Q.21 A callus of 5 g dry weight was inoculated on semi-solid medium for growth. The dry weight of the
callus was found to increase by 1.5 fold after 10 days of inoculation. The growth index of the
culture is _________
Callus Growth Index
5g Dry Weight → 1.5th Fold in 10 Days
📊 Given Data
Initial weight (W0): 5 g
Final weight: 5 × 1.5 = 7.5 g
Weight increase: 7.5 – 5 = 2.5 g
Time (t): 10 days
Final weight: 5 × 1.5 = 7.5 g
Weight increase: 7.5 – 5 = 2.5 g
Time (t): 10 days
🎯 Growth Index Formula
Final weight – Initial weight
7.5g – 5g = 2.5g
7.5g – 5g = 2.5g
÷
Initial weight × Time
5g × 10 days = 50
5g × 10 days = 50
🔢 Step-by-Step Division
2.5/50
GI = 0.05
Verification: 0.05 × 50 = 2.5g ✓ Perfect match!
❌ All Options Explained
| Option | Answer | Status | Why Correct/Wrong? |
|---|---|---|---|
| A | 0.05 | ✅ CORRECT | Proper formula: 2.5/50 = 0.05 |
| B | 0.15 | ❌ Wrong | Used 7.5/50 (final weight, not increase) |
| C | 1.5 | ❌ Wrong | Fold increase only (no time division) |
| D | 0.5 | ❌ Wrong | 2.5/5 only (forgot ×10 days) |
💡 Exam Memory Trick
Growth Index = (Increase ÷ Inoculum) ÷ Days
Or: ΔWeight / (W₀ × t)
