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Microscopes

How can we see the details of bacteria?

With the naked eye, bacteria just look like a slimy smear on a petri dish. How can we study them in more detail? The invention of the microscope has allowed us to see bacteria, cells, and other things too small to be seen with the naked eye.

The Microscope

Microscopes, tools that you may get to use in your class, are some of the most important tools in biology ( Figure below ). A microscope is a tool used to make things that are too small to be seen by the human eye look bigger. Microscopy is the study of small objects using microscopes. Look at your fingertips. Before microscopes were invented in 1595, the smallest things you could see on yourself were the tiny lines in your skin. But what else is hidden in your skin?

Basic light microscopes opened up a new world to curious people.

Invention of the Microscope

Over four hundred years ago, two Dutch spectacle makers, Zaccharias Janssen and his son Hans, were experimenting with several lenses in a tube. They discovered that nearby objects appeared greatly enlarged, or magnified . This was the forerunner of the compound microscope and of the telescope. Later, the father of microscopy, Dutch scientist Antoine van Leeuwenhoek ( Figure below ) taught himself to make one of the first microscopes. In one of his early experiments, van Leeuwenhoek took a sample of scum from his own teeth and used his microscope to discover bacteria , the smallest living organism on the planet. Using microscopes, van Leeuwenhoek also discovered one-celled protists and sperm cells.

In 1665, Robert Hooke, an English natural scientist, used a microscope to zoom in on a piece of cork—the stuff that makes up the stoppers in wine bottles, which is made from tree bark. Inside of cork, he discovered tiny structures, which he called cells . It turns out that cells are the smallest structural unit of living organisms. This finding eventually led to the development of the theory that all living things are made up of cells. Without microscopes, this theory would not have been developed.

Antoine van Leeuwenhoek, a Dutch cloth merchant with a passion for microscopy.

Types of Microscopes

Some modern microscopes use light, as Hooke's and van Leeuwenhoek's did. Others may use electron beams or sound waves. Researchers now use these four types of microscopes:

  1. Light microscopes allow biologists to see small details of a specimen. Most of the microscopes used in schools and laboratories are light microscopes. Light microscopes use lenses, typically made of glass or plastic, to focus light either into the eye, a camera, or some other light detector. The most powerful light microscopes can make images up to 2,000 times larger.
  2. Transmission electron microscopes (TEM) focus a beam of electrons through an object and can make an image up to two million times bigger, with a very clear image.
  3. Scanning electron microscopes (SEM) ( Figure below ) allow scientists to find the shape and surface texture of extremely small objects, including a paperclip, a bedbug, or even an atom. These microscopes slide a beam of electrons across the surface of a specimen, producing detailed maps of the surface of objects.
  4. Scanning acoustic microscopes use sound waves to scan a specimen. These microscopes are useful in biology and medical research.

Scanning Electron Microscope (SEM) machine in cleanroom

A scanning electron microscope.

Vocabulary

  • bacteria : Microscopic one-celled prokaryotic organisms (without a nucleus).
  • cell : The basic unit of life.
  • light microscope : Tool that uses lenses to focus light in order to make things appear larger.
  • magnify : Making objects appear larger than they are.
  • microscope : Tool used to make things that are too small to be seen by the human eye look bigger.
  • microscopy : The technology for studying small objects using microscopes.
  • protist : Eukaryotic organism that belongs to the kingdom Protista; not a plant, animal, or fungi.
  • scanning acoustic microscope : Tool that uses sound waves to study a specimen too small to be seen with the naked eye.
  • scanning electron microscope (SEM) : Tool that sends a beam of electrons across the surface of a specimen, producing detailed maps of the shapes of objects.
  • transmission electron microscope (TEM) : Tool that focuses a beam of electrons through an object, magnifying it.

Summary

  • A microscope is a tool used to make things that are too small to be seen by the naked eye look bigger.
  • Types of microscopes include light microscopes, transmission electron microscopes (TEM), scanning electron microscopes (SEM), and scanning acoustic microscopes.

Practice

Use the resources below to answer the questions that follow.

  1. How should you carry a compound optical microscope?
  2. What procedure should you use when seeking to use the most powerful optical lenses?
  1. What light sources can you use with a dissecting microscope?
  2. Why is it important to have a fixed ocular lens and an adjustable ocular lens?
  3. What happens to your field of view as you increase magnification? Can you explain why this happens?
  1. How does an electron microscope differ from a light microscope? List all the differences you can think of.
  2. What kind of electron microscope is described in this video?
  3. How should you carry an electron microscope?
  1. How is the electron beam focused?
  2. What part of a specimen does a scanning electron microscope look at?
  3. Why is it important that a specimen for an electron microscope be placed in a vacuum? Why is this step unnecessary for a light microscope?

Review

  1. What is the purpose of a microscope?
  2. What were the findings of Hooke and van Leeuwenhoek?
  3. What are the differences between a light microscope and a scanning electron microscope?

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