GCSE Biology (Triple) CCEA

Microscopy

Microscopy and Cell Observation

Overview of Microscopy

• Microscopy is the science of using a microscope to view objects that are too small to be seen with the naked eye.
• The first microscope was invented in the late 16th century by Zacharias Jansen.
• Modern microscopes can magnify objects up to 1,000 times their original size, which allows us to study cell structures in detail.

Types of Microscopes

• The light microscope uses light to illuminate the specimen. It can magnify up to 1,500 times.
• The electron microscope uses a beam of electrons instead of light. It can magnify up to two million times.
• Electron microscopes are much more powerful but also a lot more expensive. They are usually found in professional laboratories.

Microscope Components

• The eyepiece or ocular lens is where you look into the microscope. It usually has a magnification of x10.
• The objective lens collects light from the sample. There are usually several on a rotating disk, each with a different magnification.
• The stage holds the slide. It can be moved up and down to bring the specimen into focus.
• The condenser lens focuses the light on the specimen.
• The light source illuminates the specimen.
• The coarse and fine adjustment knobs modify the focus.

Preparing Slides for Observation

• Stains or dyes are often used to help to see certain parts of cells more clearly.
• Hydrophilic stains, such as iodine or methylene blue, are water-soluble and bind to water-containing tissues.
• Hydrophobic stains, such as Sudan stains, bind to nonaqueous cells components like fat.
• Always take appropriate care when handling stains as they can be toxic and a hazard to the skin and eyes.

Using Microscopes

• When adapting to a new magnification, use the coarse adjustment knob first to bring the sample into view.
• Then use the fine adjustment knob to get a clear view.
• Always start at the lowest magnification and work up to higher powers.
• Remember to adjust the light intensity and contrast when the magnification is changed.
• Store microscopes properly to avoid damage and dust accumulation. Always cover the microscope when not in use.

Electron Microscope vs. Light Microscope

• Electron microscopes allow us to view objects far smaller than those viewable with a light microscope, such as viruses and the ultrastructure of cells.
• They provide high resolution images due to short wavelength of electrons.
• However, they're very expensive to buy and use, demand high voltage, and samples have to be treated before they can be viewed.
• In contrast, light microscopes are far more readily available and easy to use, and are suitable for viewing live organisms.
• They are less powerful, but they can be used in a normal laboratory or classroom, and can be used to observe phenomena such as cell division in real-time.