Question

Assertion: Fibrins are formed by the conversion of inactive fibrinogens in the plasma by the enzyme thrombin.
Reason: Plasma without fibrinogen and blood corpuscles is called serum.
(a) Both assertion and reason are correct and the reason is the correct explanation for assertion
(b) Both assertion and reason are correct but the reason is not the correct explanation for assertion
(c) Assertion is correct but the reason is incorrect
(d) Both assertion and reason are incorrect

Answer 1

Hint: During a minor injury, blood starts to clot after some time which is mainly due to the formation of fibrin clots. This stage also represents the final stage after blood coagulation and is resistant to lysis.

Complete answer:
To answer this question we first need to know basic information about fibrins and serum.
Fibrin is known to be a major component of blood clotting and is typically an insoluble protein produced in response to any bleeding in the body. It is also very tough and is arranged in long fibrous chains. These chains are in turn formed from fibrinogen which is a soluble protein and is found in blood plasma. At the site of injury or bleeding, fibrinogen gets converted into fibrin by the action of an enzyme called thrombin which is a clotting enzyme.
Long fibrin threads are formed as fibrin molecules combine together. These long threads also entangle platelets to together form a spongy mass that hardens after a short period of time. This hardening process is governed by a substance known as fibrin stabilizing factor.
Serum on the other hand does not play any part in clotting and is a fluid and is one of the soluble components of blood. It can be better understood as blood plasma without fibrinogens. Serum includes electrolytes, various types of proteins, antibodies, antigens, hormones, and other exogenous substances. In total the serum does not contain WBC(leucocytes), RBC(erythrocytes), platelets, or clotting factors and can be seen as a yellow liquid that generally oozes from a clotted wound.

Additional information:
Following are the steps to separate serum from blood:
-Collect blood samples in a test tube.
-Allow the blood to clot by leaving it undisturbed for 15-30 minutes at room temperature
- Remove the clot by centrifuging the sample for 10 minutes
-The resulting supernatant is the serum which is removed by Pasteur pipette.
Following are the steps to separate plasma from blood:
-Collect blood sample in anticoagulant treated tubes like EDTA treated or citrate treated
-Cells are removed from the plasma by centrifugation
-The supernatant is the plasma which is removed by Pasteur pipette. The same is depicted in the image below.

So, the correct answer is option b ‘both assertion and reason are correct but the reason is not the correct explanation for assertion’

Note:
Fibrinogen plays many crucial roles in physiological processes. In addition to this the formation of a stable blood clot, containing polymerized and cross-linked fibrin or fibers, is crucial to prevent excess blood loss from the body and continue wound healing upon vascular injury.