cell counts

Question 1

This lesson covers two methods of counting cells:

Manual cell counting using a haemocytometer.

Automated cell counting using a Coulter counter

Answer 1

.

Question 2

What Is a Haemocytometer?

🔍 Key Features:

Answer 2

A haemocytometer is a special microscope slide used to count cells in a known volume of fluid.

Contains gridded chambers with a known depth and defined area.

Enables the calculation of cell concentration in a known volume of liquid sample.

Works like a quadrat, allowing you to count the number of cells in a set area under the microscope.

Question 3

Structure of the Grid

Answer 3

The slide has two chambers, each with a known depth.

Large squares in the corners measure 1 mm² – suitable for counting larger cells (e.g. white blood cells).

The central square is divided into smaller squares – used for counting smaller cells like red blood cells.

Higher magnification is needed to view smaller grids.

Question 4

Rules for Using a Haemocytometer

Answer 4

📌 Sample Preparation
Dilute the sample if it’s too concentrated – overcrowded grids make counting difficult.

Ensure the dilution allows for clear visibility of individual cells within the grid.

📌 Selecting the Correct Grid
Use corner squares for larger cells.

Use the central grid for smaller cells.

📌 Consistent Counting Rules
To avoid double-counting or missing cells:

Count only cells fully inside the square.

Or, count cells touching the top and left edges, but ignore those on the bottom and right.

Question 5

Rules for Using a Haemocytometer

Answer 5

tips for Accurate Counting
Use a click counter to tally cells without losing track.

Use a stain to improve visibility:

Trypan Blue stains dead (non-respiring) cells blue.

Living cells remain colourless as they reduce the dye due to respiration occuring.

Question 6

Calculating Cell Concentration

Answer 6

Count cells in selected squares.

Repeat the count across multiple squares (e.g. four corners or five diagonals).

Calculate the mean number of cells.

Multiply by the dilution factor (if sample was diluted).

Use the formula:

Concentration (cells per mm³ or cm³) = (mean cell count × dilution factor) ÷ volume of chamber

Question 7

Alternative Method: Coulter Counter
A Coulter counter is an automated device used to count cells more efficiently.

⚙️ How It Works:

Answer 7

Two electrodes are placed on either side of a small aperture.

The cell suspension is drawn through the aperture.

Each cell causes a change in electrical resistance, recorded as a peak on a graph.

📈 Peak Analysis:
Number of peaks = number of cells.

Height of peaks = relative size of the cells.

Question 8

Advantages of a Coulter Counter

Answer 8

🔄 Automated – reduces human error.

⚡ Fast – processes large volumes quickly.

🔍 Sensitive – detects small cells not easily seen under a light microscope.

Question 9

Disadvantages

Answer 9

🚫 Cannot distinguish living from dead cells (no staining).

🧫 Cannot identify cell types without separate analysis.

⚠️ May miscount particles in mixed cultures unless pre-sorted.