18. The chemical salicyl hyrooxamic add (SHAM) inhibits
(1) Cytochrome oxidase
(2) Alternate oxidase
(3) ATP synthase
(4) NADH-dehydrogenase

Salicylhydroxamic acid (SHAM) inhibits the alternate oxidase (AOX) in the mitochondrial electron transport chain of plants.

Explanation of options:

• (1) Cytochrome oxidase is inhibited by cyanide, not SHAM.

• (2) Alternate oxidase is the specific target of SHAM; it inhibits this alternative pathway involved in cyanide-resistant respiration in plants.

• (3) ATP synthase is not inhibited by SHAM.

• (4) NADH-dehydrogenase is not inhibited by SHAM.

SHAM acts as a selective inhibitor of the alternative oxidase, blocking this bypass pathway that allows electrons to flow directly to oxygen without proton pumping, reducing ATP production and generating heat instead.​