Cell Count and Cell Viability Introduction to Cell Counting • Cell counting is essential for experiments in microbiology, cell biology, and biotechnology. • Accurate cell counts ensure consistent results across experiments and reliable scaling of cell cultures. • Typically performed using a hemocytometer or automated cell counter. Formula for Cell Count Using a Hemocytometer Total Cell Count = Average Cells per Square × Dilution Factor × 104 • Average Cells per Square: Mean number of cells counted across squares. • Dilution Factor: Accounts for any dilutions made to the sample. • 104 : Conversion factor based on the volume of one square on the hemocytometer. Example Problem: Cell Counting • You count 80, 70, 85, and 75 cells in four large squares of a hemocytometer. • The sample was diluted by a factor of 2. • Calculate the total cell count per mL. Solution • Step 1: Calculate the Average Cells per Square 80 + 70 + 85 + 75 4 = 77.5 Average = • Step 2: Use the Formula for Total Cell Count Total Cell Count = 77.5 × 2 × 104 = 1.55 × 106 cells/mL Answer: 1.55 × 106 cells/mL. Cell Viability • Cell viability measures the percentage of living cells in a population. • Vital stains like Trypan Blue are commonly used to differentiate live cells from dead cells. Formula for Cell Viability Viability(%) = Number of Live Cells × 100 Total Number of Cells Example Problem: Cell Viability 1 • You observe 150 live cells and 50 dead cells in a sample. • Calculate the cell viability. Solution • Step 1: Calculate Total Number of Cells Total Cells = 150 + 50 = 200 • Step 2: Use the Formula for Viability 150 × 100 200 = 75% Viability(%) = Answer: Cell viability is 75%. Practice Problems 1. You count 95, 90, 100, and 105 cells in four large squares of a hemocytometer. The sample was diluted by a factor of 5. Calculate the total cell count per mL. 2. In a sample stained with Trypan Blue, you observe 120 live cells and 30 dead cells. Calculate the cell viability. 2