Microscopy Honor

Science & Health

Requirements

  1. Write an essay of at least 500 words about the history of microscopes.

    Answer: Janssen (1590) built the first compound microscope. Leeuwenhoek (17th century) with 270x discovered microorganisms. Hooke (1665) coined 'cell' in Micrographia. Zeiss and Abbe (19th century) revolutionized optics. Ruska (1931) invented the electron microscope and Binnig/Rohrer (1981) the atomic force microscope. — The essay must cover 4 milestones: 1) the Dutch origin (Janssen) and the first compound microscope; 2) Leeuwenhoek perfecting single lenses and seeing 'animalcules' (bacteria/protozoa); 3) Hooke publishing 'Micrographia' describing cork sections with 'cells'; 4) the industrial leap of Zeiss/Abbe (apochromatic objectives, condenser) in the 19th century; 5) the modern era: Ernst Ruska (1931) winning the Nobel for the electron microscope, with a magnification of 1,000,000x; 6) Binnig and Rohrer (Nobel 1986) developing the STM and AFM, reaching the atomic scale.

  2. Know the microscopes below, identifying them in person or through pictures and photos. State the main characteristics of each one.
    • Optical microscope
    • Scanning electron microscope
    • Transmission electron microscope
    • Atomic force microscope

    Answer: 1) Optical microscope: uses glass lenses and visible light to magnify the image; reaches up to about 1500x and allows observation of cells, tissues, protozoa and bacteria. It is simple, low-cost and works with living or fixed samples. 2) Scanning electron microscope (SEM): uses an electron beam that scans the surface of the sample (coated with metal), generating three-dimensional images with great depth and relief detail, with a magnification far superior to the optical one. 3) Transmission electron microscope (TEM): makes the electron beam pass through an ultra-thin sample, producing two-dimensional images of very high resolution; it reveals internal structures such as viruses and cellular organelles. 4) Atomic force microscope (AFM): has a fine tip (cantilever) that scans the surface measuring the atomic forces of interaction; it generates three-dimensional images at the atomic scale, without the need for a vacuum and being able to analyze samples in conditions close to natural ones. — Each technique has a distinct application. The optical (compound) microscope is the most common, with resolution limited by the wavelength of visible light (~200 nm). SEM (Scanning Electron Microscope) scans the surface with an electron beam, generating topographic images in 3D, magnification 100-100,000x. TEM (Transmission EM) passes through ultra-thin slices of tissue (sections of 50-100 nm), reaching up to 1,000,000x and the atomic level. AFM (Atomic Force Microscope) uses a cantilever with a silicon tip to feel atoms, seeing the sub-nanometer scale in a liquid medium or in air.

  3. Be able to identify the following parts of a microscope and explain and demonstrate the function of each one: eyepiece, objective, nosepiece (revolver), stage, condenser, base, focus (fine adjustment screw and coarse adjustment screw) and arm.

    Answer: Eyepiece: the lens at the eye (10x). Objective: the lens near the sample (4x-100x). Nosepiece: the rotating part holding the objectives. Stage: where the slide rests. Condenser: concentrates light. Base: the lower support. Coarse adjustment: rough focus. Fine adjustment: fine focus. Arm: connects the base to the optical part. — The compound optical microscope follows a standard arrangement. Eyepiece: the upper tube with a 10x lens. Objectives on the nosepiece: 4x panoramic, 10x intermediate, 40x detail, 100x oil immersion. The stage has a mechanical carriage to move the slide in XY with clips. The condenser (beneath the stage) with an iris diaphragm adjusts the light intensity. The coarse adjustment moves large distances, the fine adjustment focuses submillimetrically. The arm supports the weight and is the carrying handle. The base houses the lamp and the power source. Knowing the parts is a prerequisite for any practice.

  4. Know how to calculate the magnification on a compound optical microscope. Calculate the magnification of the microscope you are using for this honor.

    Answer: Total magnification = eyepiece magnification × objective magnification. Example: a 10x eyepiece and a 40x objective result in 400x (10×40). Switching to a 100x objective (immersion), the magnification will be 1000x. The values are engraved on the lenses themselves (eyepiece usually 10x; objectives at 4x, 10x, 40x and 100x). Just multiply to obtain the real magnification of what is observed in the sample. — Compound microscopes have two optical systems in series: the objective forms a magnified real image inside the tube, and the eyepiece magnifies that image again for the eye. The multiplication of the magnifications is the basic rule. Typically, eyepieces come in 10x or 15x; objectives in 4x (panoramic), 10x, 40x (high-resolution 'dry') and 100x (oil immersion). The practical limit is ~1500x before the diffraction of visible light degrades the image. For the requirement, the Pathfinder must read the engravings on the lenses of their own microscope and calculate.

  5. Define the following microscopy terms:
    • Slide
    • Coverslip
    • Wet mount examination (or direct examination or fresh examination)
    • Fixative
    • Stains
    • Immersion oil

    Answer: 1) Slide: a rectangular glass plate on which the sample to be observed is placed. 2) Cover slip: a small, thin, square (or rectangular) piece of glass placed over the sample, to protect it, flatten it and allow focusing. 3) Fresh direct examination (direct examination or wet mount): immediate observation of the material under the microscope, without fixation or staining, allowing one to see structures and the movement of living organisms. 4) Fixative: a solution that preserves and hardens tissues and cells, maintaining their structure for analysis (e.g.: formalin, alcohol). 5) Stains: substances that give color and highlight structures, facilitating visualization (e.g.: methylene blue, eosin, Lugol's iodine). 6) Immersion oil: oil placed between the slide and the 100x objective; because it has a refractive index similar to that of glass, it reduces light loss and increases the resolution of the image. — These are basic terms of laboratory routine. Slides (microscope slides) measure 76x26 mm. Cover slips cover the sample, preventing contact with the objective. A wet mount preserves cellular movement (useful for protozoa). Fixatives (10% formaldehyde, 70% ethanol) halt vital processes. Stains: methylene blue highlights nuclei; eosin highlights the cytoplasm; hematoxylin+eosin is the pathology standard (H&E). Immersion oil has a refractive index close to that of glass, avoiding light loss, allowing 100x objectives to reach 0.2 µm of resolution.

  6. Collect water samples (from ponds, streams, rivers, lakes, puddles), prepare them correctly and look for microorganisms using a microscope with at least 100x magnification. Draw 5 of these organisms with as much accuracy as possible. In the drawing, label the identified structures (including the magnification used).

    Answer: Collect water from ponds, rivers or puddles in a clean container. Drop a drop onto the slide, cover with a cover slip and observe under the microscope at at least 100x. Identify and draw 5 microorganisms (such as paramecia, amoebas, rotifers, algae, bacteria), labeling the visible structures (cilia, nucleus, vacuoles, flagella) and the magnification used in the observation at the end. — Still waters (ponds, puddles) are rich in protists and algae. Materials: pipette, slides, cover slips, microscope. Technique: drop a drop, cover with a cover slip at an angle (avoids bubbles), observe starting with the 4x, then 10x and 40x. For 100x use immersion oil. Common organisms: Paramecium (cilia), Amoeba (pseudopods), Euglena (flagellum + chloroplasts), Volvox (colony), Spirogyra (filamentous alga), rotifers. Draw faithfully, with proportions and visible structures. Note the total magnification next to the drawing.

  7. Cite at least one example of how microscopy is important for:
    • Human nutrition
    • Human health
    • Medications
    • Other organisms

    Answer: 1) Human food: microscopy makes it possible to detect fungi, molds, yeasts and contamination in foods (cheese, bread, grains), verify the quality of milk and identify adulterations and impurities. 2) Human health: it is essential for the diagnosis of parasites, the counting and analysis of blood cells, urine and stool tests, the identification of bacteria and the reading of biopsies and cytological exams. 3) Medicines: used in pharmaceutical research, in the quality control of active ingredients, in verifying purity and in analyzing the structure of crystals and formulations. 4) Other organisms: it reveals the microbial biodiversity of the soil and water, the plankton of aquatic ecosystems, the yeasts used in fermentation and the cell structure of plants and animals. — Microscopy has a cross-cutting application. Food: it identifies Saccharomyces cerevisiae (bread, beer), Penicillium (cheeses), as well as pathogenic contaminants. Health: blood count, parasitology (Giardia, Plasmodium of malaria), histopathology (cancer biopsies), Pap smear (cervical cancer). Medicines: validation of purity, research of new molecules, electron microscopy of drugs. Biology: microbial ecology, marine plankton as the base of the food chain, the human intestinal microbiome with 100 trillion bacteria.

  8. Cite at least three health habits that were established as a direct result of the harm from microcellular organisms that became evident after the discovery of microscopes. Put these habits into practice.

    Answer: Washing the hands with soap (combats bacteria and viruses). Boiling/filtering drinking water (eliminates parasites such as Giardia and bacteria such as Vibrio cholerae). Pasteurization of milk and foods (kills pathogens without altering quality). Others: washing fruits and vegetables, covering food, vaccination, sterilization of medical instruments and isolation of contagious patients. — Microbiology transformed modern medicine. Joseph Lister (1867) introduced antiseptics in surgery after Pasteur saw bacteria. Ignaz Semmelweis (1847) proved statistically that washing hands lowered puerperal mortality. Pasteurization (1864) saved lives in dairies. John Snow (1854) identified cholera from contaminated water in London with an epidemiological 'microscope'. Modern habits descend from these discoveries: vaccination (Jenner/Pasteur), antibiotics (Fleming, 1928), autoclave sterilization. The Pathfinder must adopt at least three as a daily practice.