Using a haemocytometer an honours student performs a cell count on an undiluted sample of a single spleen cell suspension. Her 4 counts of the 4 indicated squares labelled A, B, C and D are shown below:

A = 36

B = 41

C = 39

D = 44

If the student transferred 1 mL of her cell suspension into a 15mL conical tube, how many cells would she have in the tube? (you may use a calculator and the piece of paper provided to help calculate your answer but you must select the most correct answer from the list of available options)

Question

Using a haemocytometer an honours student performs a cell count on an undiluted sample of a single spleen cell suspension. Her 4 counts of the 4 indicated squares labelled A, B, C and D are shown below:

A = 36

B = 41

C = 39

D = 44

If the student transferred 1 mL of her cell suspension into a 15mL conical tube, how many cells would she have in the tube? (you may use a calculator and the piece of paper provided to help calculate your answer but you must select the most correct answer from the list of available options)

BlackTom AI · Accepted Answer

First, I’ll restate the problem and the given data to ensure we’re working from the same numbers. The student has four counts from the haemocytometer squares: A = 36, B = 41, C = 39, D = 44. These four readings are averaged to estimate cell concentration in the undiluted sample. The student transferred 1 mL of the suspension into a 15 mL conical tube, so the total number of cells in that 1 mL aliquot will be the concentration (in cells per mL) times 1 mL.

Option-by-option analysis:
- 40 cells: This is far too small as a result for an undiluted haemocytometer readout. It does not reflect the typical scale of counts in a 1 mL sample when using a haemocytometer. The number in a single small square is on the order of a few dozen cells, and summing over multiple squares, the total in 1 mL would be much larger than 40.

- 4.4 x 105 cells: Here, 4.4 x 10^5 cells is being presented. This aligns well with the standard conversion from average count per square to cells per milliliter for an undiluted sample in a Neubauer chamber. The typical rule is: cells/mL = average cells per counting square × 10^4. The average in this case is (36 + 41 + 39 + 44) / 4 = 40. Multiplying by 10^4 yields 4.0 x 10^5 cells/mL, i.e., 4 x 10^5 cells in 1 mL. Therefore 4.4 x 10^5 is not the exact value expected, though it is in the same order of magnitude; it overestimates slightly relative to the standard calculation.

- 2.4 x 106 cells: This implies 2.4 million cells in 1 mL. That would require an average per square of 2.4 x 10^6 / 10^4 = 240 cells per square, which is far higher than the observed counts (36–44 per square). This is inconsistent with the actual data and method used, so it is incorrect.

- 6 x 106 cells: This is six million cells per mL. Again, this would require a much larger average count per square than observed, and it grossly contradicts the given counts. It is not plausible from the data, so it is incorrect.

- 3.6 x 105 cells: This is 3.6 x 10^5 cells in 1 mL. If we compute using the standard conversion with the exact average 40, we get 4.0 x 10^5 cells/mL, which is close to this value but not exact. Given the instruction to select the most correct answer from the provided options, this is a plausible distractor but not the precise calculated value from the data provided.

- 1.6 x 106 cells: This would require an average of 1.6 x 10^6 / 10^4 = 160 cells per square, which again does not match the observed counts (which average to 40 per square). Therefore, incorrect.

- 600 cells: This is far too low for a 1 mL volume and contradicts the typical scale of counts per mL from these data. It would imply an average per square of 0.06 cells, which is impossible in this setup.

- 4 x 105 cells: This exactly matches the standard calculation using the average count per square. With A = 36, B = 41, C = 39, D = 44, the total is 160; the average per square is 160/4 = 40. For an undiluted sample in a haemocytometer, cells per mL = average per square × 10^4 = 40 × 10^4 = 4.0 × 10^5 cells/mL. Therefore, 4 x 10^5 cells is the precise, correct result for the 1 mL transfer.

- 2400 cells: This would correspond to 2.4 x 10^3 cells in 1 mL, which is far too low given the counts. It does not reflect the standard calculation and is incorrect.

- 15 cells: This is far too small and would imply an average per square of roughly 0.15 cells, which is impossible with the observed counts. Incorrect.

- 160 cells: This would be the total of the four counts (36 + 41 + 39 + 44 = 160) but not scaled to the concentration per mL. Since the problem asks for the number of cells in the 1 mL transferred into the tube, this number does not account for the 10^4 factor used to convert to cells per mL. Therefore, this option is incorrect as the total in 1 mL is larger.

In summary, applying the standard haemocytometer conversion with an undiluted sample gives a precise result of 4 x 10^5 cells in the 1 mL aliquot. Among the provided options, 4 x 10^5 cells is the correct match to the calculation, while the other choices are either misapplied conversions or inconsistent with the observed counts.

IMMU2011 2025 Theory of practical exam 2025

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