How se see the invisible world

• The first step is to recognize that we are not alone.
• Visible light consists of electromagnetic waves.
• Amplitude is the height of each peak (or depth of each trough) in a wave.
• Wavelength is the distance between one peak of a wave and the next peak.
• Frequency is the rate of vibration of the wave, or the number of wavelengths within a specified time period.
• Reflection occurs when a wave bounces off of a material.
• Absorption occurs when a material captures the energy of a light wave.
• Transmission occurs when a wave travels through a material, like light through glass.
• Transmittance is the process of transmission through a material.
• Light waves can also interact with each other by interference, creating complex patterns of motion.
• Diffraction is the phenomenon where light waves can bend or scatter when they interact with small objects or openings.
• Refraction is the change in speed and direction of light waves as they enter a new medium.
• The refractive index of a material is the extent to which it slows transmission speed relative to empty space.
• When light crosses a boundary into a material with a higher refractive index (like a lens), its direction turns to be closer to perpendicular to the boundary (i.e., more toward a normal to that boundary).
• A lens is an object with a curved boundary (or a collection of prisms) that collects all of the light that strikes it and refracts it so that it all meets at a single point called the focal point.
• A convex lens can be used to magnify because it can focus at closer range than the human eye, producing a larger image.
• Concave lenses and mirrors can also be used in microscopes to redirect the light path.
• The focal point is the image point when refracted light meets at a single point.
• The focal length is the distance to the focal point for convex and concave lenses.
• The different types of EMR fall on the electromagnetic spectrum, which is defined in terms of wavelength and frequency.
• Waves with higher frequencies have shorter wavelengths and, therefore, have more oscillations per unit time than lower-frequency waves.
• Higher-frequency waves also contain more energy (deliver more photons) than lower-frequency waves (deliver fewer photons).
• Photons are the elemental package of light energy.
• In the spectrum of visible light, each color corresponds to a particular frequency and wavelength.
• Stains, or dyes, contain salts made up of a positive ion and a negative ion.
• Chemical fixatives are often preferable to heat for tissue specimens.
• Some staining techniques involve the application of only one dye to the sample; others require more than one dye.
• Differential staining distinguishes organisms based on their interactions with multiple stains.
• There are scenarios in which it is advantageous to use a negative stain, which is absorbed by the background but not by the cells or organisms in the specimen.
• If the negative ion is the chromophore, the stain is considered an acidic dye.
• Negative staining produces an outline or silhouette of the organisms against a colorful background.
• In most cases, it is preferable to use a positive stain, a dye that will be absorbed by the cells or organisms being observed, adding color to objects of interest to make them stand out against the background.
• Gram Staining is a differential staining procedure that involves multiple steps.
• Chemical agents such as acetic acid, ethanol, methanol, formaldehyde (formalin), and glutaraldehyde can denature proteins, stop biochemical reactions, and stabilize cell structures in tissue samples.
• Gram's iodine, a mordant, acts like a trapping agent that complexes with the crystal violet, making the crystal violet-iodine complex clump and stay contained in thick layers of peptidoglycan in the cell walls.
• To heat-fix a sample, a thin layer of the specimen is spread on the slide (called a smear), and the slide is then briefly heated over a heat source.
• If the chromophore is the positively charged ion, the stain is classified as a basic dye.
• Depending on the type of dye, the positive or the negative ion may be the chromophore (the colored ion); the other, uncolored ion is called the counterion.
• Fixation kills microorganisms in the specimen, stopping their movement and metabolism while preserving the integrity of their cellular components for observation.
• Cells that have thick peptidoglycan layers in their cell walls are much less affected by the decolorizing agent; they generally retain the crystal violet dye and remain purple.