Lab 2 Report written by Tan Hwee Feng

Name: Tan Hwee Feng
Matric No: 111427

2.1 Ocular Micrometer

Introduction

Ocular micrometer is use in order to measure and compare the size of prokaryotic and eukaryotic microorganisms. Microorganisms are measured with an ocular micrometer which is inserted into the one of the microscope eyepieces. The micrometer, which serves as a scale or rule, is a flat circle of glass upon which are etched equally spaced divisions. This is not calibrated, and may be used at several magnifications. When placed in eyepiece, the line superimposed certain distance markers on the microscope field. The actual distance superimposed may be calibrated using a stage micrometer on which parallel lines exactly 10micrometer apart etched. By determining how many units of the ocular micrometer superimpose a known distance on the stage micrometer. You can calculate the exact distance each ocular division measures on the microscopic field. When you change objectives you must recalibrate the system. After calibration of the ocular micrometer, the stage micrometer is replaced with a slide containing microorganisms. The dimensions of the cells may then be determined.

Objective

To measure and count cells using a microscope.

Results

Total magnification = objective lens power x eyepiece lens power(10x)



Yeast under 400x magnification:

 

2.5 micrometer x 2 = 5 micrometer

 Yeast under 1000x magnification:

                                                    1.0 micrometer x 5 = 5 micrometer

Lactobacillus under 1000x magnification:

 1.0 micrometer x 2.5 = 2.5 micrometer

Discussions

1) The ocular micrometer is simply a glass disc with etched lines on its surface.The distance between

graduations of an ocular micrometer does not have any standard value.

2) The distance is worked out by calibrating it with a known scale, stage micrometer.

3) Stage micrometer is a special glass slide which have a known distance. One division of stage micrometer = 0.01 mm.

4) One ocular division =   no. of divisions on stage micrometer 

                                          no. of divisions on ocular micrometer

5) For 400x magnification:

     Stage scale = 0.01 mm x 5 divisions

                        = 0.05 mm

     one ocular division  = 0.05 mm/20 divisions on ocular micrometer

                                      = 0.0025 mm

                                      = 2.5 micrometer

    Average dimensions of sample yeast cells  = 2.5 micrometer x 2 ocular divisions 

                                                                         = 5.0 micrometer

   

6) For 1000x magnification:

     Stage scale = 0.01mm

     one ocular division = 0.01 mm/10 divisions on ocular micrometer

                                     = 0.001 mm

                                     = 1.0 micrometer

     Average dimensions of sample yeast cells = 1.0 micrometer x 5 ocular divisions

                                                                         = 5.0 micrometer

     Average dimensions of sample lactobacillus cells = 1.0 micrometer x 3 ocular divisions

                                                                                     = 3.0 micrometer

Conclusion

      Ocular micrometer has a measurement scale that allows the us to measure the size of magnified objects. A special slides which contains scales also used to place the objects being observed. Besides that, this experiment also allow us to learn how to calculate the dimensions of cells using stage micrometer and ocular micrometer. By learning this method, microorganisms or cells such as yeast and lactobacillus can be measured and the size can be compared. 

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References

 

http://www.ehow.com/how_5019336_use-ocular-micrometer.html

http://www.doctorfungus.org/thelabor/sec11.pdf

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.

Objective

To measure and count cells using a microscope

Results

Yeast under 400x magnification: 

 

11	8
12			9
		14	8
8	11	9	5

Discussions

1) A device used for determining the number of cells per unit volume of a suspension is called a counting chamber (Neubauer Chamber).
2) Inside the middle large squares, there are 16 smaller squares, each with the size of 0.2mm x
 0.2mm.
3) We randomly choose 10 of these 16 smaller squares and calculate the number of yeast cells in each of the squares.
4) Volume of small square = 0.2mm x 0.2mm x 0.1 mm
                                           = 0.004 mm^3
                                           = 4 x 10^-6 mL
     Sum of cells in 10 small box = 95 cells
     Average cells = 95 cells/ 10
                            = 9.5
     Concentration of yeast cell = 9.5 cells / (4 x 10^-6) mL
                                                 = 2.375 x 10^6 cells/mL

Conclusion

The number of cells in a population can measured by counting the number of cells in smaller squares and the volume of suspension is equal to area of smaller square times depth of film.With using Neubauer chamber, we can easily calculate the concentration of microorganisms or cells which is average number of cells in 10 box divide by volume of suspension.

References

http://b110-wiki.dkfz.de/signaling/wiki/display/rnaiwiki/Counting+cells+with+haemocytometer+%28Neubauer+chamber%29
http://www.emsdiasum.com/microscopy/products/magnifier/counting.aspx
http://www.ruf.rice.edu/~bioslabs/methods/microscopy/cellcounting.html