2.1. OCULAR MICROMETER
Introduction
Ocular micrometer is a glass disk that fits in a microscope eyepiece that has a ruled scale, which is used to measure the size of magnified objects. The physical length of the marks on the scale depends on the degree of magnification. The scale allows the user to measure and compare the size of microbes observed. The lens need to be calibrated or adjusted. It is also need to be calibrated by using the stage micrometer. After calibration is done, the stage is changed with slide containing microorganisms. Hence, the dimension of the cells is identified.
Materials
- Microscope fitted with an ocular micrometer
- Slide micrometer
- Stained preparation of yeast and bacteria
Objectives
- To master the usage of micrometer
- To measure the dimension of the microbes
- To identified size of different microbes
Methodology
- The stage micrometer was placed on the stage.
- The superimposed on the eyepiece scale on the micrometer stage is focused using the lowest power objective.
- The divisions of the eyepiece scale correspond top a definite number of divisions on the stage scale are determined.
- The measurement of an eyepiece division in micrometer (μm) is calculated.
- The steps are repeated using high-power objectives lens and oil-immersion objective.
Observation
For the first step calibration
were performed to find it true value of measurement for the ocular micrometer
then 10 random cell was selected for measurement of the size of a cell. The cell
were measured then average size cell were calculated using formula from
below:
(
average size cell= total size of all cell/number of cell)
The average size cell was calculated by using the measurement below :
1 eyepiece divission = 1μm line on eyepiece
40X magnification = 25μm
100X magnification = 10μm
400X magnification = 2.5μm
1000X magnification = 1μm
Result
Pick random 10 cell than measure it size
using ocular micrometer
Cell
|
Diameter
(μm)
|
1
|
10
|
2
|
10
|
3
|
5
|
4
|
6
|
5
|
5
|
6
|
8
|
7
|
6
|
8
|
4
|
9
|
5
|
10
|
5
|
Average cell diameter = total diameter of cells / total number of cells
= (10+10+5+6+5+8+6+4+5+5)/10
= 6.31 μm
Result
The middle large square is represented by the red square, the smaller square is represented by the yellow square.
Volume of small square = 0.2mm x 0.2mm x 0.1 mm
= 0.004 mm3
= 4 x 10-3 ml
Sum of cells in 10 small box = X cells
Average cells = total cells/10 = Y
Concentration of yeast cell = Y/ (4 x 10-6) ml
Discussion
Ocular micrometer is a glass disk that fits in a microscope eyepiece that has a ruled scale, which is used to measure the size of magnified objects.The physical length of the marks on the scale depends on the degree of magnification.
Conclusion
2.2 Neubauer Chamber
Introduction
Neubauer chambers are more convenient for counting microbes. The Neubauer is a heavy glass slide with two counting areas separated by a H-shaped trough. A special coverslip is placed over the counting areas and sits a precise distance above them.
Neubauer chamber remains the most common method used for cell counting around the world. This technical data sheet has been composed in order to help experienced, as well as non-experienced, researchers perform a proper cell counting using a Neubauer chamber or Hemocytometer. The principles described in this technical data sheet apply to any cell counting chamber, although the dimensions and volumes of each chamber may differ. The technical data sheet describes the best practices, applications, and recommendations when performing a cell count.
Materials
- Serial dilutions of bacteria cultures(yeast)
- Neubauer and coverslip
- 70% ethanol
- Sterile Pasteur pipettes
Objectives
- To calculate the concentration of cells per square
- To calculate the amount of cell in 1 square
- To find the average amount of cell per square
Methodology
- A drop of diluted yeast culture is added to the space between the coverslip and the counting chamber using sterile Pasteur pipette.
- The cells was rested for 1 minute.
- The cells are counted in the four corner and the center squares. The Neubauer and coverslip are cleaned using 70% ethanol.
Counting
- The chamber contains many grids, producing nine (9) major large squares
- For calculation purposes, only the middle large square is used.
- The middle large square has a size of 1 mm x 1 mm and a depth of 0.1 mm
- Inside the middle large squares, there are 25 smaller squares, each with the size of 0.2 mm x 0.2 mm
- 10 of these 25 smaller squares are randomly chose and the number of yeast cells in each of the squares are calculated.
- Average the number of cells per square
- Assuming the average number of cells = Z; 1 mm3 = 0.001 cm3; 1 cm3 = 1 mL
- Cell concentration = (250,000 x Z) cells/mL
Observation
A drop of yeast is put onto the hemocytometer and it is covered with a slip. The hemocytometer is then is put under the microscope. Lens is adjusted until a clear picture of cells on the hemocytometer is obtained. Cells then are counted per square in order to find the concentration of square by finding the total cell counts and the average amount. The average of concentration is obtained by using a formula stated below in the result.Result
Square of 0.25mm × 0.25mm
|
Number of count cell present
|
1
|
125
|
2
|
118
|
3
|
125
|
4
|
115
|
5
|
102
|
Average number of cell = total cell count / volume
Volume= 0.25mm × 0.25mm × 0.1mm
= 0.00625mm^3
1ml^3 = 1cm^3
0.00625mm^3 x (0.001cm^3 / 1mm^3) = 6.25x10^-6cm^3
6.25x10^-6cm^3 = 6.25x10^-6ml^3
Average number of cells = (125+118+125+115+102) / 6.25x10^-6ml^3
Discussion
- Hemocytometer is a thick glass microscope slide with a rectangular indentation that creates a chamber. This chamber is consisting of grid of perpendicular lines.
- The area and the depth of the chamber is known so that the number of cells in a specific volume of fluid can be calculated.
- The principles of the calculation is, choosing 10 smaller squares out of 25, inside the middle large square. Calculate the number of yeast cells in each of the 10 squares, and then the average number of cells per squares.
The middle large square is represented by the red square, the smaller square is represented by the yellow square.
Volume of small square = 0.2mm x 0.2mm x 0.1 mm
= 0.004 mm3
= 4 x 10-3 ml
Sum of cells in 10 small box = X cells
Average cells = total cells/10 = Y
Concentration of yeast cell = Y/ (4 x 10-6) ml
Conclusion
The cell populations can be measured by counting the number of cells in smaller squares and the volume of suspension is equal to the area of smaller square times the depth of film. By using Neubauer Chamber, we can easily calculate the concentration of microorganisms or cells which have an average number of cells in 10 boxes divided by volume of suspension.