Biology Microscope Quiz

Focusing the Microscope

• Parfocal microscopes allow the object to remain nearly in focus when switching between objective lenses.
• Always find the object using the low-power objective before switching to the high-power objective.

Field of View

• Field of view is the circular area visible through the microscope's eyepiece.
• The field of view decreases as magnification increases.

Measuring Cell Size

• Use a ruler to measure the diameter of the field of view in millimeters when using the low-power objective.
• Convert millimeters to micrometers.
• Divide the field of view diameter by the number of cells that fit across the diameter to calculate the size of a single cell.

Longitudinal vs. Cross Section

• A longitudinal section is a cut through the long axis of an organ.
• A transverse section (cross section) is a cut along a horizontal plane that divides the organ into superior and inferior parts.

Resolution

• The resolution of a lens refers to its ability to distinguish between two closely positioned objects.
• Shorter wavelengths of light provide higher resolution.
• The limit of resolution for a visible light microscope is ~300nm with air and ~200nm with oil immersion.
• Ultraviolet light microscopy can achieve ~100nm resolution due to its shorter wavelength.

Fluorescent Proteins & Stains

• Red fluorescent protein (RFP) and green fluorescent protein (GFP) allow for the visualization of specific proteins or structures within cells.
• DAPI is a fluorescent stain that binds to adenine-thymine rich regions in DNA.

Confocal Microscopes

• Laser scanning confocal microscopes (LSCM) use a laser to scan the specimen point by point, creating optical sections.
• A pinhole filter eliminates unwanted fluorescence from above and below the focal plane.
• Confocal microscopy allows for the imaging of structures at specific depths within intact biological specimens.

Electron Microscopes

• Electron microscopes use a beam of electrons to provide high magnification and resolution.
• They are capable of visualizing much smaller objects than light microscopes.
• Transmission electron microscopes (TEM) provide 2D images similar to a compound light microscope.
• Scanning electron microscopes (SEM) provide 3D images similar to a dissecting microscope.
• Extensive specimen preparation is required for electron microscopy, which can introduce artifacts.

Microscope Use

• Keep both eyes open while viewing through the microscope.
• Begin and end microscope use with the lowest power objective.
• Do not clean lenses with regular paper tissues.
• Do not tilt the microscope.
• Do not remove microscope parts.
• Locate small objects in the slide first by eye or under low power before switching to higher magnifications.

Focusing the Microscope

• Always start with the scanning power objective (4x).
• Lower the stage using the coarse adjustment knob.
• Place the slide on the stage, secure with a clip, and view through the eyepiece.
• Slowly raise the stage with the coarse adjustment knob to bring the object into view.
• Use the fine adjustment knob to sharpen the focus.

Microscope Parts and Function

• The microscope is composed of various parts that work together for image formation.

Lenses and Magnification

• The total magnification is calculated by multiplying the objective lens magnification by the ocular lens magnification.

Microscope Immersion Oil

• Immersion oil is used with higher magnification lenses to improve resolution by increasing the light passing through the specimen.
• Make sure the objective lens is an oil immersion lens before using immersion oil.

Stereomicroscope

• Stereomicroscopes are used to observe the surfaces of large specimens and provide 3D information.
• They are also used for micromanipulation and dissections.
• External light sources at different angles can improve contrast and depth perception.
• Stereomicroscopes are versatile due to the availability of various objectives and eyepieces.