GCSE Biology (Combined) CCEA

Microscopy

Introduction to Microscopy

• Microscopes are instruments which magnify tiny details so they can be seen clearly.
• The study of objects under a microscope is called microscopy.
• A typical school microscope is a light microscope, using light to magnify the objects up to 2000 times their original size.
• The metric scale used in microscopy is the micrometre (µm) or nanometre (nm).

Types of Microscopes

• The light microscope, as used in school laboratories, is suitable for viewing cells and tissues.
• The electron microscope uses a beam of electrons instead of light to magnify objects up to two million times, allowing viruses and molecules to be seen.

Parts of a Microscope

• The eyepiece lens (or ocular lens) is where you look through, usually with a magnification of x10 or x15.
• The objective lenses sit above the specimen, with typically three or four with different magnifications (e.g., x4, x10, x40).
• The stage is where the slide with the specimen is placed.
• The focus knobs adjust the sharpness of the image, with coarse and fine focus adjustments.
• The light or mirror helps illuminate the specimen for better visibility.

Preparing a Slide

• To view a specimen under a microscope, it should be thinly sliced and mounted on a microscope slide.
• A staining agent such as iodine or methylene blue could be used to increase contrast and highlight different components of the cell.
• A cover slip should be gently eased down to avoid trapping air bubbles which can obstruct the view.

Understanding Magnification and Resolution

• Magnification is how much larger the image is compared to the actual size of the object, while resolution is the detail that can be seen.
• The formula to calculate magnification is Image size = Actual size x Magnification

Health and Safety Considerations

• Always carry a microscope with two hands - one under the base and one on the arm.
• Ensure slides are disposed of correctly to prevent injury.
• Glass slides can break easily and cause cuts, so handle them with care.

Understanding the Limits of Microscopy

• Although microscopes enable us to see small structures, they have their limitations.
• Light microscopes are limited by resolution; two objects closer than 200 nm appear as one.
• Electron microscopes may provide clear images of extremely small structures, but they can't be used to view living specimens.