Tok Essay
Title: Counting the Number of Yeast Cells in a Suspension using Haemocytometer
Objective: To estimate the number of cells of yeast per mm3 in five different dilutions of yeast suspension.
Introduction: Biologists often need to count the density of cells in a liquid. “Density of cells” means “the number of cells per unit volume of liquid”. For example, they might want to find out the density of red blood cells in blood plasma, the density of bacteria in milk, or the population of Paramecium sp. (a protozoan) in water from a pond.
The simplest, most convenient and cheapest means of accurately determining the number of cells in a sample is to use a haemocytometer and a microscope. A haemocytometer is a specialised slide that has a counting chamber with a known volume of liquid. The haemocytometer is a device originally designed for the counting of blood cells. It is now also used to count other types of cells as well as other microscopic particles.
The haemocytometer was invented by Louis-Charles Malassez and consists of a thick glass microscope slide with a rectangular indentation that creates a chamber. This chamber is engraved with a laser-etched grid of perpendicular lines. The device is carefully crafted so that the area bounded by the lines is known, and the depth of the chamber is also known. It is therefore possible to count the number of cells or particles in a specific volume of fluid, and thereby calculate the concentration of cells in the fluid overall.
The haemocytometer consists of a heavy glass slide with two counting chambers, which is 0.1mm deep, each of which is divided into nine large 1mm squares, on an etched and silvered surface separated by a trough. A cover slip sits on top of the raised supports of the ‘H’ shaped troughs enclosing both chambers. There is a ‘V’ notch at either end where the cell suspension is loaded into the haemocytometer. When loaded with the cell suspension it contains a defined volume of liquid. The engraved grid on
Objective: To estimate the number of cells of yeast per mm3 in five different dilutions of yeast suspension.
Introduction: Biologists often need to count the density of cells in a liquid. “Density of cells” means “the number of cells per unit volume of liquid”. For example, they might want to find out the density of red blood cells in blood plasma, the density of bacteria in milk, or the population of Paramecium sp. (a protozoan) in water from a pond.
The simplest, most convenient and cheapest means of accurately determining the number of cells in a sample is to use a haemocytometer and a microscope. A haemocytometer is a specialised slide that has a counting chamber with a known volume of liquid. The haemocytometer is a device originally designed for the counting of blood cells. It is now also used to count other types of cells as well as other microscopic particles.
The haemocytometer was invented by Louis-Charles Malassez and consists of a thick glass microscope slide with a rectangular indentation that creates a chamber. This chamber is engraved with a laser-etched grid of perpendicular lines. The device is carefully crafted so that the area bounded by the lines is known, and the depth of the chamber is also known. It is therefore possible to count the number of cells or particles in a specific volume of fluid, and thereby calculate the concentration of cells in the fluid overall.
The haemocytometer consists of a heavy glass slide with two counting chambers, which is 0.1mm deep, each of which is divided into nine large 1mm squares, on an etched and silvered surface separated by a trough. A cover slip sits on top of the raised supports of the ‘H’ shaped troughs enclosing both chambers. There is a ‘V’ notch at either end where the cell suspension is loaded into the haemocytometer. When loaded with the cell suspension it contains a defined volume of liquid. The engraved grid on