Bio U1 - Methods of Studying Cells

What are the 3 types of microscope?

• Light / optical

• Transmission electron

• Scanning electron

What are the 4 principles of a light microscope?

1. Uses light to view specimen

2. Uses glass lenses to focus light

3. Specimen is held in water, oil etc. (may be stained)

4. Light passes through the specimen

What are the 3 principles for an electron microscope?

1. Uses a beam of electrons to view the specimen

2. Uses electromagnets to focus electrons

3. Specimen must be in a vacuum to allow electrons to travel

What are the principles of a transmission electron microscope (TEM)?

1. Electrons pass through the specimen

2. Denser parts of specimen absorb more electrons and so appear darker

3. Less dense parts absord less / fewer electrons so appear lighter

What are the principles of a scanning electron microscope (SEM)?

1. Electrons do not pass through the specimen but instea\d bounce off the surface

2. Electrons scatter due to contour of specimen and are collected by a detector to produce an image

What are 5 advantages to a light / optical microscope?

1. Images are in colour

2. Can view living specimens

3. Easier to use

4. Less preparation time

5. Cheaper

What are 4 advantages to electron microscopes?

1. Higher resolution due to shorter wavelength

2. SEM = 3D image

3. Higher magnification

4. Reveals the ultrastructure of cells (e.g. ribosomes)

What are 3 disadvantages to a light microscope?

1. Lower resolution due to longer wavelength of light

2. Lower magnification

3. Cannot see ultrastructure of cells

What are 6 disadvantages to electron microscopes?

1. More complex slide preparation

2. More difficult to use

3. Cannot view live specimens

4. Black and white images

5. TEM - 2D image only due to very thin specimen preparation

6. More expensive

What is an eyepiece graticule (EPG)?

A glass disc that is placed in the eyepiece lens of a microscope and used to measure objects

What is a stage micrometer?

A slide that is used to give the eyepiece gratitude real units (removed to measure cells)

What are the 2 stages to using an EPG?

1. Place EPG in the eyepiece lens

2. Calibrate EPG against a known scale to find units for measuring (for this, use a stage micrometer as the known scale)

What is magnification?

The number of times larger the image is compared to the actual object

What is image size?

The size (usually a length) of the object a measure on the magnified image

What is actual size?

The real size of the object (which has been magnified in the image)

What is the equation for magnification?

Magnifictaion = image size / actual size (“I AM” triangle)