Picture the moment that decides your PCG 212 mark: a demonstrator slides an unlabelled powder or a bare leaf across the bench and asks you to name the plant. No options, no hints. You confirm it the way pharmacognosists actually do, by reading the diagnostic characters the specimen carries: the shape of its starch grains, whether its surface is covered in hairs, the type of stomata on its epidermis, the crystals sitting in its tissue. That habit of proving identity from evidence, not memory, is the whole skill this practical trains. This page is a student-written study companion for PCG 212 – Pharmacognosy Practical I, the second-semester laboratory course for 200 Level Pharmacy students.
The reason PCG 212 is so scoreable is that the answers are physical and repeatable. A 70% sulphuric acid test either dissolves a fibre completely or it does not; acacia dissolves in water while tragacanth only swells; potato starch grains are large and oval while maize grains are small and angular. Learn what each result means and you can reproduce it under pressure. The summaries below turn the practical schedules into plain notes, covering the microscope and micrometry, specimen preparation, diagnostic plant structures, macroscopy of crude drugs, starches and gums, and mineral matters, with original practice questions and worked answers so you can check that each idea has stuck. The complete workbook sits in the reader at the end of this page as a free bonus to the notes here.
- Course: PCG 212 – Pharmacognosy Practical I
- College / Department: College of Pharmacy – Department of Pharmacognosy
- Level / Semester: 200 Level, Second Semester
- Topics covered: The microscope & micrometry, practical techniques (clearing agents, stains, sections, maceration), diagnostic plant structures (stomata, trichomes, crystals), macroscopy of crude vegetable drugs, starches & gums (Schedules II and III), fibres & surgical dressings, and mineral matters (Schedule IV)
- Best for: Continuous assessment + final exam revision
Topics Covered in PCG 212 – Pharmacognosy Practical I
1. The Microscope and Micrometry
Almost every mark in this practical starts at the microscope, so know its parts and its rules cold. Carry it with one hand on the arm and the other under the base, always begin viewing on low power, and focus by raising the stage with the coarse knob then sharpening with the fine knob. Treat the optics gently: no fingers on the lenses, no alcohol (it dissolves the cement holding them), and lens tissue only. Micrometry then lets you measure what you see, which matters because a genuine drug and an adulterant can share the same tissues yet differ in cell size. You calibrate a graticule against a stage micrometer, where each small stage division equals 10 µm. Exam tip: practise the calibration sum until it is automatic, since a single worked figure like 1000 ÷ 75 = 13.3 µm per division is the kind of answer examiners can mark in seconds.
2. Practical Techniques: Clearing, Staining and Sectioning
Before a tissue reveals anything useful it usually has to be cleared of pigment, stained, and cut thin. Chloral hydrate is the workhorse clearing agent: it strips out chlorophyll, starch, proteins, and mucilage and restores the shape of cells in dried material, though it leaves calcium oxalate and oils alone. Stains then target specific features. Phloroglucinol with HCl turns lignified walls red, iodine stains starch blue-black, and ruthenium red picks out gums and mucilages. You cut a transverse section (T.S.) across the organ or a longitudinal section (L.S.) along it, then mount in dilute glycerin under a coverslip lowered slowly to avoid air bubbles. Maceration methods such as the Schultz technique separate lignified elements, and all of it belongs in a fume cupboard. Exam tip: tie each reagent to one colour outcome, because reagent-to-result matching is a fast, high-frequency question type here.
3. Diagnostic Structures: Stomata, Trichomes and Crystals
Diagnostic characters are the distinguishing features that confirm a drug is the right plant, and three of them do most of the work. Stomata come in four named patterns: anomocytic (a stoma ringed by ordinary-looking cells, as in Digitalis), anisocytic (three or four subsidiary cells, one smaller), paracytic (subsidiary cells parallel to the pore), and diacytic (two cells meeting at right angles). Trichomes, the epidermal hairs, may be glandular or non-glandular and are strongly species-specific. Calcium oxalate crystals take recognisable forms too: needle-like raphides, single prismatic crystals, or cluster-shaped druses. Read together, these features fingerprint a species. Exam tip: anchor each stoma and crystal type to a named plant from your slides, so a naming question becomes recall of a pair rather than a guess.
4. Macroscopy of Crude Vegetable Drugs
Macroscopy identifies a crude drug from its outside alone, using shape, size, colour, texture, odour, taste, and surface features. It is the quickest check and your first defence against adulteration. For every specimen you record a fixed set of details: common and botanical name, family, the morphological part, the form (whole, powder, or tincture), the major constituents, a plain unshaded sketch, and your observations. The workbook drills this on real samples, from the kidney-shaped seed of Phaseolus vulgaris to the orange rhizome of Curcuma longa, whose curcumin gives turmeric both its colour and its anti-inflammatory action. Pairs such as pawpaw and okra sharpen the eye for placentation and seed structure. Exam tip: lock in the botanical name and family for each specimen first, because those two facts usually open the marks before any description does.
5. Starches and Gums (Schedules II and III)
Starches are polysaccharides that yield only glucose on full hydrolysis and are used as diluents, disintegrants, binders, and even as an antidote in iodine poisoning. All of them stay insoluble in cold water, gelatinise in hot water, and give a blue-black iodine reaction, so those tests will not separate them. What does separate them is granule shape and hilum: potato grains are large and oval with an eccentric hilum, maize grains are small and angular with a central dot, and wheat is a round mixture of large and small. Gums are unorganised drugs with no cellular structure. The classic distinction is acacia against tragacanth: acacia dissolves fully in water and gives a dark purple with iodine, while tragacanth only swells and turns golden brown. Exam tip: when a question asks you to tell two starches or two gums apart, lead with the feature that differs, not the shared blue-black or lead-acetate result everyone writes.
6. Mineral Matters (Schedule IV)
Four mineral drugs recur in this practical, and their sedimentation behaviour is the fastest way to tell them apart. Kaolin, a hydrated aluminium silicate, settles at a moderate rate without swelling and works as an adsorbent for gut toxins. Bentonite barely settles at all; it swells 12 to 15 times into a gel and suspends insoluble powders in lotions such as calamine. Chalk, prepared calcium carbonate, settles quickly and shows fossilised Foraminifera shells under cresol, and it serves as an antacid. Talc, purified magnesium silicate, is intensely slippery, floats before slowly settling, and acts as a glidant and lubricant in tablets. Exam tip: memorise the one-line sedimentation signature of each, since "which settles, which swells, which floats" is a reliable discriminator the examiner can ask in a single sentence.
Sample Practice Questions (With Answers)
Here are a few representative questions, written in our own words, with the reasoning explained so you understand the why, not just the result:
Q1. Under low power, 75 small graticule divisions line up exactly with 100 small stage-micrometer divisions. If one stage division equals 10 µm, what is the value of one graticule division?
Answer: First convert the stage reading: 100 stage divisions × 10 µm = 1000 µm (which is 1 mm). Those 1000 µm are covered by 75 graticule divisions, so one graticule division = 1000 ÷ 75 = 13.3 µm. This calibration is what lets you measure a particle later and catch an adulterant whose cells are the wrong size.
Q2. How would you distinguish acacia gum from tragacanth in the laboratory?
Answer: Use three points. Solubility: acacia dissolves readily in water to a viscous solution, while tragacanth only swells into a gel and never fully dissolves. Iodine (N/50): acacia turns dark purple, tragacanth turns golden brown. Ferric chloride (10%): tragacanth gives a deep yellow precipitate, whereas acacia shows no reaction, confirming tannins are absent. Both stay insoluble in alcohol and both give a white precipitate with lead acetate, so those two shared results cannot separate them.
Q3. Maize, potato, and wheat starch all give the same iodine reaction. How do you tell them apart microscopically?
Answer: All three stain blue-black with iodine, so identity rests on granule shape and hilum. Maize grains are small, angular or polygonal, with a central dot hilum. Potato grains are large and oval (the biggest of the three) with a distinct eccentric hilum. Wheat is a mixture of large and small round grains with an eccentric hilum. Shape and hilum position, not the colour test, are what expose an adulterated starch.
Q4. A surgical dressing shows no change in dilute sulphuric acid, gradual thinning in 50% acid, and complete dissolution in 70% acid. What does this tell you, and why?
Answer: The graded response identifies the fibre as pure cellulose. Dilute acid does nothing because cellulose is chemically stable under mild conditions; 50% acid partly degrades it; and 70% acid hydrolyses it completely. Complete dissolution in strong sulphuric acid is the confirmatory result for a purely cellulosic dressing such as absorbent cotton wool or gauze.
Q5. Tithonia diversifolia and Talinum triangulare are given to you as dried powders. What single microscopic feature most reliably separates them, and what supports it?
Answer: Trichomes. Tithonia carries numerous uniseriate, multicellular hairs, while Talinum has essentially none, so hair presence alone separates the powders. Supporting characters back it up: Tithonia shows anomocytic stomata and prismatic calcium oxalate crystals with a thick cuticle, whereas Talinum shows paracytic stomata, needle-like raphide crystals, and mucilage cells typical of a succulent. Once dried and powdered, these microscopic characters are the only reliable guard against substitution.
How to Study PCG 212 Effectively
- Split the syllabus into organised drugs (with a definite cellular structure) and unorganised ones (gums, resins, minerals, no cellular structure), because that single divide organises half the course.
- Build a reagent-to-result table you can reproduce from memory: iodine gives blue-black for starch, phloroglucinol plus HCl reds lignin, 70% sulphuric acid fully dissolves cellulose, ruthenium red marks gums.
- Pair every diagnostic feature with a named plant from your slides, for example paracytic stomata with Talinum and Vernonia, raphide crystals with Talinum, prismatic crystals with Tithonia.
- Rehearse the micrometry calibration until the arithmetic is instant, and be ready to state that each small stage division equals 10 µm.
- Memorise the botanical name and family for each macroscopy specimen first, then add the constituents, since names open the marks.
- Read the topic summaries here to build your foundation, then work through the full workbook in the reader below and attempt the practice questions from memory before the MCU test.
Download the Full PCG 212 Practice Workbook
The notes above stand on their own, but if you want the complete second-semester practical in one place, the full PCG 212 – Pharmacognosy Practical I workbook is loaded in the reader just below, with the full results tables for starches, gums, fibres, and mineral matters, plus the diagnostic character sheets for each plant. Read it right here on the page, or save a copy so you can keep drilling the reagent tests and specimen sketches offline in the days before your practical.
Frequently Asked Questions
Is this PCG 212 material free?
Yes, completely. There is no fee, sign-up, or paywall anywhere on this page. The PCG 212 notes, practice questions, and the downloadable workbook are open to any Pharmacy student who needs a hand with the practical.
Do I need to memorise every reagent colour, or is understanding enough?
You need both, because the colour is often the answer and the reasoning earns the rest of the marks. Learn the outcome (iodine gives starch a blue-black, tragacanth turns golden brown) alongside why it happens, then you can handle a straight "what colour" question and a "explain the result" question from the same fact. Always check the reactions against your own lab observations and your lecturer's outline, since a demonstrator may emphasise particular tests.
Will these exact questions appear in my exam?
No. This is an original revision set written from scratch to rehearse the reasoning and the phrasing, not a forecast of what your demonstrator will set. Use it to practise, then sit your practical on the specimens and outline your own course actually covers.
About this resource: All summaries, explanations, study tips, and practice questions on this page were written, paraphrased, and adapted by the EverythingABUAD student team to support exam revision. This is an original study aid, not an official ABUAD document, and it is not a prediction of any future exam.
