microlab.

Metric Units of Length and U.S. Equivalents

  • Metric Units: Standard measures of length used in the metric system.

    • Kilometer (km): 1 km = 1000 meters (m)

    • Meter (m): Basic unit of length.

    • Decimeter (dm): 1 dm = 0.1 m.

    • Centimeter (cm): 1 cm = 0.01 m.

    • Millimeter (mm): 1 mm = 0.001 m.

    • Micrometer (μm): 1 μm = 0.000001 m.

    • Nanometer (nm): 1 nm = 0.000000001 m.

    • Picometer (pm): 1 pm = 0.000000000001 m.

  • Meaning of Prefixes:

    • kilo: 1000

    • deci: 1/10

    • centi: 1/100

    • milli: 1/1000

    • micro: 1/1,000,000

    • nano: 1/1,000,000,000

    • pico: 1/1,000,000,000,000.

Ocular Lens and Microscope Parts

  • Ocular Lens (Eyepiece):

    • Remagnifies the image formed by the objective lens.

  • Body Tube:

    • Transmits the image from the objective lens to the ocular lens.

  • Arm:

    • Supports the microscope.

  • Objective Lenses:

    • Primary lenses that magnify the specimen.

  • Stage:

    • Holds the microscope slide in position.

  • Condenser:

    • Focuses light through the specimen.

  • Diaphragm:

    • Controls the amount of light entering the condenser.

  • Illuminator:

    • Light source for the microscope.

  • Coarse and Fine Focusing Knobs:

    • Adjust the focus to enhance clarity of the image.

Length Comparisons and Microscopy

  • Length of Organisms:

    • Human height: ~10 m

    • Length of some nerve/muscle cells: ~1 m

    • Chicken eggs: ~1 cm

    • Eukaryotic cells: ~10 µm

    • Most bacteria: 1 µm

    • Viruses: 100 nm.

  • Microscope Types:

    • Unaided Eye: seen size 10 m - 1 mm

    • Light Microscope (LM): used to view cells of length ~10 µm - 1 µm.

    • Electron Microscope: can view structures smaller than 0.1 nm.

Basic Light Microscopes

  • Brightfield Microscope:

    • Uses visible light; cannot resolve structures smaller than 0.2 μm; specimen appears against a bright background.

    • Uses: To observe stained specimens, count microbes.

  • Darkfield Microscope:

    • Uses opaque disc to block light directly; specimen appears light against a dark background.

    • Uses: To examine living microorganisms that are invisible in brightfield, does not stain easily.

  • Phase-Contrast Microscope:

    • Contains annular diaphragm; allows direct light through while focusing on the specimen for internal examination.

    • Uses: Detailed examination of living specimens without staining.

  • Differential Interference Contrast Microscope:

    • Utilizes differences in refractive indexes; produces images using two beams of light.

    • Uses: Provides three-dimensional images.

Advanced Light Microscopes

  • Fluorescence Microscope:

    • Uses UV or near-UV light to illuminate fluorescent microbes.

    • Uses: Rapid detection of microbes using fluorescent-antibody techniques.

  • Confocal Microscope:

    • Uses laser light to illuminate one plane at a time; focused imaging.

    • Uses: Obtains 2D and 3D images for biomedical applications.

  • Scanning Acoustic Microscope:

    • Uses sound waves; provides detailed views of internal structures.

    • Uses: Examine living cells, biofilms, cancer cells.

Electron Microscopes

  • Transmission Electron Microscope (TEM):

    • Uses electron beams to image structures smaller than 0.2 μm; produces 2D images.

    • Uses: To examine viruses and internal structures of cells.

  • Scanning Electron Microscope (SEM):

    • Uses reflective electrons; provides 3D imaging of surfaces.

    • Uses: Study surface features of microorganisms and cells.

Summary of Various Types of Stains

  • Simple Stains:

    • Highlight microorganisms for cellular shapes and arrangements.

  • Differential Stains:

    • Distinguish R type bacteria from G type (positive/negative).

  • Special Stains:

    • For structures like capsules, endospores, and flagella.