Alkaloids — Occurrence & Physiological Effects (Detailed notes)

Alkaloids

Alkaloids are nitrogen-containing, basic (alkaline) organic compounds produced mainly by plants. They often have strong physiological and medicinal effects on humans and animals.

1. Occurrence of Alkaloids

Alkaloids are widely distributed in the plant kingdom, but their concentration and type vary among species.
Below are exam-friendly headings with examples:

A. Occurrence in Plant Kingdom

1. Angiosperms (Flowering Plants) — Major Source

Most alkaloids come from higher plants, especially dicots.
Families rich in alkaloids:

Solanaceae – e.g., Atropa belladonna (atropine), Datura stramonium (scopolamine)
Papaveraceae – e.g., Papaver somniferum (morphine, codeine)
Rubiaceae – e.g., Coffea arabica (caffeine)
Apocynaceae – e.g., Catharanthus roseus (vincristine, vinblastine)
Rutaceae – e.g., citrus plants (quinoline alkaloids)
Fabaceae – e.g., Cicer, Lupinus (quinolizidine alkaloids)

These families are 100% important for exams.

2. Gymnosperms

Only a few gymnosperms produce alkaloids.
Example: Ephedrine from Ephedra (a gymnosperm).

3. Lower Plants

Fungi – Ergot alkaloids (e.g., ergotamine from Claviceps purpurea)
Some marine organisms – produce indole and pyridine alkaloids

4. Specific Plant Parts Where Alkaloids Accumulate

Alkaloids can be present in almost any part:

Roots – ipecac alkaloids
Bark – quinine (Cinchona bark)
Leaves – nicotine (tobacco leaves)
Seeds – strychnine (Nux-vomica seeds)
Latex – morphine (opium poppy latex)

This classification helps students memorize occurrence systematically.

2. Physiological Effects of Alkaloids

Alkaloids are powerful bioactive chemicals. Their effects are mostly on the nervous system, but many act on the heart, muscles, smooth muscles, and metabolism.

Below are major categories, each with examples.

A. Effects on Central Nervous System (CNS)

1. CNS Depressants (Sedatives/Analgesics)

Morphine

Strong pain reliever
Causes sedation and euphoria
Medical use: analgesic in surgery

Codeine

Mild analgesic
Cough suppressant

2. CNS Stimulants

Caffeine

Stimulates brain & heart
Reduces fatigue
Increases alertness

Cocaine
Powerful CNS stimulant
Causes euphoria; highly addictive
Medical use: local anaesthetic in eye/nose surgery

B. Effects on Autonomic Nervous System

1. Parasympathetic Blockers

Atropine (Atropa belladonna)
Dilates pupils
Relaxes smooth muscles
Increases heart rate
Used in eye examinations and poison treatments

2. Sympathetic Stimulants

Ephedrine (Ephedra)
Increases heart rate
Raises blood pressure
Used in asthma and nasal decongestion

C. Effects on Muscles

1. Neuromuscular Blockers

Tubocurarine (from Chondrodendron tomentosum)
Causes muscle relaxation
Used during surgery to relax skeletal muscles

D. Effects on the Heart

Quinidine (from Cinchona)
1. Controls abnormal heart rhythms (antiarrhythmic)
Veratrine (from Veratrum)
1. Slows heart rate (toxic)

E. Anticancer Effects

Vincristine & Vinblastine (from Catharanthus roseus)
Inhibit cell division
Used to treat leukemia, Hodgkin’s lymphoma
Mechanism: block spindle formation during mitosis

F. Effects on Smooth Muscles & GIT

Papaverine
Relaxes smooth muscles
Used to treat spasms & blood vessel dilation

G. Toxic / Poisonous Alkaloids

These have a long history in anthropology & medicine.

Strychnine (Nux-vomica)
Causes convulsions
Extremely toxic
Coniine (Poison hemlock)
Causes paralysis
Famous for the death of Socrates

3. Summary (Exam-Ready Lines)

Alkaloids are naturally occurring nitrogen-containing basic compounds.
Occur mainly in dicot plants, especially Solanaceae, Papaveraceae, Rubiaceae, Apocynaceae, and Fabaceae.
Present in roots, leaves, seeds, bark and latex of plants.
They have strong physiological effects, mostly on the nervous system, heart, muscles, and smooth muscles.
Important alkaloids include morphine, codeine, atropine, quinine, caffeine, nicotine, vincristine, and strychnine.
They may be medicinal or toxic depending on the dose.

✅ MCQs on Alkaloids (With Answers)

1. Most alkaloids in plants are synthesized from:

A. Lipids
B. Amino acids
C. Steroids
D. Fatty acids
Answer: B

2. Morphine is obtained from:

A. Cinchona bark
B. Tobacco leaves
C. Opium poppy latex
D. Hemlock seeds
Answer: C

3. Which plant contains atropine?

A. Atropa belladonna
B. Papaver somniferum
C. Coffea arabica
D. Ephedra
Answer: A

4. Caffeine belongs to which class of alkaloids?

A. Tropane
B. Isoquinoline
C. Purine
D. Piperidine
Answer: C

5. Ephedrine is obtained from:

A. Datura
B. Ephedra
C. Cinchona
D. Veratrum
Answer: B

6. Strychnine is used as:

A. Heart stimulant
B. Sedative
C. Poison
D. Muscle relaxant
Answer: C

7. Quinine is primarily used for treatment of:

A. Asthma
B. Malaria
C. Hypertension
D. Diabetes
Answer: B

8. Which alkaloid is used in eye examinations to dilate pupils?

A. Morphine
B. Atropine
C. Cocaine
D. Nicotine
Answer: B

9. Vincristine is used in treatment of:

A. Typhoid
B. Heart failure
C. Cancer
D. Tuberculosis
Answer: C

10. Coniine is obtained from:

A. Poison hemlock
B. Neem tree
C. Opium poppy
D. Belladonna
Answer: A

✅ Additional 10 MCQs on Alkaloids (With Answers)

11. Which of the following is an indole alkaloid?

A. Morphine
B. Vincristine
C. Atropine
D. Nicotine
Answer: B

12. The main function of alkaloids in plants is believed to be:

A. Storage of food
B. Attraction of pollinators
C. Defense against herbivores
D. Water retention
Answer: C

13. Nicotine acts primarily on which system?

A. Digestive system
B. Skeletal system
C. Nervous system
D. Endocrine system
Answer: C

14. Ergotamine is produced by:

A. Papaver somniferum
B. Claviceps purpurea
C. Atropa belladonna
D. Cinchona officinalis
Answer: B

15. Which alkaloid is used as a muscle relaxant in surgeries?

A. Morphine
B. Tubocurarine
C. Quinine
D. Codeine
Answer: B

16. The alkaloids vinblastine and vincristine interfere with:

A. Protein synthesis
B. Lipid metabolism
C. Spindle fiber formation during mitosis
D. DNA replication
Answer: C

17. Which of the following contains a pyridine ring?

A. Nicotine
B. Morphine
C. Atropine
D. Quinine
Answer: A

18. Alkaloids are generally:

A. Acidic in nature
B. Basic (alkaline) in nature
C. Neutral compounds
D. Metallic salts
Answer: B

19. Quinine is obtained from which part of the Cinchona tree?

A. Leaves
B. Fruit
C. Bark
D. Seeds
Answer: C

20. Cocaine is medically used as:

A. General anesthetic
B. Local anesthetic
C. Antipyretic
D. Antibiotic
Answer: B

10 additional MCQs (with answers) — “more 10 MCQs boss”

Which family commonly contains tropane alkaloids like atropine?
A. Fabaceae B. Solanaceae C. Poaceae D. Asteraceae
Answer: B (Solanaceae).
Which alkaloid is primarily responsible for the addictive properties of tobacco?
A. Morphine B. Nicotine C. Quinine D. Atropine
Answer: B (Nicotine).
Which reagent produces a cream-colored precipitate with many alkaloids?
A. Benedict’s reagent B. Mayer’s reagent C. Sudan III D. Biuret reagent
Answer: B (Mayer’s reagent).
Which alkaloid is the principal active antimalarial used historically?
A. Caffeine B. Morphine C. Quinine D. Atropine
Answer: C (Quinine).
Which effect is typical of atropine overdose?
A. Increased salivation B. Miosis (constricted pupils) C. Dry mouth and tachycardia D. Hypoglycemia
Answer: C (Dry mouth and tachycardia).
Caffeine primarily acts by blocking which endogenous signalling molecule?
A. Dopamine B. Adenosine C. GABA D. Acetylcholine
Answer: B (Adenosine).
Which alkaloid is a potent analgesic extracted from opium latex?
A. Quinine B. Nicotine C. Morphine D. Cocaine
Answer: C (Morphine).
An ecological role of many plant alkaloids is to:
A. Stimulate photosynthesis B. Serve as main structural polymers C. Deter herbivores and pests D. Provide floral scent exclusively
Answer: C (Deter herbivores and pests).
Which alkaloid is used clinically as an antitussive (cough suppressant) in lower doses?
A. Quinine B. Codeine C. Nicotine D. Atropine
Answer: B (Codeine).
Overdose of opioid alkaloids like morphine most dangerously causes:
A. Hypertension B. Respiratory depression C. Increased appetite D. Hair loss
Answer: B (Respiratory depression).

Alkaloids: Occurrence & Physiological Effects — Interactive Quiz

Alkaloids — Occurrence & Physiological Effects (Quick Quiz)

Short interactive quiz to test knowledge on distribution, common alkaloids and their effects.

Topic: Alkaloids

Level: Intermediate

Instructions

Select the best answer for each multiple-choice question. Click "Next" to proceed. When you finish, press "Finish" to see your score and review answers.

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Alkaloids: Occurrence, Types, and Physiological Effects | Complete 2025 Biology Guide