In the process of blood clotting, the enzyme 'thrombin' is formed from its inactive precursor 'prothrombin' in the presence of: MCQ with Answer and Explanation

Question

In the process of blood clotting, the enzyme 'thrombin' is formed from its inactive precursor 'prothrombin' in the presence of:

A. Heparin and potassium

B. Thromboplastin and calcium ions

C. Fibrinogen and calcium

D. Plasmin and sodium

Answer: Option B

Solution (By JKSSB Mock Tests)

Blood clotting (coagulation) is a cascade of enzymatic reactions. When tissue is damaged, it releases thromboplastin (tissue factor). In the presence of calcium ions (Ca2+), thromboplastin activates the conversion of the inactive plasma protein prothrombin (synthesized in the liver with the help of Vitamin K) into the active enzyme thrombin. Thrombin then catalyzes the conversion of soluble fibrinogen into insoluble fibrin threads, forming the clot mesh.

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The structure that prevents backflow of blood from the left ventricle to the left atrium is the:

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Correct Answer: Option A

Explanation:
The bicuspid (mitral) valve has two cusps and closes during ventricular systole to prevent regurgitation into the left atrium. The tricuspid valve is on the right.

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Correct Answer: Option C

Explanation:
Excretion is the elimination of nitrogenous waste products (urea, uric acid, ammonia) and other metabolic wastes from the body, primarily by the kidneys. Digestion is breakdown of food, circulation is transport, respiration is gas exchange and energy release. Excretion maintains homeostasis of body fluids and prevents toxic accumulation.

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In the five-kingdom classification, bacteria are placed in the kingdom:

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Correct Answer: Option C

Explanation:
R.H. Whittaker's five-kingdom classification (1969) categorizes organisms into Monera, Protista, Fungi, Plantae, and Animalia. Monera includes all prokaryotes—bacteria, cyanobacteria, and archaebacteria—characterized by lack of true nucleus and membrane-bound organelles. Protista includes unicellular eukaryotes. Fungi are multicellular saprophytes. Plantae are autotrophic eukaryotes. Monera is the only kingdom of prokaryotes in this system.

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