Microscope Use and Components

Microscope Basics

• Microscopes are used to observe objects too small to see with the naked eye.
• Proper microscope handling involves grasping the arm with one hand and supporting the base with the other.
• The mechanical stage is the platform where microscope slides are placed.
• The path viewed goes through the ocular or eyepiece, then through the lens of the objective.
• Compound microscopes typically have binocular eyepieces and multiple objectives: scanning (4x), low power (10x), and high power (40x).
• The condenser focuses light onto the slide, while the iris diaphragm regulates the amount of light.
• Major adjustments are done with the coarse adjustment knob, minor with the fine adjustment knob.
• The rheostat adjusts the intensity of light, and the iris diaphragm can also influence light levels.

Resolution and Magnification

• Resolution describes the ability to distinguish between closely spaced points.
• High resolution results in a sharp image.
• Human eye's resolution is about 0.1 mm.
• Shorter light wavelengths, like blue light, enhance resolution.
• Best compound microscopes have a resolution of about 0.2 µm.
• Opening the iris diaphragm can increase resolution but may reduce contrast.
• Magnification is how much larger an object appears compared to its actual size.
• Total magnification is the product of the ocular and objective lens powers (e.g. 10X ocular and 10X objective yield 100X magnification).
• Excessive magnification beyond the resolution limit does not improve clarity

Experimental Design

• Experimental design is how one tests a hypothesis through experimentation.
• A strong design yields reliable conclusions about cause-and-effect relationships.
• Experiments involve independent, dependent, and controlled variables.
• The independent variable is what the researcher changes.
• The dependent variable is affected by changes in the independent variable.
• Controlled variables remain constant to ensure the change is only due to the independent variable.
• A control group does not receive the experimental treatment.
• Charts and graphs help to represent data.
• Typically, independent variables are on the x-axis and dependent variables on the y-axis.
• Continuous independent variables are suited to scatter plots, while discrete variables are suited to column charts.

Leaf Stomata

• Plants exchange gases via stomata for photosynthesis
• Stomata are surrounded by guard cells
• When guard cells are turgid (filled with water), the stoma opens
• Open stomata allow plants to exchange CO2 and O2
• When guard cells are flaccid, stomata close
• Closed stomata reduce water loss and also gas exchange

Microscope Usage

• Clean microscope lenses with lens paper moistened with water.
• Start observations with the scanning objective (4x).
• Adjust the stage using the coarse adjustment knob.
• Adjust the interpupillary distance using the knob between the oculars.
• Focus each eyepiece separately to correct for vision differences.
• Note the adjustment on the ocular for future ease of use.
• When moving the slide left, the image moves to the right and vice versa
• Microscopes should be parfocal, in focus with low power and almost in focus with higher power.
• You can bring the object into focus using only the fine adjustment.
• As magnification increases, the field of view and working distance decrease and image brightness decreases.
• Adjust rheostat or iris diaphragm for light as magnification increases.
• The depth of field decreases at higher powers.
• Locate objects under the lowest power before increasing magnification.

Wet Mounts and Dissecting Scopes

• Wet mounts involve placing a liquid drop on the slide, adding the specimen, and covering with a coverslip.
• The cover glass should be lowered at an angle to prevent bubbles
• Depth of field is the vertical distance that remains in focus at one time
• Dissecting microscopes use reflected light.
• Dissecting microscopes have a larger depth of field.

Stomata Experiment

• Use nail polish to make a cast of cells from a leaf
• Apply nail polish to dry section of the leaf
• Use tape to peel off for the sample leaf cast for viewing
• Count all stomata that are at least half visible
• Stomata are considered open if guard cells are turgid
• Repeat the count at least 3 times per sample
• Use excel to do an experimental design and data presentation
• Ensure to correctly store away microscope to avoid point deuductions

Learn about the parts of a compound microscope, including the eyepiece, objectives, stage, and focusing knobs. Understand proper handling techniques and the function of the condenser and iris diaphragm. Explore concepts of magnification and resolution in microscopy.