Blood

Circulatory system

Blood circulatory system plays an important role in the body of organisms. Essential nutrient and useful materials need to be transported from one part of the body to the other part of the body. The blood transport these essential nutrients, oxygen and hormones to the different tissues of the body and also transport unwanted and harmful substances produced in the body to the excretory organs. This process continues in the body and is called transportation or circulatory system. In unicellular and simple organisms, the transport system is simple while, in complex organisms, the transport system is well developed. In developed organisms, blood is flowing all the time in blood vessels. So, essential nutrients are carried by the blood to different part of the body and unwanted substances are carried by the blood from tissue to the excretory organs.

Blood

Blood is a red fluid which circulates around the body through blood vessels. Blood is red due to the iron-containing pigments called hemoglobin.Hemoglobin is made up of two parts; heme- iron containing part and glopin- protein part. Blood is composed of plasma and blood cells. Plasma is a yellowish transparent liquid. It contains 90% water and 10%nutritive substances dissolved in water. It also carries the carbon dioxide gas produced during respiration by the lungs. It helps to carry urea from the liver to the kidneys and hormones secreted by the endocrine glands to the tissues.

Blood Cell

There are three types of blood cells in the blood i.e. red blood cells, white blood cells, and platelets. Red blood cells are many in number in the blood. These blood cells are very small and have no nucleus. They are made in bone marrow and destroyed in the spleen. Hemoglobin present in cells absorbs oxygen from the lungs and helps to transport to the different cells of the body. The decrease in the number of red blood cells in the blood causes anemia.

White blood cells are bigger than red blood cells and are less in number in the blood. These cells are of various types and colorless. They have the distinct nucleus but have no fixed shape. They are also made in bone marrow. These cells fight against germs in an infected area and protect the body from disease. Some of them destroy the disease-causing microbes while some of them remove the destroyed cells or microbes from the infected area and help to heal the wounds.

Platelets are very tiny cells. These are smaller than both red blood cells and white blood cells. They are also of various kinds. They are less in number in the blood. They are spherical in shape and have no nucleus. They are also made in bone marrow, they help in clotting of blood at wounds and damaged skin or cut. Thus, platelets play an important role to clot the blood in wounds or cuts.

Things to remember

• Blood is a red fluid which circulates round the body through blood vessels. Blood is red due to the iron containing pigments called hemoglobin. Blood is composed of plasma and blood cells. Plasma is a yellowish transparent liquid.
• There are three types of blood cells in the blood i.e. red blood cells, white blood cells and platelets.
• White blood cells are bigger than red blood cells and are less in number in the blood. 
• There are three types of blood cells in the blood i.e. red blood cells, white blood cells, and platelets. 
• Blood is a red fluid which circulates around the body through blood vessels. 

• It includes every relationship which established among the people.
• There can be more than one community in a society. Community smaller than society.
• It is a network of social relationships which cannot see or touched.
• common interests and common objectives are not necessary for society.

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