From which among the following are blood clotting factors released?
- A.RBCs
- B.Eosinophils
- C.Platelets
- D.Monocytes
Correct answer
Explanation
The correct answer is C, Platelets. Platelets, or thrombocytes, release the factors that start blood clotting at a wound.
Platelets are tiny cell fragments made from large cells called megakaryocytes in the bone marrow; a healthy adult has about 1.5 to 4.5 lakh of them per cubic millimetre of blood. When a vessel is cut, they stick to the injured wall, form a plug and release substances such as thromboplastin. With calcium ions this sets off a chain in which prothrombin becomes thrombin, which turns soluble fibrinogen into a mesh of fibrin threads that traps blood cells and forms the clot. A fall in platelet count, as in dengue, can lead to bleeding.
A is wrong because red blood cells carry oxygen using haemoglobin and play no part in starting clotting. B is wrong because eosinophils are white blood cells that fight parasites and take part in allergic reactions. D is wrong because monocytes are white blood cells that become macrophages and engulf germs.
Exam tip: Clotting chain: platelets → thromboplastin → prothrombin to thrombin (Ca²⁺) → fibrinogen to fibrin.
Practice Questions
View allWhich one of the following features is an indication for modification of stem of a plant?
- A.Presence of 'eye' on potato
- B.'Scale' found in onion
- C.'Tendril' found in pea
- D.'Hair' present in carrot
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The eyes of a potato are nodes with buds, and only a stem bears nodes and buds, so they prove that the potato is a modified stem.
Read the full explanation →Which one of the following metals is used in the filaments of photo-electric cells that convert light energy into electric energy ?
- A.Tungsten
- B.Copper
- C.Rubidium
- D.Aluminium
Show answer
Rubidium, an alkali metal like caesium, gives off electrons easily when light falls on it, so it is used in photoelectric cells.
Read the full explanation →Tooth enamel is made up of which one of the following calcium compounds ?
- A.Calcium carbonate
- B.Calcium sulphate
- C.Calcium hydroxide
- D.Calcium phosphate
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Tooth enamel is made mainly of calcium phosphate in the form of a hard crystal called hydroxyapatite. Enamel is the hardest substance in the human body, harder even than bone.
Read the full explanation →Which one of the following viruses used to be responsible for highly infectious disease Smallpox ?
- A.Adenovirus
- B.Variola virus
- C.Aichi virus
- D.Coxsackie virus
Show answer
Smallpox was caused by the variola virus, a large DNA virus of the pox family that spread from person to person through the air.
Read the full explanation →After fertilization, the fruit and the seed are produced by
- A.ovule and ovary, respectively
- B.ovary and ovule, respectively
- C.ovary, no ovule required
- D.ovule, no ovary required
Show answer
After fertilisation the ovary of the flower grows into the fruit, and each ovule inside it develops into a seed.
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