Pharmacognosy and Natural Products
Pharmacognosy and natural products test crude drugs, their botanical sources, active constituents, identification tests, adulteration and cultivation. RRB questions often use scientific names and plant parts.
Core rules
- Secondary metabolites include alkaloids, glycosides, tannins, resins, volatile oils and gums. Alkaloids are basic nitrogen compounds; many give positive Dragendorff, Mayer or Wagner tests.
- Know source and part: Cinchona bark yields quinine; Atropa belladonna yields tropane alkaloids such as atropine; Digitalis purpurea leaf yields cardiac glycosides; Papaver somniferum yields morphine; Rauwolfia serpentina root yields reserpine; Senna leaf yields anthraquinone glycosides; Acacia yields gum arabic; agar comes from red algae such as Gelidium.
- Pharmacopoeial evaluation uses organoleptic, microscopic, physical, chemical and biological methods. Adulteration may be substitution, exhaustion or addition of foreign matter.
Worked example
A bitter bark powder gives red fluorescence with dilute sulfuric acid and yields a quinoline alkaloid. The source is Cinchona bark; the main alkaloid is quinine. The test and bitter taste support identity, but microscopic examination and assay are still needed for pharmacopoeial compliance.
Traps
Do not mix up leaf, root and bark drugs. Digitalis is not the same as digoxin tablets, and not every glycoside is cardiac. Scientific names change; use the official pharmacopoeial name. A positive alkaloid test does not identify a single alkaloid.