Biyo-Tek Günlüğüm…

Microscopy

Measuring Cell Structures

Measurements taken by scientists are expressed in metric units. The official name of the metric system is the International System of Measurements, abbreviated SI. The table below summarizes the SI units used to measure length.

Two features of a microscope determine how clearly a small object can be viewed: magnification and resolving power.

Magnification is the ratio of the size of the image seen with the microscope to the actual size of the object.Resolution, or resolving power, is the capacity to distinguish fine detail in an image. This is defined as the minimum distance between two points at which they can both be seen separately rather than as a single, blurred point.There are four main types of microscopes that a biologist uses:

1. dissecting microscope
2. compound light microscope
3. Scanning Electron Microscope (SEM), and
4. Transmission Electron Microscope (TEM)

Dissecting Microscope: A dissecting microscope is often called a stereo microscope, or sometimes just referred to as a stereoscope.

Compound Light Microscope: used by most students, consists of a tube with glass lenses at each end. (Because it contains several lenses, the light microscope is sometimes called a compound microscope.) Visible light passes through the specimen being observed and through the lenses. Light is refracted (bent) by the lenses, magnifying the image.

Electron microscopes form an image of a specimen using a beam of electrons rather than light. The electron beam and specimen must be in a vacuum so that the electron beam will not bounce off of gas molecules. Live organisms cannot be viewed with an electron microscope.

Scanning Electron Microscope (SEM): the electron beam does not pass through the specimen. Instead, the specimen is coated with a thin film of gold or some other metal. The recorded emission patterns of the secondary electrons give a three-dimensional picture of the surface.