(a) They protect the body from environmental allergens.
(b) They alleviate the body’s pain and inflammation
(c) They act as immunosuppressants in the body.
(d) They protect the body from the diseases caused by pathogens.

Ans: d

Explanation:

Blood Basics

Blood is a specialized body fluid. It has four main components: plasma, red blood cells, white blood cells, and platelets.  

                                              Components of blood 

The Components of Blood and Their Importance

1. Plasma

The liquid component of blood is called plasma, a mixture of water, sugar, fat, protein, and salts. The main job of the plasma is to transport blood cells throughout your body along with nutrients, waste products, antibodies, clotting proteins, chemical messengers such as hormones, and proteins that help maintain the body’s fluid balance. 

2. Red Blood Cells (also called erythrocytes or RBCs)

Known for their bright red color, red cells are the most abundant cell in the blood, accounting for about 40 to 45 percent of its volume. 

Production of red blood cells is controlled by erythropoietin, a hormone produced primarily by the kidneys.

 Red blood cells start as immature cells in the bone marrow and after approximately seven days of maturation are released into the bloodstream. The red blood cell survives on average only 120 days.

Red cells contain a special protein called hemoglobin, which helps carry oxygen from the lungs to the rest of the body and then returns carbon dioxide from the body to the lungs so it can be exhaled. Blood appears red because of the large number of red blood cells, which get their color from the hemoglobin. 

3. White Blood Cells (also called leukocytes)

White blood cells protect the body from infection. They are much fewer in number than red blood cells, accounting for about 1 percent of blood.

There are different types of white blood cells

a. Lymphocyte :The other major type of white blood cell is a lymphocyte. Lymphocytes make antibodies to fight infection. They are found in the lymph nodes, thymus, spleen, tonsils, adenoids and bone marrow. They are also found in lymphatic tissue in other parts of the body, such as the appendix, the small intestine and other parts of the digestive system and respiratory system.

 There are two main populations of these cells. 

T lymphocytes help regulate the function of other immune cells and directly attack various infected cells and tumors.

B lymphocytes make antibodies, which are proteins that specifically target bacteria, viruses, and other foreign materials.

b. Granulocytes :Granulocytes fight infection and become active in response to tissue inflammation. 

The 3 main types of granulocytes are: Neutrophils , Eosinophils and Basophils

Neutrophils : The most common type of white blood cell is the neutrophil, which is the “immediate response” cell and accounts for 55 to 70 percent of the total white blood cell count.

Each neutrophil lives less than a day, so bone marrow must constantly make new neutrophils to maintain protection against infection. 

Eosinophils and Basophils, which attack and destroy certain parasites and are activated during an allergic reaction 

c. Monocytes  : Monocytes help fight infection by changing into cells called macrophages, which eat foreign invaders, such as bacteria and waste from dying cells.

4. Platelets (also called thrombocytes)

Unlike red and white blood cells, platelets are not actually cells but rather small fragments of cells. Platelets help the blood clotting process (or coagulation) by gathering at the site of an injury, sticking to the lining of the injured blood vessel, and forming a platform on which blood coagulation can occur. 

A higher than normal number of platelets can cause unnecessary clotting, which can lead to strokes and heart attacks , Conversely, lower than normal counts can lead to extensive bleeding.

Where Do Blood Cells Come From?

Blood cells develop from hematopoietic stem cells and are formed in the bone marrow through the highly regulated process of hematopoiesis. Hematopoietic stem cells are capable of transforming into red blood cells, white blood cells, and platelets. 

Stem cells are found in the bone marrow, blood and umbilical cord blood. Stem cells develop into blood cells in the bone marrow. When blood cells are mature and able to function, they leave the bone marrow and move into the blood.

Most stem cells are found in the bone marrow. Stem cells can also be found in smaller amounts in the bloodstream. These are called peripheral blood stem cells. Umbilical cord blood also has stem cells but there are fewer stem cells than those in the bone marrow and blood.

These stem cells can be found circulating in the blood and bone marrow in people of all ages, as well as in the umbilical cords of newborn babies. Stem cells from all three sources may be used to treat a variety of diseases, including leukemia, lymphoma, bone marrow failure, and various immune disorders. 

Hence, option d is correct.

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