GPAT practice: Pharmacognosy
20 original GPAT-style questions on pharmacognosy: crude drug classification, constituents and tests, adulteration, evaluation and biological sources, with answers and explanations. Tap an option to check your answer, or open "Show answer".
1. Arranging crude drugs according to their active constituents (alkaloids, glycosides, tannins, volatile oils and so on) is called which type of classification?
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Answer: B — Chemical classification groups drugs by the main class of active constituent. Morphological classification uses the part of the plant (leaf, bark, root), and taxonomical classification uses the plant's botanical family and genus.
2. Quinine, used in the treatment of malaria, is obtained from the bark of which genus?
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Answer: C — Cinchona bark (Cinchona officinalis and related species, family Rubiaceae) contains quinoline alkaloids such as quinine and quinidine. Rauwolfia yields reserpine and Atropa yields atropine.
3. Which of the following is the commercial source of digoxin?
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Answer: A — Digoxin is a cardiac glycoside obtained from the leaves of Digitalis lanata. Strophanthus kombe gives k-strophanthoside, so it is a tempting but different cardiac glycoside source.
4. A brown ring forms at the junction of two layers when a plant extract in glacial acetic acid containing a trace of ferric chloride is underlaid with concentrated sulphuric acid. Which test is this, and what does it detect?
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Answer: D — The Keller-Killiani test detects 2-deoxy sugars (such as digitoxose) in cardiac glycosides and gives a brown ring at the interface. Legal's test also detects cardiac glycosides but depends on the unsaturated lactone ring and uses sodium nitroprusside, giving a red colour.
5. Which reagent gives an orange-red precipitate with alkaloids?
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Answer: A — Dragendorff's reagent (potassium bismuth iodide) precipitates most alkaloids as orange-red complexes. Fehling's solution detects reducing sugars, Molisch's detects carbohydrates, and Millon's detects tyrosine-containing proteins.
6. In Borntrager's test, the ammoniacal layer turns pink to red when the extract contains:
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Answer: A — The test is used for anthraquinone derivatives such as those in senna, aloe and rhubarb. O-glycosides must first be hydrolysed (and oxidised) to the free anthraquinone before the pink-red colour appears in the alkaline layer.
7. Which colour is obtained when ferric chloride solution is added to a hydrolysable (gallotannin type) tannin?
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Answer: C — Hydrolysable tannins, which are esters of gallic or ellagic acid with a sugar, give a blue-black colour with ferric chloride. Condensed (catechol type) tannins give a green or brownish-green colour.
8. Cutch (catechu) is the dried extract from the heartwood of which plant?
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Answer: B — Black catechu is prepared from the heartwood of Acacia catechu and is rich in condensed tannins (catechin and catechutannic acid). Terminalia chebula and Quercus infectoria (galls) are mainly hydrolysable-tannin drugs.
9. What is the major chemical constituent of clove oil, which is obtained from dried flower buds of Syzygium aromaticum (Myrtaceae)?
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Answer: D — Clove oil is mostly eugenol, a phenolic compound. Cinnamaldehyde is the main constituent of cinnamon bark oil, menthol of peppermint oil and thymol of ajowan oil.
10. Which method is most suitable for obtaining the fragrance of delicate flowers such as jasmine that are easily damaged by heat?
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Answer: C — Enfleurage extracts the fragrance into a cold fat and avoids heat, so it suits delicate flowers. Steam distillation and hydrodistillation use heat; expression is used for citrus peel oils such as lemon and orange.
11. The stomatal index of a leaf drug is calculated as:
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Answer: D — Stomatal index = S / (E + S) x 100, where S is the number of stomata and E the number of ordinary epidermal cells in the same area. Unlike stomatal number, the index is fairly constant for a species and is a useful diagnostic feature.
12. The number of vein islets per square millimetre of leaf surface is called:
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Answer: C — The vein islet number is the average count of vein islets (small areas of photosynthetic tissue bounded by veinlets) per square millimetre. The vein termination number counts veinlet terminations per square millimetre, so it is a different measure.
13. Mixing exhausted ginger (from which the oleoresin has already been extracted) into genuine ginger powder is an example of:
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Answer: B — Mixing in drug material whose active principles have already been extracted lowers the quality while the powder still looks genuine; this is adulteration with exhausted drug. Substitution means replacing the drug with a different, usually inferior, species.
14. The foaming index is used to evaluate crude drugs rich in which constituent?
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Answer: B — Saponins form a stable persistent froth when shaken with water; the foaming index quantifies this property. Tannins are assessed by other methods, such as the hide-powder method.
15. Opium is the dried latex obtained by incising the unripe capsules of which plant?
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Answer: A — Opium comes from Papaver somniferum (Papaveraceae) and contains morphine, codeine, thebaine, papaverine and noscapine. Papaver rhoeas (corn poppy) does not contain morphine in useful amounts.
16. Sennosides A and B, the active principles of senna, are best classified as:
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Answer: D — Sennosides are dianthrone O-glycosides from the leaves and pods of Cassia angustifolia (Senna alexandrina). Colonic bacteria release the active aglycone, producing the laxative effect.
17. Ephedrine from Ephedra species is called a protoalkaloid (amino-alkaloid) because:
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Answer: A — Protoalkaloids are amines derived from amino acids in which the nitrogen is outside any ring system, as in ephedrine (from phenylalanine). True alkaloids have the nitrogen in a heterocycle.
18. The colouring principle crocin is found in which drug?
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Answer: B — Saffron consists of the dried stigmas (with tops of the styles) of Crocus sativus (Iridaceae); its colour is due to crocin and its bitter taste to picrocrocin. Turmeric is coloured by curcumin.
19. Which statement about Aloe (dried juice of leaves of Aloe barbadensis) is correct?
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Answer: A — Aloe contains barbaloin (aloin), an anthrone C-glycoside, which is responsible for its purgative action. It contains no cardiac glycosides, tropane alkaloids or significant volatile oil.
20. Cinnamon bark oil is characterised by which main constituent, and the bark is obtained from which species?
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Answer: B — True (Ceylon) cinnamon is the dried inner bark of Cinnamomum zeylanicum (Lauraceae) and its oil is rich in cinnamaldehyde. Eugenol is the main component of clove oil, and citral belongs to lemongrass oil.