Biology Lesson # 1: The Microscope

Parts Since the invention of the microscope, scientists have been able to analyze the function and individual parts within animal and plant cells. The microscope that we are using is called a compound microscope, which uses light focussed through different lenses to form a magnified image of a specimen or object.

Magnification A simple microscope can have a magnification up to 20x (it could produce an image 20 times larger than the actual object). A compound microscope contains two magnification lenses (the objective and ocular lens), which when used together, allows for a larger magnification. For example, if the ocular lens is 10x magnification, and the highest objective lens is 40x magnification, then the total magnification is (10x) x (40x) = 400x magnification of the image!

Resolution We can magnify an image all we want, but if the original image details are unclear, we won’t be able to see much more when it is bigger. The resolution, or resolving power, is the ability to distinguish between two objects that are very close together.

Contrast Contrast is the difference in colour and light between the image and its background. Scientists often use stains to improve the contrast of the structures they are observing under the microscope. The most common stains are methylene blue and iodine. Sometimes scientists even use fluorescent dyes and then place the objects under ultraviolet (UV) light.

Electron Microscope An electron microscope uses a beam of electrons instead of light, and is much more powerful than a compound microscope. Some images can be magnified 1 500 000x! The downside to electron microscopes is that a beam of electrons can pass only through thin slices of a sample, so only thin cell samples can be studied, which means that living cells (which are thicker) cannot be studied, only ones that are dead.

Functions Body Tube - separates the ocular lens from the objective lens Revolving Nosepiece - holds and selects the objective lenses Objective Lenses - magnify specimen – 4x, 10x or 40x magnification are the most common Stage - supports the slide for observation

Functions (continued) Diaphragm - allows light to pass through the specimen Lamp - supplies the light that passes through the specimen Base - provides a stable platform for the microscope Fine Adjustment Knob - sharpens an image Coarse Adjustment Knob - moves the stage up or down to focus on the specimen

Functions (continued) Stage Clips - holds the slide in position on the stage Arm - holds the tube in place and is used to carry the microscope Ocular Lens (Eyepiece) - magnifies the specimen, usually by 10x magnification

Videos 25 Amazing Images with an Electron Microscope Parts of the Microscope Song