Laboratory Exercise 02 Use of Microscope in Marine Biology

INTRODUCTION

            Living microorganisms may be visualized either by wet film or as stained film in order to determine their size, shape and whether they are motile or not, how they divide and whether or not they produce spores or granules. Wet films are generally used to study living microorganisms. A hanging drop, a variation of the wet mount, allows for some extended observations of the microbial population in more or less natural environment. Although much can be learned

Although much can be learned from observing unstained microorganisms, the addition of colored substances can reveal structures that are invisible in unstained preparations. Staining techniques are used routinely to differentiate among major groups of microorganisms to detect chemical and structural differences in bacterial cell walls and to observe specific cellular components. Stained films are examined under oil immersion objectives and it is essential to set-up the microscope carefully. Time spent will be amply repaid. Failure to do this will result in inability to carry out of the work satisfactorily. The principle of lighting in both preparations differs. Refraction is involved in obtaining structure image in wet mounts while in stained preparation is absorption.

OBJECTIVES

1. To visualize bacteria in wet and stained preparations.
2. To put into practice the techniques of preparing wet mounts.
3. To present an important aspect in the study of bacteria. 

METHODOLOGY

1. Preparation of wet films. Place a drop of plankton culture on a microscope slide. Lower a cover slip on the drop to spread it. Examine it under low power. Adjust the iris diaphragm to allow small amount of light. Swing to 40x (high -power dry lens). Lower the condenser to provide weak general illumination and partially close the iris diaphragm to cut down peripheral rays. Observe for the motility of organism. Excessive illumination renders the organism invisible.
2. Examination of Stained films:  i.    Staphylococcus aureus     ii.    Escherichia coli    iii.    Bacillus subtilis    
3. Carefully dust and clean all optical parts with a soft clean cloth moistened with little xylene. Do not use acetone or alcohol for this purpose.      
4. Condenser. See that the condenser is raised to its upper limit in its fitting. Open diaphragm fully. Place a prepared slide on stage and rack up condenser until it almost touches the slide.   
5. Oil-immersion objective. Scan the slide with 10x objective until a suitable area of investigation is centrally placed in the field   
6. Place a drop of oil immersion on the dry film and switch to the oil immersion objectives. Swing the objective into the oil carefully watching at the side using the coarse adjustment, until the object comes into view. Use the fine adjustment to secure sharp definition. It may be necessary to raise or lower the condenser very slightly at this stage to secure optimum illumination.
7. Clean off oil after use. Dried oil on the objectives is an indication of the carelessness of the previous user. 

RESULTS AND DISCUSSION:

Guide Questions:

1. When is the use of wet mount very convenient? Stained preparation? Give the pros and cons of using each preparation

 REFERENCES:

LABORATORY EXERCISE 2

  

                                     Use of microscope in marine biology

	Name: Date Performed Rating:

 

 RESULTS    

Draw the microorganisms you have observed in the wet mounts and indicate their sizes and shapes. Record the actual size and magnification in your drawing.

1. Draw the types of microorganisms seen under high dry magnification. Indicate their relative size and shapes 

    and arrangements.

REFERENCES