Question

Identify the chemicals produced by Calotropis that provide defense against grazers and browsers.

• A. Strychnine
• B. Quinine
• C. Cardiac glycosides
• D. Caffeine

Hint:

Key secondary metabolites and their sources:
$\bullet$ Calotropis $\rightarrow$ Cardiac glycosides (toxic to heart).
$\bullet$ Cinchona $\rightarrow$ Quinine (antimalarial).
$\bullet$ Strychnos $\rightarrow$ Strychnine (neurotoxin).
$\bullet$ Coffea $\rightarrow$ Caffeine (stimulant/insect deterrent).

Answer 1

The Correct Option is C

Concept:
In terrestrial ecosystems, plants have evolved diverse chemical and morphological adaptations to protect themselves from herbivores, grazers, and browsers.
Secondary metabolites such as alkaloids, glycosides, tannins, and resins act as deterrents, toxins, or digestion inhibitors.

Step 1: Analysis of Chemical Defense in Calotropis:
Calotropis is a resilient weed commonly found growing wild in abandoned agricultural fields and arid wastelands.
The plant produces a thick, milky latex throughout its vegetative tissues containing poisonous cardiac glycosides.
Cardiac glycosides disrupt the cardiac function of animals by inhibiting the cellular sodium-potassium ATPase pump ($Na^+/K^+$-ATPase).
This leads to severe neuromuscular and cardiovascular distress in grazing mammals.
Consequently, cattle, goats, and wild browsers avoid eating or browsing this plant.

Step 2: Examination of the Other Chemicals:
- Strychnine: A highly poisonous alkaloid extracted from the seeds of Strychnos nux-vomica.
- Quinine: An alkaloid extracted from the dried bark of Cinchona trees, famously used as an antimalarial drug.
- Caffeine: A purine alkaloid produced by plants like Coffea arabica and Camellia sinensis to inhibit insect herbivory.

Step 3: Conclusion and Final Selection:
Among the given choices, the specific chemical produced by Calotropis for defense against herbivores is cardiac glycosides.