbon dioxide released by the cells and transports it to the lungs to be breathed out.