Q.81 The concentration of sodium chloride in the cytoplasm of a Halobacterium sp. was found to be
250 ng/nl. The molarity (in M) of sodium chloride is __________.
Halobacterium Cytoplasm NaCl 250 ng/nl Molarity Calculation
halobacterium nacl cytoplasm molarity
Halobacterium sp., an extremophilic archaeon, thrives in hypersaline environments with high intracellular salt. Question 81 tests unit conversion skills in halobacterium nacl cytoplasm molarity, common in GATE Biotech and CSIR NET exams. The cytoplasm NaCl concentration is 250 ng/nl; find molarity in M (fill-in-the-blank).
✅ Correct Answer: 4278 M
Molarity (M) = moles of NaCl per liter of solution. Here’s the exact calculation:
- Step 1: Molar mass of NaCl = 58.44 g/mol.
- Step 2: Convert 250 ng/nl to g/L.
1 ng = 10⁻⁹ g; 1 nl = 10⁻⁹ L.
250 ng/nl = 250 × 10⁻⁹ g / 10⁻⁹ L = 250 g/L. - Step 3: M = (250 g/L) ÷ 58.44 g/mol ≈ 4277.89 M ≈ 4278 M (rounded for exams).
📐 Key Formula:
M = conc(g/L) / MW(g/mol)
250 g/L ÷ 58.44 g/mol = 4.278 M × 10³ = 4278 M
🔬 Why This Makes Sense for Halobacterium
Halobacterium requires 3-5 M NaCl externally and maintains high cytoplasmic levels (~4 M) for protein solubility and osmotic balance. 250 ng/nl (4278 mM) fits perfectly—far from dilute solutions (e.g., seawater ~0.5 M).
Errors often stem from unit mix-ups like ng/ml instead of ng/nl.
⚠️ Common Mistakes & Exam Traps
Since it’s numerical (no A/B/C/D options), watch these pitfalls in halobacterium nacl cytoplasm molarity problems:
| Mistake | Wrong Calculation | Result (M) | Why Wrong |
|---|---|---|---|
| Treat as ng/ml | 250 ng/ml = 0.25 mg/ml = 0.25 g/L | ~0.0043 | nl ≠ ml; underestimates by 10⁶ |
| Wrong MW | Use 58 g/mol | ~4310 | Precise MW is 58.44 |
| g/L error | 250 × 10⁻⁶ g/L | ~0.0043 | Ignores nl = 10⁻⁹ L scaling |
🎯 Exam Tips for Numerical Questions
- Always confirm units: ng/nl = g/L directly
- Practice Halobacterium biology: Salt-adapted proteins need KCl/NaCl >4 M
- Exams accept 4278 or 4.28 × 10³
- Double-check: 1 ng/nl = 1 g/L (perfect 1:1 conversion)
