INTRODUCTION TO THE BIOLOGY LAB

 

This lab period you will learn how to use the light and dissecting microscopes to examine a variety of items.  You will make wet mounts and a bacterial smear. You will also be able to examine a variety of prepared slides.

 

 

USE OF THE LIGHT MICROSCOPE

 

Identify the following parts of the light microscope and give its function:

 

Ocular lens

Body tube

Arm

Nosepiece

Scanning power objective

Low power objective

High power objective

Oil immersion objective

Stage

Coarse adjustment knob

Fine adjustment knob

Illuminator

Iris diaphragm

Condenser

 

 

 

PROCEDURE

 

A.                                    Clean lenses, condenser and illuminator with lens paper and lens cleaner.

B.                                     Using the coarse adjustment knob, lower the stage as much as you can.

C.                                     Place a slide on the stage and anchor it with the stage clips.

D.                                    Move the scanning objective over the slide and slowly move the stage up towards the objective until the

     object comes into view.

E.                                     Use the fine adjustment knob to sharpen your focus if needed.

F.                                     Center the slide in your center of view.

G.                                     Carefully move the 10x objective over the slide.  Adjust your focus with the fine adjustment knob

      ONLY.

H.                                    Center the slide in your field of view and carefully move the 40x lens over the slide. Adjust your focus

      with the fine adjustment knob ONLY.

I.                                       When you are finished, move the stage down and move the scanning objective back in place.

 

 

 

CALCULATING MAGNIFICATION

 

Unless stated otherwise the ocular of a microscope is always 10x.  The magnification is always obtained by multiply the power of the ocular by the power of the objective.

 

Figure the total magnification of your scanning, low power, high power and oil objectives.

 

 

 

DETERMINING DIAMETER OF FIELD OF VIEW

 

PROCEDURE

 

A.                           Place a plastic rule across the microscope stage so its edge can be seen as a vertical line across the diameter across the low power field.

B.                            Using the millimeter markings measure the field of view.

C.                            Repeat this process with the 10x and 40x objectives

 

 

OBSERVATIONS WITH THE MICROSCOPE --- PREPARED SLIDES

 

 

A variety of slides are available in the back of the room.   Examine 10 prepared slides under the microscope and draw what you see.

 

OBSERVATIONS WITH THE MICROSCOPE --- PREPARATION OF WETMOUNTS

 

1.             Using a disposable pipette place about 0.1 ml of pond water onto your slide.  You want to have a drop large to ensure the space between the coverslip and slide will be full but small enough that it will not spill out.  You may gently blot any excess material off with paper toweling if necessary. 

 

3.             Hold the coverslip by its edges and draw it along the slide from the far edge until it touches the water drop.  Allow the coverslip to drop onto the slide. 

 

4.                     Observe your slide under the microscope. 

 

5.                           Examine four pond samples and draw what you see.

 

 

 

USE OF THE DISSECTING MICROSCOPE

 

Identify the following parts of the dissecting microscope:  binocular eyepiece, focusing knob, arm, magnification control knob, base, stage and light source.

 

 

PROCEDURE

 

A.                           Set up your dissecting microscope and light source.

B.                            Place a coin in the center of the stage.

C.                            Focus and observe the coin under a variety of magnifications.

D.                           Change the magnification of the scope.

E.                            Obtain five of the objects available at the back of the room to examine.

 

YOU DO NOT HAVE TO DRAW ANY OF THESE OBJECTS.

 

OBSERVATIONS WITH THE MICROSCOPE --- PREPARATION OF A BACTERIAL SMEAR

 

You will prepare a bacterial smear.  Before beginning be sure to:

 

 1                                    Clean lenses, condenser and illuminator with lens paper and lens cleaner.

 

2                                           You will be given a bacterial smear that has already been heat fixed.

 

3                                           Cover the smear with crystal violet stain for one minute.

 

4                                           Quickly wash off the stain using the bottle of distilled water.  Shake off excess water.

 

5                                           Cover the smear with Gram’s iodine for one minute.

 

6                                           Shake off the Gram’s iodine.

 

7                                           Rinse  the smear with 95% Ethanol until the runoff is clear.

 

8                                           Rinse the Ethanol off with water.

 

9                                           Cover the smear with safranin for one minute.

 

10                                        Rinse the smear with water for 10 seconds.

 

11                                        Blot the smear with paper toweling and let it air dry. 

 

12                                        Draw what you see under 40x