CHAPTER 6 SECTION 6.1

By: C.J. Williams and Cirstyn Michel

The Light Microscope• In the 1600’s the light

microscope (LM) was invented.

• A light microscope passes visible light through the specimen and glass lenses. The light is bent by the lenses magnifying the specimen.

• The light microscope cannot resolve specimen smaller than 2 micrometers, so objects being seen using a LM are limited.

Onion Skin under a light microscope

Electron Microscope

Electron microscopes (EM) are much clearer and stronger than a light microscope.

It works by focusing a beam of electrons onto the specimen.

Electron Microscopes allow you to see the finer details such as cell organelles and even molecules and atoms.

There are two types of EM: Scanning Electron Microscopes and Transmission Electron microscopes

Scanning Electron Microscope (SEM): SEM’s are used for more detailed images of an imaging surface. It shows an almost 3D image of a specimens topography

Transmission Electron Microscope (TEM): TEM’s are used to study the internal structure of a cell. Allows you to see organelles in a cell.

Parameters of Microscopy

Magnification: ratio of an objects image size to its actual size

Resolution: Measure of clarity of the image

Contrast: accentuates different parts of a sample

Summary of Key Concepts

Improvements in microscopy that effect the parameters of magnification, resolution, and contrast have catalyzed progress in the study of cell structure.

Light microscopy and electron microscopy remain important tools.

Cell Fractionation

Vocabulary: Cell Fractionation- the disruption of a cell

and separation of its organelles by centrifugation (rotation used to separate substances of different densities).

Cell Fractionation

Cell fractionation takes cells apart and separates the major organelles and other subcellular structures from one another.

The instrument used is the centrifuge, which spins test tubes holding mixtures of disrupted cells at various speeds. Those forces cause a fraction of the cell components to settle at the bottom of the tube, creating a pellet. At lower speeds, the pellet will consist of larger components, and the opposite for higher speeds.

Cell Fractionation

Enables researchers to prepare specific cell components in bulk and identify their functions.

Cell Fractionation

Method Example:

Cell Fractionation

Summary:Cell biologists can obtain pellets

enriched in particular cellular components by centrifuging disrupted cells at sequential speeds. Larger components are in the pellet after lower speed centrifugation, and smaller components after higher speed centrifugation.

Concept Check 6.1

1. How do stains used for light microscopy compare with those used for electron microscopy?

2. Which type of microscopy would you use to study (a) the changes in shape of a living white blood cell, (b) the details of surface texture of a hair, and (c) the detailed structure of an organelle?

Concept Check 6.1 Answers

1. Stains used for light microscopy are colored molecules that bind to cell components, affecting the light passing through, while stains used for electron microscopy involve heavy metals that affect the beams of electrons passing through.

2. (a) Light microscope, (b) scanning electron microscope, (c) transmission electron microscope.