Blood is composed of cells and fluid, contain many inorganic and organic
             molecules. Functions of blood could be falls into three categories:
             transport, defense and regulation, they all have different function. Blood
             transport oxygen and nutrients and removes waste from the body. It also
             transports hormones, which control the body's organ. Blood defense
             pathogens such as bacteria and viruses and it clots, which prevents the loss
             of blood. In regulatory functions, blood helps maintain body temperature
             A molecule cells use in cellular respiration, transport oxygen, is called
             red blood cells. Red blood cells also known as erythrocytes, they are very
             small. There are about 4 to 6 millions of red blood cells in our whole
             blood. It's containing a respiratory pigment called hemoglobin. It's
             carries oxygen and it is red in color. In red blood cell, it's contains
             about 200 million hemoglobin molecules. If we losing a big amount of
             hemoglobin in our blood, our blood will become thicker, so then is hard to
             All blood cells are produced from stem cells with in the red bone marrow.
             Stem cell, which can divide, and producing new cells into specific type of
             cells. Red blood cells can only live for 120 days, after that, they will
             destroyed in the liver and spleen and there are about 2 million cells are
             destroyed per second. Therefore, an equal number much be produced to keep
             the cell count in balance. People who are lack of hemoglobin will suffer
             Blood that playing the role of defends is the white blood cell. White blood
             cells also known as leukocytes are differ from red blood cells. It's fight
             infection, they are more largely and being lack hemoglobin. White blood
             cells are came from the stem cells in the red bone marrow. They defend us
             against pathogens that have invaded into our body. White blood cells are
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