4. Microscopy

Light microscopes

Most student microscopes are classified as light microscopes. In a light microscope, visible light passes through the specimen (the biological sample you are looking at) and is bent through the lens system, allowing the user to see a magnified image. A benefit of light microscopy is that it can often be performed on living cells, so it’s possible to watch cells carrying out their normal behaviors (e.g., migrating or dividing) under the microscope.

A light microscope, of the sort commonly found in high school and undergraduate biology labs.

A light microscope, of the sort commonly found in high school and undergraduate biology labs.Image credit: OpenStax Biology. Modification of work by “GcG”/Wikimedia Commons.Student lab microscopes tend to be brightfield microscopes, meaning that visible light is passed through the sample and used to form an image directly, without any modifications. Slightly more sophisticated forms of light microscopy use optical tricks to enhance contrast, making details of cells and tissues easier to see.Another type of light microscopy is fluorescence microscopy, which is used to image samples that fluoresce (absorb one wavelength of light and emit another). Light of one wavelength is used to excite the fluorescent molecules, and the light of a different wavelength that they emit is collected and used to form a picture. In most cases, the part of a cell or tissue that we want to look at isn’t naturally fluorescent, and instead must be labeled with a fluorescent dye or tag before it goes on the microscope.The leaf picture at the start of the article was taken using a specialized kind of fluorescence microscopy called confocal microscopy. A confocal microscope uses a laser to excite a thin layer of the sample and collects only the emitted light coming from the target layer, producing a sharp image without interference from fluorescent molecules in the surrounding layers.

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