1 of 6© boardworks ltd 2009. 2 of 6© boardworks ltd 2009 getting some perspective the study of...

1 of 6 © Boardworks Ltd 2009


Getting some Perspective

• The study of Biology involves the study of a lot of things that can’t be seen without the aid of a microscope.

• Activity 1: http://learn.genetics.utah.edu/content/begin/cells/scale/

• Determine what you think the correct order of the items is: Biggest (1) to Smallest (9).


Solution for Coffee to Carbon

• coffee bean• grain of salt• amoeba• paramecium• human egg cell• skin cell• red blood cell• sperm cell• baker's yeast

• mitochondria• E. coli bacteria• Influenza virus• ribosome• antibody• hemoglobin• phospholipid• glucose• adenine• carbon atom


So Small, We Need New Units of Measure

As you saw in the Coffee to Carbon activity, the incredibly small size of some objects requires the use of units that are much smaller than those previously used.

millimeters mm 10 millimeters = 1 centimeter

micrometers µm 1000 micrometers = 1 millimeter

nanometers nm 1000 nanometers = 1 micrometer

picometers pm 1000 picometers = 1 nanometer

What is the smallest unit you think you can see with your unaided eye?


How small is a cell?


Light microscopes

Light (or optical) microscopes use lenses to project a magnified image of an object onto the eye.

Light microscopes are limited to a magnification of 1500× by their resolving power (resolution). This is a measure of their ability to distinguish between two separate points. A light microscope cannot resolve two points that are closer than half a wavelength of visible light (250 nm).

Magnification is a measure of how many times bigger the image is than the object:

size of image

actual size of the objectmagnification =


Electron microscopes


Two views of the Ebola virus

http://connect.in.com/ebola/photos-ebolavirusundermicroscope-1190603392496.html


Preparing a specimen for microscopy

Electron microscopes contain a vacuum, as air particles would interfere with the beam of electrons.

Optical microscopes can be used to view living specimens. Colored dyes (stains) can be used to make specific structures more visible under a light microscope.

Water boils at room temperature in a vacuum, so the specimen must be dried out completely (dead).


More about Light Microscopes

• Optical, or light, microscopes are what you’ll be using in class to observe cells.


Microscope characteristics


Proper Use of the Microscope: Important!

ALWAYS carry a microscope with 2 hands. One under the base and one holding the arm of the microscope.


Proper set-up and use of the microscope

1. Orient the microscope so the stage is facing you, not the microscope arm.

Turn/twist the eyepiece around so it is angled toward you.

The focus knobs will be at the back.

2. Turn on the light.

3. Rotate the nosepiece to put the scanning power objective lens in place, centered over the hole in the stage.

The shortest lens; the lowest magnification power.

Total magnification = eyepiece lens x objective lens


4. Place the glass slide on the stage, center the specimen.

Visually place the “specimen” on the slide over the small circle on the stage where light shines through.

5. Look through the eyepiece. Use the coarse adjustment knob to move the stage and bring the “specimen” into focus.

The diaphragm under the stage adjusts the amount of light coming through.


6. Turn the nosepiece to center the low power objective over the slide. It must “click” into place.

7. Use the fine focus adjustment knob to bring the specimen into focus.

If directed to go to high power, only use the fine focus adjustment!

If the specimen goes out of focus, back up to low power or even scanning power and start again.


Making a “wet mount”

1-2 drops of water or stain put over the specimen.

Put coverslip down at a 45° angle and slowly lay it down.

Wick away any excess liquid.

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