An honours student needs to count the number of cells they have in a tube. They take an aliquot of the cells and dilute them 1:50 before loading 10 uL into a haemocytometer to perform a cell count. They count 4 quadrants and obtain the following counts for each quadrant: 12, 5, 17, 9.

Which of the following statements is the most correct?

Question

An honours student needs to count the number of cells they have in a tube. They take an aliquot of the cells and dilute them 1:50 before loading 10 uL into a haemocytometer to perform a cell count. They count 4 quadrants and obtain the following counts for each quadrant: 12, 5, 17, 9.

Which of the following statements is the most correct?

BlackTom AI · Accepted Answer

The scenario involves counting cells in a haemocytometer after an aliquot has been diluted 1:50, and then loading 10 μL to count across four quadrants with counts of 12, 5, 17, and 9.
First, compute the average cell count per counted square: (12 + 5 + 17 + 9) / 4 = 43 / 4 = 10.75 cells per square.
Next, apply the standard haemocytometer calculation. The volume represented by one counted square in a standard haemocytometer is 1 x 10^-4 mL (since each large square has a depth of 0.1 mm). Therefore, cells per mL in the diluted sample = average cells per square × dilution factor × 10^4 = 10.75 × 50 × 10^4 = 10.75 × 500,000 = 5,375,000 cells/mL, which is 5.375 × 10^6 cells/mL when rounded.

Option A states a plan to perform a new 1:5 dilution and repeat counting. This would change the dilution factor and is not consistent with the given 1:50 dilution nor with the calculated concentration, making this suggestion incorrect.
Option B asserts the original flask's concentration is 5.4 × 10^6 cells/mL. Given the calculation above, this closely matches the computed value (5.375 × 10^6 cells/mL, rounded to 5.4 × 10^6), so this is a reasonable conclusion from the data.
Option C proposes a 1:100 dilution and repetition. Similar to A, this would alter the dilution factor and would not reflect the provided 1:50 dilution, making this option incorrect.
Option D gives 1.08 × 10^5 cells/mL, which is far smaller than the calculated 5.4 × 10^6. This discrepancy suggests a misapplication of the dilution factor or the volume-per-square calculation, indicating it is inaccurate.

In summary, the correct line of reasoning leads to a concentration on the order of several million cells per milliliter in the original flask, arising from the 1:50 dilution and the observed counts, with the 5.4 × 10^6 cells/mL figure aligning with the computed value after rounding. The other options either misstate the dilution step or miscalculate the conversion from counted cells to concentration, and thus are not consistent with the data and standard haemocytometer methodology.

MIMI2002 (ND) Immunology Practical Quiz

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