A sample of blood was taken, and a 1 in 100 dilution made. The diluted sample was added to a haemocytometer and the cells counted in each of four of the central 1mm2 sections. The number of cells counted were 7, 4, 6 and 7. What is the average number of cells that was counted per μl?
Question
A sample of blood was taken, and a 1 in 100 dilution made. The diluted sample was added to a haemocytometer and the cells counted in each of four of the central 1mm2 sections. The number of cells counted were 7, 4, 6 and 7. What is the average number of cells that was counted per μl?
Solution
Sure, let's break it down step by step:
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Count the total number of cells in the four sections:
- Section 1: 7 cells
- Section 2: 4 cells
- Section 3: 6 cells
- Section 4: 7 cells
Total cells = 7 + 4 + 6 + 7 = 24 cells
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Calculate the average number of cells per section:
- Average cells per section = Total cells / Number of sections
- Average cells per section = 24 / 4 = 6 cells per section
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Determine the volume of each section in the haemocytometer:
- Each section is 1mm² in area and the depth of the haemocytometer is typically 0.1mm.
- Volume of each section = Area × Depth = 1mm² × 0.1mm = 0.1mm³
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Convert the volume from mm³ to μl:
- 1mm³ = 1μl
- Therefore, 0.1mm³ = 0.1μl
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Calculate the average number of cells per μl in the diluted sample:
- Average cells per μl = Average cells per section / Volume of section
- Average cells per μl = 6 cells / 0.1μl = 60 cells/μl
-
Account for the dilution factor:
- The original sample was diluted 1 in 100, meaning the diluted sample is 1/100th the concentration of the original.
- Therefore, the concentration in the original sample is 100 times the concentration in the diluted sample.
-
Calculate the average number of cells per μl in the original sample:
- Average cells per μl in original sample = Average cells per μl in diluted sample × Dilution factor
- Average cells per μl in original sample = 60 cells/μl × 100 = 6000 cells/μl
So, the average number of cells that was counted per μl in the original sample is 6000 cells/μl.
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