The relationship between oxygen levels and hemoglobin saturation is indicated by the oxygen-hemoglobin dissociation (saturation) curve at high partial pressures of O2 (above about 40 mm Hg), hemoglobin saturation remains rather high (typically about 75 - 80%). This rather flat section of the oxygen-hemoglobin dissociation curve is called the 'plateau'. 40 mm Hg is the typical partial pressure of oxygen in the cells of the body. Examination of the oxygen-hemoglobin dissociation curve reveals that, under resting conditions, only about 20 - 25% of hemoglobin molecules give up oxygen in the systemic capillaries. This is significant (in other words, the 'plateau' is significant) because it means that you have a substantial reserve of oxygen. In other words, if you become more active, & your cells need more oxygen, the blood (hemoglobin molecules) has lots of oxygen to provide When you do become more active, partial pressures of oxygen in your (active) cells may drop well below 40 mm Hg.

Thrombosis is the formation of a blood clot inside a blood vessel, obstructing the flow of the blood through the circulatory system.
Thrombocytes are also called 'platelets' and these are the blood cells, whose function is to stop bleeding.
Thrombin is the enzyme that converts fibrinogen to fibrin, and a reaction that leads to the formation of fibrin clot.
Thrombocytopenia is the disorder in which there is an abnormally low amount of platelets.
Thus, the correct answer is option (A).

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 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 also thrombokinase.

Vitamin K plays a key role in helping the blood clot, preventing excessive bleeding. Unlike many other vitamins, vitamin K is not typically used as a dietary supplement. Vitamin K is actually a group of compounds. The most important of these compounds appears to be vitamin K1 and vitamin K2

Ca${+2}$ is necessary for blood coagulation -

Acid citrate dextrose solution (anticoagulant citrate dextrose solution) is a solution of citric acid, sodium citrate and dextrose in water. It is mainly used as an anticoagulant to preserve blood specimens required for tissue typing because it removes the calcium ion which plays an important role in blood clotting reaction.

All of them are anticoagulant. 'Citrate' is in liquid form and is used for coagulation tests, as well as in blood transfusion bags. It binds with the calcium ion, preventing the coagulation proteins from using them and thus prevent blood from clotting and this can be reversed with the addition of calcium. It can be in the form of sodium citrate or acid-citrate-dextrose.
'Oxalate' is an anticoagulant, which has a mechanism similar to that of citrate. It is used in fluoride oxalate tubes, used to determine glucose and lactate levels.
'Dicoumarol' is a naturally occurring anticoagulant that functions as a functional vitamin K depleter. It is also used in biochemical experiments as an inhibitor of reductases.
'Heparin' is widely used anticoagulant. It works by activating antithrombin III, which blocks thrombin from clotting blood. It can be used in vivo as an injectable anticoagulant. It can also be used to form an inner anticoagulant surface on various experimental and medical devices such as test tubes and renal dialysis machines.

Blood serum is the component of blood that has neither a blood cell nor a clotting factor. Serum includes all proteins not used in blood clotting (coagulation) and all the electrolytes, antibodies, antigens, hormones, and any exogenous substances (e.g., drugs and microorganisms). Hence, serum does not clot. Thus, the correct answer is option A.

In blood, platelets produce thromboplastin only at the site of injury and not in the normal condition which initiates the process of blood clotting. There is an another factor or protein called fibrinogen. When it makes contact with oxygen, it polymerizes to fibrin wires, creating a heap of fibrin wires, in which the various blood cells get caught, thus clogging the wound. Because all the oxygen in the blood is already bound to haemoglobin (red cells), it can't interact with the fibrinogen, thus cannot create a clot. Thus, the correct answer is option C.

Coagulation (blood clotting) is a complex process that involves a positive feedback system. The factors involved are-
Factor I Fibrinogen
Factor II Prothrombin
Factor III Tissue Factor (Thromboplastin)
Factor IV Calcium
Factor V Labile factor, proaccelerin, Ac-globulin
Factor VII Stable factor, proconvertin
Factor VIII Antihaemophilic globulin (AHG), Antihaemphilic factor A 
Factor IX Christmas factor, plasma thromboplastin component
Factor X Stuart power factor
Factor XI Plasma thromboplastin antecedent
Factor XII Hageman factor
Factor XIII Fibrin stabilising factor
Vitamin K is essential for synthesis of factors II, VII, IX and X.
Their numbers represent the order in which they were discovered.

Clotting factor VIII is the antihemophilic factor while factor VII serves as an accelerator of serum prothrombin conversion. Clotting factor V is proaccelerin. Clotting factor VI was once considered to have clotting function but is now rejected. Thus, the correct answer is C. 

One of the initial steps in blood coagulation is the release of thromboplastin that interacts with other clotting factors and calcium ions. Fibrinogen is a soluble blood protein that becomes insoluble and forms fibrin strands during last steps of clotting. Bilirubin is the breakdown product of hemoglobin. Thus, the correct answer is C.

Heparin is a natural anticoagulant in the body. Hirudin is an anticoagulant produced by leech while sucking the blood of the host. EDTA acts as an anticoagulant by removing calcium ions from the blood and thus chelates with them.

Heparin is a natural anticoagulant produced in the liver and helps in checking the clotting of blood inside blood vessels. 

Blood clotting (coagulation) is the process by which blood vessels repair ruptures after injury. Calcium works together with vitamin K and a protein, called as fibrinogen in the clotting cascade, which forms fibrin. The fibrin hardens very quickly to form a scab over the wound. 

Prothrombin is a plasma protein which is converted into thrombin in the presence of thromboplastin released by platelets at the site of injury. The thrombin then converts protein fibrinogen into insoluble fibrin and thus aids in blood clotting. 

Coagulation (also known as clotting) is the process by which blood changes from a liquid to a gel, forming a clot. The activation of some of the enzymes in the coagulation cascade is dependent on vitamin K. In the presence of other plasma proteins (clotting factors) and calcium ions, this leads to the activation of a protein called as factor X. 

Vitamin K plays an important role in blood clotting. It is required by the body for the synthesis of prothrombin by the liver. Prothrombin is a plasma protein which gets converted into thrombin during the clotting process and thus helps in clotting mechanism. Thus, the correct answer is option B. 

Sodium oxalate (like citrates) can be used to remove calcium ions (Ca$^{2+}$) from the blood plasma. The oxalate prevents clotting by forming insoluble calcium salts, thus removing ionic calcium (or cations).
Therefore, the correct answer is option A.

Prothrombin is a plasma glycoprotein produced in the liver. It gets converted into thrombin by a clotting factor prothrombinase which further transforms fibrinogen into fibrin which combines with platelets to form clot. 

Blood clotting factors are needed for blood to clot (coagulation). Prothrombin, or factor II, is one of the clotting factors made by the liver. Vitamin K is needed to make prothrombin and other clotting factors. So, blood does not clot in the absence of Vitamin K because it is essential for the synthesis of prothrombin and not because it is an essential component of the clot, platelets or essential for fibrinogen. 

Platelets are tiny components in blood that initiate blood clots by releasing thromboplastin at the site of injury. Thromboplastin initiates the process of blood clotting. Thus, the correct answer is option C.

Heparin is a natural anticoagulant of the body produced in the liver. It is normally found circulating through the bloodstream. It prevents the blood clotting in veins and arteries during normal circulation.

• Haemophilia is a group of hereditary genetic disorders in which the body's blood clotting ability fails to stop bleeding if any cut happens.
• Thus, it is also known as bleeder's disease. One type of haemophilia called haemophilia A happens due to the deficiency of blood clotting factor VIII. 

In human, the prothrombin required for blood clotting is produced in the liver in the presence of vitamin K. It gets converted into thrombin in the presence of thromboplastin and thus forms an essential step in the clotting process. 

Coagulation or clotting is a process where the blood in liquid form turns into a gel. The mechanism involves activation, adhesion and aggregation of platelets and deposition of fibrinogen. Though this is an inactive clotting factor, it helps to clot by the formation of insoluble fibrin.

A blood clot that forms inside one of your veins or arteries is called a thrombus. A thrombus may also form in your heart. A thrombus that breaks loose and travels from one location in the body to another is called an embolus.

When a clot occurs in an undamaged blood vessel, It stops the flow of blood to the rest of the tissue beyond the clot as, the blood can't flow through the clot. It causes paralysis in most of the cases. 

Blood-clotting proteins circulate in the blood plasma in an inactive form, poised to participate in blood coagulation upon tissue injury. Blood-clotting proteins generate thrombin, an enzyme that converts fibrinogen to fibrin, and a reaction that leads to the formation of a fibrin clot.

Prothrombin is a coagulation or clotting factor that is needed for the normal clotting of blood. A cascade of biochemical events leads to the formation of the final clot. In this cascade, prothrombin is a precursor to thrombin.
Prothrombin is produced in the liver and is modified in the presence of vitamin K.
Therefore, the correct answer is option A.

Platelets are components of blood. They prevent bleeding by activating coagulation mechanisms hence contribute in wound healing. They play an important role in inflammatory and proliferative events. If the platelets are not present in the blood there will be continuous loss of blood by the blood vessels which may prove fatal.

Sodium oxalate acts as an anticoagulant. Sodium oxalate inhibits blood coagulation by forming an insoluble complex with calcium because calcium is a cofactor that involves in the clotting process. Hence, option A is the correct answer.

Fibrinogen is factor I and its source is liver. When fibrinogen is converted into fibrin by thrombin, it forms long strands, that compose the mesh network for clot formation.
Calcium is factor IV and its source is bone and absorption from food in gastrointestinal tract. It works with many clotting factors for activation of the other clotting factors.
Vitamin K is an essential factor to various protein enzymes, that are a part of coagulation cascade.
Vitamin D is found in fish and liver oil and is essential for absorption of calcium.
Thus, the correct answer is option B.

Coagulation is the process by which the blood changes from a liquid to a gel-like form. Blood plasma will coagulate, as, it has clotting factors in it and fibrinogen protein.
Serum will not coagulate, as, it do not have any clotting factors and fibrinogen.
Lymph is more like blood plasma, so, contains clotting factors and will coagulate.
Whole blood obviously coagulate for containing the same above factors.
Thus, the correct answer is option (B).

Factor VIII is an important blood clotting protein, which is also known as anti-haemophilic factor (AHF), encoded by the F$ _{8}$ gene.
Factor VIII circulates in the bloodstream in an inactive form, bound to another molecule, called Von Willebrand factor, until an injury that damages the blood vessels occurs. When injury occurs, the factor VIII is activated and separates from Von Willebrand factor. The active protein interacts with another coagulation factor, called factor IX. This interaction leads to a chain of additional reactions, that form a blood clot.

When there is an injury and blood is shed, the platelets disintegrate and liberate thromboplastin or factor III. Certain amount of thromboplastin is also derived from the damaged tissues of the injured locality.
Thromboplastin converts prothrombin into thrombin with the help of calcium ions and thrombin interacts with fibrinogen forming fibrin. This is clot.
Calcium is the Factor IV and it acts as a co-factor in the coagulation process.
Thus, the correct answer is option (B).

The presence of calcium and other clotting factors, Factor X activates an enzyme called prothrombin activator. The enzyme prothrombin activator then converts plasma protein prothrombin into thrombin. Thrombin is the enzyme which in turn converts fibrinogen into fibrin. Polymerized fibrin together with platelets(corpuscles) forms a clot at the wound site. Hence blood clot is mainly due to fibrin and corpuscles.

The mechanism of blood clotting involves the presence of calcium and other clotting factors, Factor X activates an enzyme called prothrombin activator. The enzyme prothrombin activator then converts plasma protein prothrombin into thrombin. Thrombin is the enzyme which in turn converts fibrinogen into fibrin. Polymerized fibrin together with platelets forms a clot at the wound site. The prothrombin is a plasma protein synthesized in the liver. Vitamin K is essential for the synthesis of prothrombin.

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 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 also thrombokinase.

Fibrinolysis is a process that prevents blood clots from growing and becoming problematic. This process has two types: primary fibrinolysis and secondary fibrinolysis. The primary type is a normal body process, whereas secondary fibrinolysis is the breakdown of clots due to a medicine, a medical disorder, or some other causes. In fibrinolysis, a fibrin clot, the product of coagulation, is broken down. Its main enzyme plasmin cuts the fibrin mesh at various places, leading to the production of circulating fragments that are cleared by other proteases or by the kidney and liver. Hence Enzyme causing lysis of fibrin during fibrinolysis is plasmin.

So, the correct answer is 'Plasmin'.

Thrombokinase is also known as thromboplastin. It is a complex enzyme which aids in clotting of blood. It is present in platelets and some body tissues. When the platelets aggregate at the site of injury, thrombokinase is released from platelets and damaged tissues. Thrombokinase converts prothrombin into thrombin which acts as an enzyme and converts fibrinogen into fibrin threads. The fibrin threads form a clot at the site of injury. Hence thrombokinase is produced in blood clotting.

• Whenever there is rupture of blood vessels or damage is caused to blood, a complex of substances called prothrombin activator complex is formed. 
• The activators convert prothrombin into thrombin.
• Thrombin acts as an enzyme and converts fibrinogen into fibrin threads.
• Fibrin threads accumulate and clump to form blood clot at the wound site.

Thrombokinase is a substance present in platelets which are necessary for coagulation of blood. Thromboplastin helps in the conversion of prothrombin to thrombin in the presence of calcium which is the vital step in coagulation of blood.

Vitamin K helps in the synthesis of prothrombin in the liver.

In the blood coagulation pathway thrombin activates Factor XIII to XIIIa that helps in binding of fibrin monomers to form the stable fibrin filament.

Plasmin is the proteolytic enzyme that induces lysis of fibrin to fibrin degradation products during fibrinolysis (enzymatic breakdown of fibrin during blood clots)

Calcium ions and platelets are essential factors for clotting of blood. During some injury, the platelets release inactivated platelet factors that are involved in the activation of other factors involved in the formation of clots in the blood. Calcium ions in the blood catalyze the activation of many factors involved in clot formation like factor VIII, factor IX, factor V and factor XIII.

Thus, the correct answer is 'Calcium ions and platelet factors.'

There are two processes that can initiate clotting

Clotting requires calcium ions ($Ca2^+$), which is why blood banks use a chelating agent to bind the calcium in donated blood, so the blood will not clot in the bag.

All the reactions which happen during the clotting process require calcium ions for their occurrence. Calcium works together with vitamin K and a protein called as fibrinogen in the clotting cascade. Without adequate levels of calcium and vitamin K, blood will take longer to clot and if both nutrients are missing it could be fatal. Therefore, the correct answer is option C.

Prothrombin is a precursor of the clotting factor thrombin. Prothrombin forms thrombin in the cascade clotting reaction. It is produced in the liver cells in the presence of vitamin K.

The Hageman factor XII is activated when it comes in contact with a damaged blood vessel. The activated Hageman factor activates the factor XI. The activated factor XI acts on Chrishmas factor IX to form activated IXa. Factor IXa combines with AHG VIII phospholipid and calcium ions to form a complex called intrinsic factor X activator complex. Thus the correct answer is option A.

The following enzymes are involved in the mechanism of blood clotting in human.

The liquid part of coagulated blood is known as serum. It is the liquid portion of blood clot . It includes all proteins not used in clotting of blood and all the electrolytes, hormones, antibodies, antigens etc..

Blood coagulation is a complex biochemical process involving platelets and many proteins (enzymes).  Calcium is involved at several steps in the blood clotting, including the activation of the platelets, activation of clotting factors and enzymes which are present in the blood in inactive form. The $Ca^{++}$ ions bind with prothrombin and covert it into active form thrombin. The thrombin in turn converts fibrinogen into fibrin (a thread like protein) which traps red blood cells and helps in the formation of clot.

Sodium oxalate, like citrates, can be used to remove calcium ions (Ca${^2}$${^+}$) from blood plasma. It thus prevents blood from clotting. In the presence of calcium ions and other clotting factors, factor X activates an enzyme called prothrombin activator. This enzyme then converts the plasma protein prothrombin into thrombin. Thrombin is an enzyme that, in turn, converts fibrinogen to fibrin.