Q.77. Match the process involved in nitrogen or sulfur cycle in Group I with the corresponding microbe
in Group II.
Group I
P. Denitrification
Q. Nitrogen fixation by free-living microbe
R. Oxidation of H2 S to sulfur
S. Nitrogen fixation by a symbiotic microbe
(A) P− 2, Q − 3, R− 4, S − 1
(B) P-2, Q-1, R-3, S-4
(C) P − 3, Q − 4, R− 1, S − 2
(D) P − 3, Q −1, R− 2, S −4
Group II
1. Azotobacter
2. Beggiatoa
3. Pseudomonas
4. Rhizobium
Nitrogen and sulfur cycles rely on specific microbes for key transformations like fixation and oxidation. Question 77 tests matching these processes to bacteria such as Pseudomonas and Rhizobium. The correct answer is option (B) P-2, Q-1, R-3, S-4.
Process-Microbe Matches
Denitrification (P) converts nitrates to nitrogen gas, performed by Pseudomonas (2).
Free-living nitrogen fixation (Q) occurs via Azotobacter (1), which fixes atmospheric N2 aerobically in soil.
H2S oxidation to sulfur (R) happens through Beggiatoa (3), a colorless sulfur bacterium in sediments.
Symbiotic nitrogen fixation (S) involves Rhizobium (4) in legume root nodules.
Options Breakdown
| Option | P (Denitrification) | Q (Free-living N-fix) | R (H2S to S) | S (Symbiotic N-fix) | Correct? |
|---|---|---|---|---|---|
| (A) | 2 (Pseudomonas) ✓ | 3 (Beggiatoa) ✗ | 4 (Rhizobium) ✗ | 1 (Azotobacter) ✗ | No |
| (B) | 2 (Pseudomonas) ✓ | 1 (Azotobacter) ✓ | 3 (Beggiatoa) ✓ | 4 (Rhizobium) ✓ | Yes |
| (C) | 3 (Beggiatoa) ✗ | 4 (Rhizobium) ✗ | 1 (Azotobacter) ✗ | 2 (Pseudomonas) ✗ | No |
| (D) | 3 (Beggiatoa) ✗ | 1 (Azotobacter) ✓ | 2 (Pseudomonas) ✗ | 4 (Rhizobium) ✓ | No |
Cycle Significance
These microbes maintain ecosystem balance by recycling nutrients. Pseudomonas prevents nitrate buildup via denitrification. Azotobacter and Rhizobium enrich soil nitrogen for plants. Beggiatoa controls sulfide toxicity in aquatic environments. Understanding these aids agriculture and exam prep like NEET.
