Alkaloids: Nicotine, Morphine, Codeine, Strychnine and Caffeine
Biology · Biomolecules · NEET
Alkaloids are secondary metabolites made by plants. The five NCERT examples are nicotine, morphine, codeine, strychnine and caffeine. Memory hook: "Nice Morning, Cousin Steve Called" = Nicotine, Morphine, Codeine, Strychnine, Caffeine. NEET tests them by asking you to match each name to the class "alkaloid" in Table 9.3.
The secondary metabolite table: alkaloids (nicotine, morphine, codeine, strychnine, caffeine) sit alongside separate classes for toxins, drugs, lectins and terpenoids. NEET matches each example to its correct class.
Your doubts, answered
Are alkaloids primary or secondary metabolites?
Alkaloids are SECONDARY metabolites. In NCERT, primary metabolites are amino acids, sugars (glucose), nucleotides etc. that have a clear role in normal body processes. Alkaloids like morphine and codeine have no obvious role in the plant's own basic life processes, so they are placed in the secondary metabolite table (Table 9.3). This exact primary-vs-secondary trap was asked in NEET 2021.
Is caffeine an alkaloid?
Yes. Caffeine is an alkaloid, and alkaloids are one class of secondary metabolites. Students confuse caffeine because they think of it as a food or drink chemical, but in NCERT it sits with nicotine and strychnine as an alkaloid. Remember: caffeine, nicotine, strychnine are grouped together as defence alkaloids.
Why do plants make alkaloids like nicotine and strychnine?
Mainly for DEFENCE. Alkaloids taste bitter or are toxic, so they stop insects and animals from eating the plant. NEET 2020 asked exactly this: nicotine, strychnine and caffeine are produced for 'defence action', not for nutrition, reproduction or growth.
What is the difference between an alkaloid and a toxin in NCERT?
Both are secondary metabolites, but they are DIFFERENT classes in Table 9.3. Alkaloids = morphine, codeine, nicotine, strychnine, caffeine. Toxins = abrin, ricin. A common NEET trap pairs 'Alkaloid - Codeine' (correct) against 'Toxin - Ricin' (correct) and 'Drug - Ricin' (WRONG). Ricin is a toxin, not a drug.
Is morphine a drug or an alkaloid in the NCERT table?
In Table 9.3 morphine and codeine are listed under ALKALOIDS. The 'Drugs' class in the same table is vinblastin and curcumin. So if an option says 'Drug - Morphine' it is wrong; the correct pair is 'Alkaloid - Morphine'.
⚠️ The NEET trap ✗ Pairing 'Drugs - Ricin' as a correct match, or thinking morphine/codeine are 'drugs' in the NCERT table. ✓ Ricin is a TOXIN (with abrin). Morphine and codeine are ALKALOIDS. The 'Drugs' class in Table 9.3 is only vinblastin and curcumin. 🧠 NEET loves the odd-one-out match. Fix each class to its example: Alkaloid=codeine/morphine, Toxin=ricin/abrin, Drug=vinblastin/curcumin, Lectin=concanavalin A.
Real NEET questions
NEET 2020
Secondary metabolites such as nicotine, strychnine and caffeine are produced by plants for their:
A · Defence action ✓
B · Effect on reproduction
C · Nutritive value
D · Growth response
Solution: Nicotine, strychnine and caffeine are alkaloids, a class of secondary metabolites. Plants make them chiefly to defend against herbivores and pathogens (they are bitter or toxic), so the correct role is defence action, not nutrition, reproduction or growth.
NEET 2021
Which of the following are not secondary metabolites in plants?
A · Vinblastin, curcumin
B · Rubber, gums
C · Morphine, codeine
D · Amino acids, glucose ✓
Solution: Amino acids and glucose are PRIMARY metabolites with clear roles in normal metabolism. Morphine and codeine (alkaloids), rubber, gums, and drugs like vinblastin/curcumin are all secondary metabolites. So amino acids and glucose are the odd pair out.
NEET 2021
Identify the incorrect pair.
A · Lectins - Concanavalin A
B · Drugs - Ricin ✓
C · Alkaloids - Codeine
D · Toxin - Abrin
Solution: In Table 9.3, ricin is a TOXIN, not a drug (drugs are vinblastin and curcumin). Concanavalin A is a lectin, codeine is an alkaloid, and abrin is a toxin, so those three pairs are correct. 'Drugs - Ricin' is the incorrect pair.
Solved Biomolecules NEET PYQs
Try the real previous-year questions from this chapter — each with the answer and a full solution.
How many alkaloid examples should I remember for NEET?
Learn the five NCERT names: nicotine, morphine, codeine, strychnine and caffeine. Table 9.3 also names 'etc.', but these five are the ones NEET repeats in match and odd-one-out questions.
Which chapter and table has alkaloids?
Class 11 Biology, Chapter 'Biomolecules' (Ch 9), Table 9.3 on secondary metabolites. Alkaloids are one row, with morphine and codeine given as examples.
Are alkaloids nitrogen-containing?
Yes, alkaloids are nitrogen-containing basic organic compounds. NEET does not test their formula, but knowing they contain nitrogen helps you separate them from terpenoids and pigments.
Do alkaloids appear every year in NEET?
The secondary metabolite table is a high-frequency NEET topic. Alkaloids, lectins and toxins have been matched in 2019, 2020, 2021, 2023 and 2026 papers, so memorising each class-to-example pair is worth easy marks.
