Topic 7 Microscopy
“Micro” refers to tiny, “scope” refers to view or look at. Microscopes are tools used to enlarge images of small objects so as they can be studied. The compound light microscope is an instrument containing two lenses, which magnifies, and a variety of knobs to resolve (focus) the picture. Because it uses more than one lens, it is sometimes called the compound microscope in addition to being referred to as being a light microscope.
Describe the relative sizes of different kinds of cells
- Describe: Give a detailed account or picture of a situation, event, pattern or process.
Biology is a visually rich subject area. However, many of the most interesting biological events and structures are smaller than the unaided human eye can see. In fact, human eyes have a resolution of about 100 µm. On the chart below, notice that of all the structures listed, only the plant cell is within our resolution--just barely.
Relative Sizes of Biological Materials
- Eukaryotic cell (plant) = ~100 μm
- Eukaryotic cell (animal) = ~10 – 50 μm
- Organelle (e.g. mitochondrion) = ~1 – 10 μm
- Prokaryotic cell (bacteria) = ~1 – 5 μm
- Virus = ~100 nm
- Plasma membrane = ~7.5 nm
- Molecules (e.g. glucose) = ~1 nm
- Atoms = ~100 pm
Compare and contrast light and electron microscopes
- Compare and Contrast: Give an account of the similarities and differences between two (or more) items or situations, referring to both (all) of them throughout.
The smallest objects that the unaided human eye can see are about 0.1 mm long. That means that under the right conditions, you might be able to see an amoeba proteus, a human egg, and a paramecium without using magnification. A magnifying glass can help you to see them more clearly, but they will still look tiny.
Smaller cells are easily visible under a light microscope. It's even possible to make out structures within the cell, such as the nucleus, mitochondria and chloroplasts. Light microscopes use a system of lenses to magnify an image. The power of a light microscope is limited by the wavelength of visible light, which is about 500 nm. The most powerful light microscopes can resolve bacteria but not viruses.
To see anything smaller than 500 nm, you will need an electron microscope. Electron microscopes shoot a high-voltage beam of electrons onto or through an object, which deflects and absorbs some of the electrons. Resolution is still limited by the wavelength of the electron beam, but this wavelength is much smaller than that of visible light. The most powerful electron microscopes can resolve molecules and even individual atoms
There are two main types of microscope: optical (light) microscopes and electron microscopes
Light Microscopes
Electron Microscopes
Living specimens can be viewed in their natural color using light microscopes, although stains are usually applied to enhance specific structures
Smaller cells are easily visible under a light microscope. It's even possible to make out structures within the cell, such as the nucleus, mitochondria and chloroplasts. Light microscopes use a system of lenses to magnify an image. The power of a light microscope is limited by the wavelength of visible light, which is about 500 nm. The most powerful light microscopes can resolve bacteria but not viruses.
To see anything smaller than 500 nm, you will need an electron microscope. Electron microscopes shoot a high-voltage beam of electrons onto or through an object, which deflects and absorbs some of the electrons. Resolution is still limited by the wavelength of the electron beam, but this wavelength is much smaller than that of visible light. The most powerful electron microscopes can resolve molecules and even individual atoms
There are two main types of microscope: optical (light) microscopes and electron microscopes
Light Microscopes
- Use lenses to bend light and magnify images by a factor of roughly 100-fold
- Can be used to view living specimens in natural color
- Chemical dyes and fluorescent labeling may be applied to resolve specific structures
Electron Microscopes
- Use electromagnets to focus electrons resulting in significantly greater magnifications and resolutions
- Can be used to view dead specimens in monochrome (although false color rendering may be applied)
- Transmission electron microscopes (TEM) pass electrons through specimen to generate a cross-section
- Scanning electron microscopes (SEM) scatter electrons over a surface to differentiate depth and map in 3D
Living specimens can be viewed in their natural color using light microscopes, although stains are usually applied to enhance specific structures
image from bioninja.com
Demonstrate the proper procedures used in correctly using the compound light microscope
- Demonstrate: Make clear by reasoning or evidence, illustrating with examples or practical application
A microscope is a high quality instrument and should last 25-30 years if treated properly and with care. Following these simple instructions will not only help you care for your microscope and keep it in good working condition, but will also help you get the most out of your microscope.
When attempting to draw microscopic structures, the following conventions should be followed:
When attempting to draw microscopic structures, the following conventions should be followed:
- A title should be included to identify the specimen (e.g. name of organism, tissue or cell)
- A magnification or scale should be included to indicate relative size
- Identifiable structures should be clearly labelled (drawings should only reflect what is seen, not idealised versions)
Draw cell structures as seen with the light microscope.
- Draw: .Represent by means of a labelled, accurate diagram or graph, using a pencil. A ruler (straight edge) should be used for straight lines. Diagrams should be drawn to scale. Graphs should have points correctly plotted (if appropriate) and joined in a straight line or smooth curve.
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Calculation of the magnification of drawings and the actual size of structures and ultrastructures shown in drawings or micrographs.
Cells and their components are measured according to the metric system.
To calculate the linear magnification of a drawing or image, the following equation should be used:
Magnification = Image size (with ruler) ÷ Actual size (according to scale bar)
Calculation of Actual Size:
To calculate the actual size of a magnified specimen, the equation is simply rearranged:
Actual Size = Image size (with ruler) ÷ Magnification
Calculation of Actual Size:
To calculate the actual size of a magnified specimen, the equation is simply rearranged:
Actual Size = Image size (with ruler) ÷ Magnification
Key Terms:
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centimeter
electron microscope eyepiece light microscope |
magnification meter
micrograph micrometer |
microscope
millimeter nanometer objective lens |
resolution
STEM TEM stage |
prepared slide
light source wet slide cover slip |
Class Material:
Correct use of terminology is a key skill in Biology. It is essential to use key terms correctly when communicating your understanding, particularly in assessments. Use the quizlet flashcards or other tools such as learn, scatter, space race, speller and test to help you master the vocabulary.
Useful Links:
Amazing Cells resource from Learn.Genetics at Utah
BioVisions: Modifying Cell Identity through Reprogramming
The Big and the Small
Sense of scale
University of Utah Cell Size and Scale
PLOS Biology: How Are The size of Cells, Organs and Bodys Controlled
Amazing Cells resource from Learn.Genetics at Utah
BioVisions: Modifying Cell Identity through Reprogramming
The Big and the Small
Sense of scale
University of Utah Cell Size and Scale
PLOS Biology: How Are The size of Cells, Organs and Bodys Controlled
Video Clips
Explore how to use a light microscope with the Amoeba Sisters! Includes microscope parts, how to use, and some helpful tips! Additionally, this video introduces a few types of light microscopes as well as electron microscopes
Humans have long known that glass bends light. However, it took us awhile to figure out that stacking lenses in a tube would open up a whole new world to science, finally allowing us a peek at the microscopic.
In recent years, scientists have come up with new ways to hack the physics of light, to invent the most powerful microscopes the world has ever seen.
Tutorial describing the differences between three key microscopes; the light, scanning electron and transmission electron microscope
How to Use a Microscope with Murry Gans.
Learn the parts of the microscope and how to focus a compound microscope. Using a compound microscope can be fun and unlocks a whole new world.
