What you see when looking through a microscope is called the
Image
What are the disadvantages of a light microscope?
- Low resolution due to ‘longer’ wavelength of light.
- Low magnification (X1,250 max)
- Thin specimens may not represent true specimen.
What are the advantages of a light microscope?
- Easy to use (no special training required)
- Cheap (
- True colour images but may sometimes require staining.
- Can observe live specimens
Define microscope resolving power.
The ability of a microscope to differentiate between 2 close together objects.
What is another term for resolution?
Resolving power
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
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 witht he 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 and stains containing heavy elements are used.
- ‘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.
- 2D images - 3D possible but complicated and slower than SEM.
- High cost
- High energy electron beams can destroy the specimen.
What is the resolving power of a light microscope and 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.
- High cost
- High energy electron beams can destroy the specimen.
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 cell 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.
- 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.
Before cell fractionation can take place, the tissue to be observed is placed in a cold, buffered, isotonic solution. Why is the solution buffered?
So that pH is maintained.
A change in pH could affect the enzymes within the cells.
A change in pH could affect the structure of organelles within the cells.
What is a homogeniser?
A blender used to break up tissues and cells and release organelles.
What is a homogenate?
The resulting fluid after homogenisation
What is a centrifuge?
A machine that spins tubes of homogenate at varying speeds (used in cell fractionation)
name 2 organelles foundin eukaryotes that cant be seen with a light microscope
mitochondria, ribosome, ER, cell surface membrane
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3.1.2.1 Introduction to Biological Molecules39
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3.1.2.2 Carbohydrates - Monosaccharides to Polysaccharides48
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3.1.2.3 Reducing and Non-Reducing Sugar Tests20
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3.1.2.4 Polysaccharides structure and function and the starch test35
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3.1.3 Lipids - Triglycerides, Phospholipids and the Emulsion Test40
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3.1.4.1 Proteins - structure, function and biuret test47
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3.1.4.2 Proteins - Enzyme Action25
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3.1.4.3 Proteins - Factors Affecting Enzyme Action20
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3.3.3.1 Proteins - Enzymes and Digestion55
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3.3.3.2 Absorption of the Products of Digestion42
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3.1.5.1 Structure of DNA and RNA43
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3.1.5.2 DNA Replication18
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3.1.6 Energy and ATP30
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3.2.1.1 Eukaryotic Cell Structure87
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3.2.1.2 Organelle Structure and Function39
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3.2.1.3 - Specialised Cells43
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3.2.1.4 - Structure of Prokaryotic Cells48
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3.2.1.5 - Light and Electron Microscopes32
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3.2.1.6 - Cell Calculations and AIM Triangle18
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3.2.2 - Mitosis and Cell Cycle37
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3.2.3.1 - Cell Membrane Structure and Function30
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3.2.3.2 - Simple and Facilitated Diffusion23
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3.2.3.3 - Osmosis17
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3.2.3.4 - Active Transport15
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3.2.4.1 - Cell Recognition22
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3.2.4.2 - Phagocytosis9
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3.2.4.3 - Cell Mediated Immunity12
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3.2.4.4 - Humoral Immunity10
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3.2.4.5 - Monoclonal Antibodies21
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3.2.4.6 - Vaccination15
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3.2.4.7 - HIV21
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3.3.1 Surface area to volume ratio22
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3.3.2 Gas Exchange36
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3.3.4.1 Mass Transport in animals33
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3.3.4.2 Mass Transport in plants23
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3.4.1.1 DNA, genes and chromosomes25
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3.4.2 DNA and protein synthesis36
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3.4.3 Genetic Diversity - mutations and meiosis27
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3.4.4 Genetic diversity and adaptation28
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3.4.5 Species and taxonomy34
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3.4.6 Biodiversity within a community19
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3.4.7 Investigating diversity29
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3.1.7 and 8 water and other ions7
