10. Secondary metabolites are diverse array organic compounds in plants. The following are certain statements about secondary metabolites:
A. They protect plants against being eaten by herbivores and against being infected by pathogens.
B. Terpenes, the largest class of secondary metabolite, are synthesized by methyl erythritol phosphate(MEP) pathway and shikimic acid pathway.
C. The mast abundant classes of phenolic compounds in plants are derived from phenylalanine.
D. Alkaloids are nitrogen containing secondary metabolites in plants.
Which one of the following
combinations of the above
statements is correct?
(1) A, B and C
(2) B, C and D
(3) A, C and D
(4) A, B and D

Correct answer: (3) A, C and D

Explanation:

• (A) is true: Secondary metabolites play important roles in protecting plants against herbivores and pathogens through defense chemicals.

• (B) is false: Terpenes, the largest class of secondary metabolites, are synthesized via the MEP pathway and the Mevalonic acid pathway, NOT the shikimic acid pathway. The shikimic acid pathway produces aromatic compounds, not terpenes.

• (C) is true: The most abundant phenolic compounds in plants are derived from phenylalanine, an amino acid produced via the shikimic acid pathway.

• (D) is true: Alkaloids are nitrogen-containing secondary metabolites that commonly have pharmacological activity.

Option-wise:

• (1) A, B and C — B is false.

• (2) B, C and D — B is false.

• (3) A, C and D — correct.

• (4) A, B and D — B is false.

Plant secondary metabolites have diverse functions including defense against herbivores and pathogens. Terpenes are synthesized through MEP and mevalonic acid pathways, phenolics originate from phenylalanine via the shikimic acid pathway, and alkaloids contain nitrogen, underscoring the chemical diversity linked to plant survival.