Microscopes

MICROSCOPES

–  Magnification: –  Resolution: –  Field of View: Describes the visual picture seen when

looking through the eyepiece of the microscope

7X 45X 112.5X 225X

Van Leeuwenhoek •  In the 17th century, amateur

scientist Anton Leeuwenhoek enlightened the world about what he dubbed “animacules” such as protozoa found in standing water.

•  Using microscopes he made himself, Leeuwenhoek wrote up what he viewed in pond water, plant material, even gunk scraped off his teeth.

•  He was the first to identify sperm and red blood cells.

1st crude microscope made by the Dutchman

Leeuwenhoek’s Microscope

2 MainTypes of Microscopes

Light Electron

Scanning Transmission Scanning-Tunneling Stereomicroscope Compound

COMPOUND LIGHT MICROSCOPES

•  Can magnify up to 1,000x •  Powerful enough to view

algae, protozoa •  Some powerful enough to

view bacteria •  CANNOT view tiny parts

of cells (organelles) or view viruses in detail

•  Sample must be larger than 0.2mm

•  Samples must be stained •  2D image of dead or alive

Compound Light Microscope

Paramecium 25x mag.

Diatom

Euglena 400x mag.

Compound Microscope Images

UD Virtual Compound Microscope

STEREOMICROSCOPE •  Also called a

dissecting microscope •  Magnifies 10X •  Reserved for larger

objects that can be seen with your eyes but may need magnification for details

•  Image is 3D

Stereomicroscope

Moth pupa

Details of a spider’s foot

Details of a fly tongue

Detail of concrete sample

Electron Microscopes •  Developed in the 1940’s •  View extremely tiny objects (organelles,

viruses) •  Use streams of electrons instead of light to

create images •  No living samples •  Scientists don’t see the images directly

through lenses as they do with light microscopes. Instead, the machinery of the electron microscope generates a picture on a TV or computer screen.

SEM Scanning Electron Microscope

•  The specimen is usually coated with an ultra-thin layer of heavy metals/gold.

•  The electron beam scans over the surface of the specimen, exciting electrons on the surface.

•  Especially useful for studying the surfaces and structures of cells

•  First commercial SEM was built in 1965

•  Scanning EM –  3D image –  Specimens not sliced for

viewing –  100,000X magnification –  Cannot be used to view living

specimens

Daisy Petal

•  Bread mold (1200x) •  Penicillium is the stuff

the antibiotic is made from and grows not only on bread but on citrus fruits as well.

Virtual Scanning Electron Microscope

•  Start here!

TEM Transmission Electron Microscope

•  Transmit electron beams through a thin section or slice of a specimen to create an image.

•  TEMs are particularly useful for studying the insides of cells.

•  Cannot be used to study living cells

•  2D image with 200,000X magnification

•  First built in 1931

TEM

Mitochondria

Microtubules Cardiac muscle

STM Scanning-Tunneling Microscope

•  Display things as minute as the individual atoms on an object’s surface. 100 million X

•  They use an electrically charged tip that is placed within nm of the surface of the specimen. Electrons “jump” between the tip and the specimen surface in what’s called the tunneling current.

•  As the tip is moved back and forth across the specimen, the current varies according to whether the tip is right over an atom or over the space or trough between atoms.

•  A computer creates an image based on these differences in current.

The STM can even move atoms about. The image below depicts the results of such a

process.

Xenon atoms on a nickel substrate

spell IBM

A scanning tunneling microscope image of 5 nm gold nanoparticles

Nano- means 1/1,000,000,000th

Atomic Force Microscope

•  IBM article 8/28

Light Microscopes (compound)

•  Specimen mounted on a glass slide on stage

•  Must be thinly sliced or very small

•  Pair of lenses – Ocular lens (eye

piece) – 10X – Objective lens (nose

piece)

•  Magnification determined by multiplying power of the objective & ocular lenses

•  Maximum magnification is around 2000X for the best microscopes

Different parts of a microscope

Magnification

•  Magnification is represented by a whole number that is sometimes followed by an “x”

Record the following in your lab notebook: •  Magnification of eyepiece? •  Magnification of scanning objective? •  Magnification of low power objective? •  Magnification of high power objective?

Total magnification

•  To calculate the total magnification, multiply the magnification of the eyepiece times the magnification of the objective to calculate total magnification

Record the following in your lab notebook: •  Total magnification under scanning? •  Total magnification under low power? •  Total magnification under high power?

Drawing specimens

•  Always use pencil so you can erase and shade

•  Draw a circle first which represents your field of view (the area you can see while looking through your microscope)

•  Draw your specimen to scale (how big is it compared to your field of view)

•  Label each drawing with the name of the specimen and the total magnification

Focusing a Microscope

•  On low power, use the Coarse adjustment knob to focus

•  On high power, use the fine adjustment knob to focus

5 grains of salt •  Using the rules for drawing a specimen,

draw a grain of salt under scanning, low, and high power

•  Create your slide, by slightly wetting your fingertip and gently rubbing the slide with it. Now sprinkle five grains of salt on the moisture. Record your observations/sketches in your lab notebook.

Making a wet mount slide Procedure •  Place a drop of water on the center of a clean dry slide •  Place the specimen in the middle of the drop. •  While holding the cover slip upright, carefully place one edge of

the cover slip next to the water. •  Slowly lower the upper edge of the cover slip onto the water. The

objective is to minimize or eliminate air bubbles under the cover slip. You might find it helpful to use one toothpick to hold the lower edge in place, while using another to carefully lower the slip into place.

Questions for Thought •  Why would you want to wet mount a specimen? (To increase its

translucency and to make it easier to stain. It also has a tendency to flatten the subject, making it easier to view.)

Common Metric Prefixes used in Biology

•  Kilo- means 1000 •  Centi- means 1/100th

•  Milli- means 1/1000th

•  Micro – means 1/1,000,000th

•  Nano- means 1/1,000,000,000th

Cell sizes

Cell Size Interactive Site

How Big is a ... ?