Q.17 The pH of cytoplasm and lysosomes are ~ 7 and ~5 respectively. How many fold H+ ion concentration is higher in lysosomes compared to cytoplasm?
1. 2
2. 50
3. 20
4. 100
Lysosome H+ Concentration vs Cytoplasm: 100-Fold Difference Explained
The pH difference between cytoplasm (~7) and lysosomes (~5) results in a 100-fold higher H⁺ ion concentration in lysosomes, making option 4 the correct answer.
pH and H⁺ Concentration Basics
pH measures acidity as pH=−log10[H+], where [H⁺] is in moles per liter (M).
Cytoplasm pH ~7 gives [H+]cytoplasm=10−7 M.
Lysosome pH ~5 gives [H+]lysosome=10−5 M, confirming higher acidity inside lysosomes.
Correct Answer Calculation
Fold difference = [H+]lysosome[H+]cytoplasm=10−510−7=102=100.
This matches the ~2 pH unit drop (each unit = 10-fold change).
V-ATPase proton pumps maintain this gradient for lysosomal enzyme function.
Option Explanations
| Option | Fold Value | Why Incorrect/Correct | Explanation |
|---|---|---|---|
| 1. 2 | 2-fold | Incorrect | Matches ~0.3 pH difference (100.3≈2), not 2 units. |
| 2. 50 | 50-fold | Incorrect | Matches ~1.7 pH units (101.7≈50), underestimates gap. |
| 3. 20 | 20-fold | Incorrect | Matches ~1.3 pH units (101.3≈20), too low for pH 5-7. |
| 4. 100 | 100-fold | Correct | Exact for 2 pH units (102=100). |
Biological Relevance
Lysosomes’ acidic pH activates hydrolases for waste breakdown; neutral cytoplasm protects other processes.
This gradient, ~100-fold H⁺ higher, prevents cytosolic damage while enabling digestion.
