3.2.1.5 Studying Cells/Microscopy/Cell Fractionation (Unit 2 Cells) Flashcards
What you see when looking through a microscope is called the
Image
What is the biggest disadvantage of a light microscope?
- Low resolution due to ‘longer’ wavelength of light.
What are the advantages of a light microscope?
- True colour images but may sometimes require staining.
- Can observe live specimens
- Simple preparation of specimens
Define microscope resolving power.
The ability of a microscope to differentiate between 2 close together objects.
What is meant by magnification?
How much bigger an object looks under a microscope.
Magnification = Image Size ÷ Actual Size
What are the advantages of a transmission electron microscope (TEM)?
- High resolving power (0.1 nm)
- High magnification (X500, 000)
- Provides detailed images of internal structures of cells.
Name the 3 main microscopes used by scientists.
- Light microscope
- Scanning electron microscope (SEM)
- Transmission electron microscope (TEM)
What are the advantages of a scanning electron microscope?
- High resolution (20 nm)
- High magnification (X200, 000)
- 3D images of surface of the cells
Why do electron microscopes have a greater resolving power than light microscopes?
- They use electrons to interact with the specimen.
- Electrons have a shorter wavelength so interact more with the specimen.
What are the disadvantages of a transmission election microscope (TEM)?
- Special training is required before use.
- Samples must be dead as electrons are fired through a vacuum
- ‘Artefacts’ can be present in image from staining process.
- Sample must be 1 cell thick to allow electrons to penetrate specimen.
- Black and white images only so false colour must be used.
The resolving power of a light microscope is 2 µm what does this mean?
2 µm
It can differentiate between objects up to that distance apart.
What are the disadvantages of a scanning electron microscope (SEM)?
- Special training is required before use.
- Samples must be dead as electrons are fired through a vacuum and stains containing heavy elements are used.
- ‘Artefacts’ can be present in image from staining process.
- Black and white images only so false colour must be used.
- Cannot see inside specimens.
What are the main differences between scanning and transmission electron microscopes?
Does light or electons have the shortest wavelength?
Electrons
What is cell fracitonation?
The process by which cells are broken up and organelles are separated out.
Describe the stages of cell fractionation.
- Tissue is placed in a cold, buffered, isotonic solution.
- Tissue and cells are broken up using a homogeniser (blender)
- Homogenate is filtered to remove large debris.
- Nuclei in the homogenate are separated by being spun at low speed using a centrifuge (ultracentrifugation)
- Supernatent is removed leaving pellet of nuclei.
- Supernatent spun at medium speed to create pellet of mitochondrion/chloroplasts.
- Supernatent removed and spun at high speed to create pellet of ribosomes.
Before cell fractionation can take place, the tissue to be observed is placed in a cold, buffered, isotonic solution. Why is the solution cold?
To reduce enzyme activity within the cell that could break down organelles.
Before cell fractionation can take place, the tissue to be observed is placed in a cold, buffered, isotonic solution. Why is the solution isotonic?
If the solution was not of the same water potential as the tissue then organelles could burst as a result of osmotic gain or loss of water.
Identify what is missing from the unit conversion diagram.
What can we use to help rearrange the equations for calculating image size, actual size and magnification?
