- Given below are some statements on secondary metabolites in plants.
A. Glucosinolates are synthesized by elongation in the length of side chains of their precursor amino acids
B. All terpenes produced in herbs and spices are sticky. oily liquids which reduces the palarability (edible value) of these plants.
C. Cyanogenic glycosides are produced and stored in a toxic lour in plants and are therefore more
effective in defense against invading pathogens and herbivores.
D. The defense molecules,alkaloids (or their precursors), are gathered from plants and used by some insects for their own protection against predators.
Which one of the following represents correct statements?
(1) B and C only
(2) A and B only
(3) C only
(4) A and D only
Correct answer: (4) A and D only
Correct statements
A. Glucosinolates and side-chain elongation
Glucosinolates are synthesized from amino acids such as methionine, phenylalanine or tryptophan, and many aliphatic glucosinolates arise through elongation of the amino-acid side chain (R-group) before formation of the glucosinolate core.
This elongation step adds methylene units to the side chain and is a defining feature of aliphatic glucosinolate biosynthesis, so statement A is correct.
D. Insects using plant alkaloids for defense
Many insects sequester plant defense molecules like alkaloids (for example, pyrrolizidine alkaloids) and store them for their own protection against predators, sometimes also using them as pheromone precursors.
This co‑option of plant toxins for insect defense is well documented, so statement D is correct.
Incorrect statements
B. Terpenes in herbs and spices
Terpenes in herbs and spices are often volatile, aromatic compounds that contribute desirable flavors and aromas, and many are not sticky, nor do they universally reduce palatability; in fact they frequently increase culinary value.
Therefore the claim that all such terpenes are sticky, oily liquids that reduce edibility is incorrect.
C. Cyanogenic glycosides storage form
Cyanogenic glycosides are typically stored in plants as non‑toxic or protoxic glycosides, spatially separated from activating β‑glucosidases; toxicity (HCN release) occurs only after tissue damage.
So the statement that they are “produced and stored in a toxic form” is wrong; their effectiveness arises from activated release upon attack, not constitutive toxicity.
