Platelets are parts of the blood that help the blood clot. They are smaller than red or white blood cells. Platelets are a natural source of growth factors. They circulate in the blood of mammals and are involved in hemostasis, leading to the formation of blood clots. Platelets release thread-like fibers to form these clots. 

Blood clotting is the process by which blood changes from liquid to gel and stop bleeding. When the blood vessels get injured, platelets in blood produces prothrombin in the presence of vitamin K. The prothrombin then converts into the thrombin (active form) in the presence of thrombokinase and calcium ions. This thrombin then converts fibrinogen (inactive) into the fibrin (active). Fibrin thread then plugs the damaged part and appear like a clot. Thus, the correct answer is option A.

Platelet, also called thrombocyte, colourless, nonnucleated blood component that is important in the formation of blood clots (coagulation). Platelets are found only in the blood of mammals.

Only mammals have platelets, tiny cells without nuclei that are responsible for plugging the leaks in the blood vessels. Other animals use more conventional systems of hemostasis. Some marine invertebrates have a single type of blood cell, responsible for hemostasis, but also for other types of defences. Non-mammalian vertebrates have specialized nucleated thrombocytes to do the job.

Platelets are small, non-nucleated cells that are derived from megakaryocytes in the bone marrow. Platelets circulate in the blood, sense damage to a blood vessel and accumulate at these sites, where they initiate blood clotting. They are fragments of cytoplasm that are derived from the megakaryocytes of the bone marrow.

Only mammals have Platelets. Non-mammals possess thrombocytes which are nucleated cells which have been shown to have a haemostatic function paralleling that of mammalian platelets.

A megakaryocyte is a large bone marrow cell with a lobated nucleus responsible for the production of blood thrombocytes (platelets), which are necessary for normal blood clotting.

Platelets, also called thrombocytes, are blood cells whose function is to stop bleeding. The average life span of circulating platelets is 7 to 10 days.

Platelets, also called thrombocytes, are blood cells whose function is to stop bleeding. Platelets have no nucleus: they are fragments of cytoplasm, which are derived from the megakaryocytes of the bone marrow, and then enter the circulation. These unactivated platelets are biconvex discoid structures. They are smallest of the three major blood types. They make up a tiny portion of the blood volume.

Life span of platelets is 8 - 9 days. Platelets, also called thrombocytes, are blood cells, whose function is to stop bleeding. Platelets have no nucleus: they are fragments of cytoplasm, which are derived from the megakaryocytes of the bone marrow, and then enter the circulation. These unactivated platelets are biconvex discoid structures. Life span of individual platelets is controlled by the internal apoptotic regulating pathway. Old platelets are destroyed by phagocytosis in the spleen and liver.

Blood platelets are found in mammals. Platelets, also called thrombocytes, are blood cells, whose function is to stop bleeding. Platelets have no nucleus: they are fragments of cytoplasm, which are derived from the megakaryocytes of the bone marrow, and then enter the circulation. These unactivated platelets are biconvex discoid structures.

Megakaryocytes cells is thrombocyte producer. A megakaryocyte is a large bone marrow cell with a lobulated nucleus responsible for the production of blood thrombocytes, which are necessary for normal blood clotting. Megakaryocytes normally account for 1 out of 10,000 bone marrow cells but can increase in number nearly 10- fold during the course of certain diseases.

Platelets are a source of thromboplastin. Thromboplastin is a plasma protein aiding blood coagulation through catalyzing the conversion of prothrombin to thrombin. It is a complex enzyme that is found in the brain, lung, and other tissues and especially in blood platelets and that functions in the conversion of prothrombin to thrombin in the clotting of blood, called as thrombokinase.

Structure absent from fresh frozen blood plasma are platelets. Platelets have no nucleus: they are fragments of cytoplasm which are derived from the megakaryocytes. The main function of platelets is to contribute to hemostasis: the process of stopping bleeding at the site of interrupted endothelium. They gather at the site and unless the interruption is physically too large, they plug the hole. In the fresh frozen blood plasma, there will be an absence of blood cells. So, in frozen plasma platelets are also absent.

Platelet also known as thrombocyte is a colourless, nonnucleated blood cell that is important in the formation of blood clots (coagulation). Platelets are found only in the blood of mammals. Platelets are formed when cytoplasmic fragments of megakaryocytes, which are very large cells in the bone marrow, pinch off into the circulation as they age. They are stored in the spleen. Hence, option C is the correct answer. 

A megakaryocyte is a large bone marrow cell with a lobulated nucleus, responsible for the production of blood thrombocytes (platelets), which are necessary for normal blood clotting. Megakaryocytes normally account for 1 out of 10,000 bone marrow cells but can increase in number nearly 10-fold during the course of certain diseases.

Blood is living tissue which is made up of liquid and solids. The liquid part, called as plasma, is made of water, salts, and protein. Over half of your blood is plasma. The solid part of your blood contains red blood cells, white blood cells, and platelets. Red blood cells deliver oxygen from your lungs to your tissues and organs. White blood cells fight infection and are part of your body's defense system. Platelets help blood to clot when you have a cut or wound. Bone marrow, the spongy material inside your bones, makes new blood cells. Blood cells constantly die and your body makes new ones. Red blood cells live about 120 days, and platelets live about 6 days. Some white blood cells live less than a day, but others live much longer. 

An antibody is a large, Y-shaped protein produced by the plasma cells that is used by the immune system to identify and neutralize pathogens such as bacteria and viruses. The antibody recognizes a unique molecule of the harmful agent (antigen), via the variable region. They are not formed by the stem cells. All the other statements are correct.
Therefore, the correct answer is option B.

The blood clot formed inside the blood vessel is called as a thrombus. When this thrombus breaks and travels to different parts of the body, then it is called embolus. Agglutinin is responsible for the agglutination.

The platelets are formed by fragmenting from cells found in bone marrow called as megakaryocytes, and similar to red blood cells, they do not have a nucleus. The average lifespan of a platelet is normally just 5 to 9 days.  

Red blood cells or RBCs are the most common type of blood cell and contains hemoglobin, which is the principal means of delivering oxygen.
Lymphocyte is a type of white blood cell, that is important in the immune system.
Basophils are granulocytes i.e., they contain large cytoplasmic granules in the cell nucleus and it stores histamine (a vasodilator).
Thrombocyte is a platelet and is crucial for blood clotting.
Thus, the correct answer is option (C), 'Thrombocytes'.

Platelets or thrombocytes are cell fragments produced from megakaryocytes (special cells in the bone marrow). Formation of platelets by fragmentation of megakaryocytes in bone marrow is known as thrombopoiesis.

The blood cells are of three major types they are erythrocytes(RBC), leucocytes(WBC) and platelets. Platelets or thrombocytes are cell fragments produced from megakaryocytes (special cells in the bone marrow).Blood normally contains 1,500,00 - 3,500,00 platelets mm – 3. Platelets can release a variety of substances most of which are involved in the coagulation or clotting of blood.  Blood platelets are present in the blood of Mammals.

The blood cells are of three major types they are erythrocytes(RBC), leucocytes(WBC) and platelets. Platelets or thrombocytes are cell fragments produced from megakaryocytes (special cells in the bone marrow). Formation of platelets by fragmentation of megakaryocytes in bone marrow is known as thrombopoiesis. As blood platelets are cell fragments they do not have any nucleus i.e Denucleated.

Hemorrhagic Disorders Spontaneous or near spontaneous bleeding caused by a defect in clotting mechanisms (blood coagulation disorders) or another abnormality causing a structural flaw in the blood vessels. Platelets play an important role in blood clotting, so thrombocytopenia puts you at higher risk of bleeding. Any time your platelet count drops below 50,000 per mm3 you are considered to be at increased risk for bleeding.

Thrombocytes are pieces of very large cells in the bone marrow called megakaryocytes. They help form blood clots to slow or stop bleeding and to help wounds heal.

Thrombocytes are also called Platelets. They are the vital component of blood. It's basic function is to stop bleeding by clumping and clotting blood vessel injuries. Its main function is to contribute to hemostasis that is the process of stop bleeding by adhesion. Reduction in the number of platelets causes clotting disorder and thus loss of blood from the body.

Platelets are the colourless cell fragments present in the blood. They are involved in the clotting. In the absence of platelets, the process of clotting will be affected. If there will be any wound when platelets are absent, the animal will die by shredding of all the blood.

Monocytes are actively phagocytic and they take in the invading pathogen or cell through the method of phagocytosis.

Platelets are formed by the fragmentation of special cells named megakaryocytes in bone marrow cell so answer is option.        

A megakaryocyte is a large bone marrow cell with a lobulated nucleus, responsible for the production of blood thrombocytes (platelets), which are necessary for normal blood clotting. 

Critical count of platelet is 40, 000 / mm$^{3}$. Platelets, also called thrombocytes, are blood cells whose function is to stop bleeding. Platelets have no nucleus: they are fragments of cytoplasm, which are derived from the megakaryocytes of the bone marrow, and then enter the circulation. These unactivated platelets are biconvex discoid structures. The normal number of platelets in the blood is 150,000 - 400,000 platelets per microliter (mcL). A low platelet count is below 150,000. If the platelet count is below 50,000, the risk of bleeding is very high. So, it is called critical platelet count.

Platelets are the cells found in blood which helps in the clotting of the blood. The formation of platelets takes place in bone marrow from large bone marrow cells known as megakaryocytes. These cells after becoming mature enough, undergo the process of cell fragmentation to produce platelet cells. The hormone that help in platelet production is thrombopoietin. 

Platelets are the parts of the blood that help the blood clot. They are smaller than red or white blood cells. If the number of platelets is too low, excessive bleeding can occur. However, if the number of platelets is too high, blood clots can form thrombosis, which may obstruct blood vessels and result in such events as a stroke. 

Megakaryocyte is a large bone marrow cell which are responsible for the production of thrombocytes. Thrombocytes help in normal blood clotting.

(a) Leukopenia is the decrease in the white blood cell count in the cells. 

Prothrombin is a glycoprotein occurring in blood plasma and is an essential component of the blood-clotting mechanism. Prothrombin is transformed into thrombin by a clotting factor known as factor X or prothrombinase; thrombin then acts to transform fibrinogen, also present in plasma, into fibrin, which, in combination with platelets from the blood, forms a clot (coagulation). Under normal circumstances, prothrombin is changed into thrombin only when an injury occurs to the tissues or circulatory system or both; therefore, fibrin and blood clots are not formed except in response to bleeding. Hypoprothrombinemia, a deficiency in prothrombin, is characterized by a tendency to prolonged bleeding. It is usually associated with a lack of vitamin K, which is necessary for the synthesis of prothrombin in the liver cells.