Correct option is A
Correct Answer: (a)
Explanation: Plants absorb sulfur predominantly in the form of sulfate (SO₄²⁻). Sulfate is first reduced to sulfite (SO₃²⁻) and then further reduced to sulfide (S²⁻) in a series of enzymatic steps. The reduced sulfide is finally incorporated into the amino acid cysteine (Cys), which serves as the primary organic form of sulfur in plants. This sequence represents the correct biochemical conversion pathway.
Information Booster
· Sulfate reduction occurs mainly in plastids of plant cells.
· ATP sulfurylase initiates sulfate activation before reduction.
· Sulfite reductase catalyzes the conversion of sulfite to sulfide.
· Cysteine is the first stable organic sulfur-containing compound formed.
· Cysteine acts as a sulfur donor for other biomolecules like methionine and glutathione.
Additional Knowledge
Options involving glutamine (Gln) are incorrect because glutamine is a nitrogen-containing amino acid and does not incorporate sulfur. Pathways starting with sulfide as the absorbed form are also incorrect since plants take up sulfur mainly as sulfate from the soil. The stepwise reduction from sulfate to sulfide followed by incorporation into cysteine is a tightly regulated and essential process in plant sulfur metabolism.
