Introduction to BiologyIntroduction to BiologyIntroduction to BiologyIntroduction to Biology

Biology

• The word biology means the study of life.  Translated from Greek:

• Bios means “life” • Ology means “the study of” or “the science of”. 

The Microscope

The MicroscopeThe MicroscopeThe MicroscopeThe Microscope

Types of Microscopes• Compound Microscopes

• Light illuminated. • Image seen with this type of microscope is two

dimensional. • Is the most commonly used. You can view

individual cells, even living ones. It has high magnification. However, it has a low resolution.

• A dissection microscope• Is light illuminated. • The image that appears is three dimensional. • It is used for dissection to get a better look at

the larger specimen. You cannot see individual cells because it has a low magnification

Eyepiece

Body Tube

Revolving NosepieceArm

Objective Lens

StageStage Clips

Coarse Focus

Fine Focus

Base

Diaphragm

Light

• Eyepiece Lens:  the lens at the top that you look through.  They are usually 10X or 15X power. 

• Tube:  Connects the eyepiece to the objective lenses

• Arm:  Supports the tube and connects it to the base

• Base:  The bottom of the microscope, used for support

ArmRevolving Nose Piece

• Stage:  The flat platform where you place your slides.  Stage clips hold the slides in place.  If your microscope has a mechanical stage, you will be able to move the slide around by turning two knobs.  One moves it left and right, the other moves it up and down.

• Stage clips: Metal clips that hold a slide securely onto the stage.

• Revolving Nosepiece or Turret:  This is the part that holds two or more objective lenses and can be rotated to easily change power.

• Objective Lenses:  Usually you will find 3 or 4 objective lenses on a microscope. They are found on the revolving nosepiece. 

• They almost always consist of 4X, 10X, 40X and 100X powers. 

• The shortest lens is the lowest power, the longest one is the lens with the greatest power. 

• Illuminator:  A steady light source used in place of a mirror.  If your microscope has a mirror, it is used to reflect light from an external light source up through the bottom of the stage.

• Diaphragm or Iris:  Many microscopes have a rotating disk under the stage. 

• This diaphragm has different sized holes and is used to vary the intensity and size of the cone of light that is projected upward into the slide. 

• There is no set rule regarding which setting to use for a particular power.  

• Fine focus adjustment: A knob that makes small adjustments to the focus (it is often smaller than the coarse focus knob)

• Coarse focus adjustment: A knob that makes large adjustments to the focus

Handle and Care of a Microscope

• Carry the microscope with two hands. Keep one hand underneath the microscope and the other on the arm. The biggest reason microscopes break is not because they wear out, but because they are dropped.

• Never touch any lens with your fingers. This leaves oil which is hard to clean and particles which may damage the lens. If a lens needs cleaning, use lens tissue, a lens cloth or a lens pen and be gentle. Do not use your shirt or a towel.

• Obtain a slide and place it on the stage of the microscope. Secure the slide with the stage clips.

• Rotate the objectives on the nosepiece of the microscope until the shortest objective is over the slide and make sure the objective clicks into place. The shortest objective is LOW power. ALWAYS START WITH THE LOW POWER OBJECTIVE!

• Low power lens gives the widest field of view and makes it easier to find the specimen when you look through the microscope. Finding the specimen at high power, without first centering it in the field of view at low power, is nearly impossible.

• Open the iris if your microscope has an iris or rotate the diaphragm (circular plate under the stage with different size holes) until one of the large holes is centered under the slide. This is your light control.

• Start with plenty of light, but once you have focused and found your specimen in the field of view, start reducing light until you see the most amount of detail.

• The brightest setting is typically not the best for contrast and detail.

• Focus slowly. It is easy to focus right past the correct focus point if you are going too fast.

• Use the coarse adjustment for low and medium power and fine tune with the fine focus knob as needed.

• Rotate to the objective that has the medium length over the slide and be sure it clicks into place. Refocus, but slowly. You will only be seeing a part the specimen.

• Move the slide slowly back and forth if you cannot see anything. If you get lost and lose the specimen, go back to low power, center the slide and try again. It may take several tries to find a specimen, but this is normal.

• If you managed medium power and have the specimen focused and in the field of view, you can try high power.

• Once again, center the specimen in the field of view and slowly and carefully rotate the longest tube objective (high power) until it clicks into place. It will barely clear the slide, so be careful.

• The next rule is very important. DO NOT USE COARSE FOCUS ON HIGH POWER EVER! If your microscope has both fine and coarse focus, use only fine focus at high power.

• Why? The objective is very close to the slide, now. If you use coarse focus, you can jam the objective down onto the slide and break the slide. Worse, yet, you may soil and even damage the objective.

• You will soon discover that using the microscope at high power is much more difficult than at low power. It takes practice!

• The good news is that you do not need high power that often. Most of the things you are going to study with a microscope look better at low and medium power, anyway. Even scientists use low and medium powers for much of their work. Use only enough magnification as needed.

• Have fun with your microscope. There's a whole other world waiting for you to see!

• Microscope activity• Obtain a microscope (following the rules for

handling and care).• Obtain a prepared slide.• Follow the steps for viewing a specimen under

low, medium and high power.• Show your teacher once you have focused

your specimen with each objective lens.