Skip to ContentGo to accessibility page
OpenStax Logo
Microbiology

Summary

MicrobiologySummary

Summary

2.1 The Properties of Light

  • Light waves interacting with materials may be reflected, absorbed, or transmitted, depending on the properties of the material.
  • Light waves can interact with each other (interference) or be distorted by interactions with small objects or openings (diffraction).
  • Refraction occurs when light waves change speed and direction as they pass from one medium to another. Differences in the refraction indices of two materials determine the magnitude of directional changes when light passes from one to the other.
  • A lens is a medium with a curved surface that refracts and focuses light to produce an image.
  • Visible light is part of the electromagnetic spectrum; light waves of different frequencies and wavelengths are distinguished as colors by the human eye.
  • A prism can separate the colors of white light (dispersion) because different frequencies of light have different refractive indices for a given material.
  • Fluorescent dyes and phosphorescent materials can effectively transform nonvisible electromagnetic radiation into visible light.
  • The power of a microscope can be described in terms of its magnification and resolution.
  • Resolution can be increased by shortening wavelength, increasing the numerical aperture of the lens, or using stains that enhance contrast.

2.2 Peering Into the Invisible World

  • Antonie van Leeuwenhoek is credited with the first observation of microbes, including protists and bacteria, with simple microscopes that he made.
  • Robert Hooke was the first to describe what we now call cells.
  • Simple microscopes have a single lens, while compound microscopes have multiple lenses.

2.3 Instruments of Microscopy

  • Numerous types of microscopes use various technologies to generate micrographs. Most are useful for a particular type of specimen or application.
  • Light microscopy uses lenses to focus light on a specimen to produce an image. Commonly used light microscopes include brightfield, darkfield, phase-contrast, differential interference contrast, fluorescence, confocal, and two-photon microscopes.
  • Electron microscopy focuses electrons on the specimen using magnets, producing much greater magnification than light microscopy. The transmission electron microscope (TEM) and scanning electron microscope (SEM) are two common forms.
  • Scanning probe microscopy produces images of even greater magnification by measuring feedback from sharp probes that interact with the specimen. Probe microscopes include the scanning tunneling microscope (STM) and the atomic force microscope (AFM).

2.4 Staining Microscopic Specimens

  • Samples must be properly prepared for microscopy. This may involve staining, fixation, and/or cutting thin sections.
  • A variety of staining techniques can be used with light microscopy, including Gram staining, acid-fast staining, capsule staining, endospore staining, and flagella staining.
  • Samples for TEM require very thin sections, whereas samples for SEM require sputter-coating.
  • Preparation for fluorescence microscopy is similar to that for light microscopy, except that fluorochromes are used.
PreviousNext
Order a print copy
Citation/Attribution
Reuse and redistribution of this content in digital or print format:
  • This book may not be used in the training of large language models or otherwise be ingested into large language models or generative AI offerings without OpenStax's prior written permission.
  • This book uses the Creative Commons Attribution-NonCommercial-ShareAlike License, which means that you can reuse and modify the material only for noncommercial purposes, must attribute OpenStax, and must distribute any derivative works under the same license.
  • Any commercial printing of this textbook, including using a local or custom printer, must be approved by OpenStax, and proper citation provided.
  • OpenStax-copyrighted images, activities, assessments, and similar components of this book are subject to the same licensing – CC-BY-NC-SA. They can be used for noncommercial purposes with attribution. Commercial use requires permission.
  • Permission requests: Anyone who intends to incorporate this content (including text, images, and other components) into large language models, use it in AI offerings, use it commercially (including in print), and/or has questions about another use case is welcome to complete our reuse request form.
Attribution information
  • If you are redistributing all or part of this book in a noncommercial print format, then you must include on every physical page the following attribution:

    Access for free at https://openstax.org/books/microbiology/pages/1-introduction

  • If you are redistributing all or part of this book in a noncommercial digital format, then for every page that includes OpenStax content, you must license the derivative work under the same CC-BY-NC-SA license as the original, and include on every digital page view the following attribution:

    Access for free at https://openstax.org/books/microbiology/pages/1-introduction

Citation information

The information below includes the information needed to generate citations in most major styles (APA, MLA, etc.); you must reformat and organize the information as needed to fit the requirements of the style. Use the information below to generate a citation. We recommend using a citation tool such as this one.

© Jul 8, 2026 OpenStax. Textbook content produced by OpenStax is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike License. The OpenStax name, OpenStax logo, OpenStax book covers, OpenStax CNX name, and OpenStax CNX logo, and Rice University name, and Rice University logo trademarks, or wordmarks are not subject to the Creative Commons license and may not be reproduced without the prior and express written consent of Rice University.