Explanation
- A
Pulses
(a) Pulses. Rhizobium in root nodules of legumes (pulses) fixes atmospheric nitrogen. That association is the official key.
- B
Rice
(b) Rice. Rice paddies may host Azolla–Anabaena, not the classic Rhizobium root-nodule partnership of pulses.
- C
House bug
(c) House bug. Not a plant; an OCR-stray option. No nitrogen-fixing root association.
- D
Sugarcane
(d) Sugarcane. Not the textbook Rhizobium host; acetobacter associations are a different, later story and not this key.
Summary. Official key is (a) Pulses. Nitrogen-fixing bacteria (Rhizobium) nodulate legume roots. Rice, sugarcane and the insect option are not that pair. Honour the stored letter (a).
Same topic · past papers
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