Microscopy and Cell Structure

Microscopy in Cell Biology

• Microscopy has played a crucial role in the development of the cell theory and continues to aid scientists in understanding cell structure and function.
• Microscopes work by magnifying objects, with quality measured in terms of magnification and resolution.

Magnification and Resolution

• Magnification allows objects to appear larger.
• Resolution is the minimum distance between two points that can be distinguished as separate points.

Light Microscopes

• Light microscopes allow us to see cells and some of their contents, which cannot be seen with the naked eye.
• Light travels through the specimen, then through lenses to the eye or computer screen.
• The object appears magnified due to bending of light by lenses in the microscope.
• The light microscope can only resolve objects down to 0.2 micrometers in size.
• A micrometer (µm) is 1/1000th of a millimeter.

Types of Light Microscopes

• The compound light microscope is the most common type.
• Dissecting microscopes (stereo microscopes) are used to view whole organisms or the external structure of organisms.
• Dissecting microscopes have lower magnification and resolution than compound light microscopes.

Electron Microscopes

• Electron microscopes allow us to see cells and their contents with high magnification and greater resolution than light microscopes.
• The image from an electron microscope can be produced on a computer screen or photographic plate.
• Cells must be prepared for electron microscopy by being fixed, dehydrated, stained, and embedded in plastic resin.

Types of Electron Microscopes

• Transmission electron microscopes (TEM) require very thin specimens stained with heavy metals.
• TEM is used to show the internal structure of cells, known as "fine structure".
• Scanning electron microscopes (SEM) produce images of the surface features of cells and organisms.
• SEM uses a thin layer of gold metal atoms to create an image on a screen.