Subtopic: Fundamentals of Downstream processing (chromatography, filtration)
Question Statement:
Runs scored by a batsman in five one-day matches are 55, 75, 67, 88 and 15. The standard
deviation is __________________.
Options:
(A) Trypan blue dye exclusion
(B) Tetrazolium (MTT) assay
(C) LDH activity in the culture medium
(D) Coulter counter
Official Answer Key:
D
Step-by-Step Solution & Explanation
### **Official Solution & Step-by-Step Derivation (GATE BT 2016 Q.22)**
**1. Governing Concept & Question Classification**:
- **Section**: BT
- **Question Type**: **MCQ** (1 Mark)
- **Topic**: Animal Cell Culture & Bioanalytical Techniques (Cell Viability vs. Particle Counting)
**2. Detailed Step-by-Step Analysis**:
- A **cell viability assay** must discriminate between living (viable, metabolically active, intact membrane) cells and dead (non-viable) cells:
1. **Trypan blue dye exclusion**: Living cells with intact membranes exclude the dye, remaining clear; non-viable cells with damaged membranes take up trypan blue and stain dark blue. Measures membrane integrity viability.
2. **MTT assay**: Measures mitochondrial dehydrogenase activity in metabolically active, viable cells, which reduce yellow tetrazolium salt into purple insoluble formazan crystals.
3. **LDH (Lactate Dehydrogenase) assay**: Released into the culture medium only upon cell lysis and membrane rupture, quantitatively reporting on cytotoxicity and lost viability.
4. **Coulter counter**: An electronic particle counter that measures changes in electrical impedance as particles pass through an aperture. It counts total particle/cell numbers and measures particle size, but **cannot distinguish between viable and non-viable cells** of similar physical dimensions without specific auxiliary staining.
- **Option-by-Option Evaluation**:
- **Option (A) [INCORRECT]**: Trypan blue is a classic dye exclusion viability assay.
- **Option (B) [INCORRECT]**: MTT assay is a standard metabolic viability test.
- **Option (C) [INCORRECT]**: LDH release is a standard cell viability/cytotoxicity biomarker.
- **Option (D) [CORRECT]**: A Coulter counter measures particle numbers and volume via electrical resistance and does not inherently assess viability.
**3. Final Answer / Verification Summary**:
- **Official GATE Answer Key**: **D**
- **Scoring Criteria**: +1.0 Mark (Negative marking: -0.33 marks).
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