studying cells Flashcards
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 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) (higher than SEM)
- 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 higher resolution
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 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?
What is cell fracitonation?
The process by which cells are broken up by a homogeniser and organelles are separated out
Describe the stages of cell fractionation.
- Tissue is placed in a cold (decrease damage to enzyme), buffered, isotonic (prevent damage to organelles) 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.
Why is the solution cold?
To reduce enzyme activity within the cell that could break down organelles.
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.
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.
name 2 organelles foundin eukaryotes that cant be seen with a light microscope
mitochondria, ribosome, ER, cell surface membrane
when preparing a slide for viewing why must you press down hard on the coverslip (without breaking!)
for a single layer of cells to let light through
how do you prepare a temporary mount for viewing?
add drop of water to slide
take a thin section of tissue - 1 cell thick
place on glass slide (float on water)
add stain
place on coverslip
press down firmly
Contrast a TEM and a Optical microcope
TEM electrons - light optical
TEM greatER resolution
TEM can see smallER organelles e.g. ribosomes
TEM only dead specimens - light can view dead and live
TEM no colour - optical can
TEM needs thinnER specimen
If doing a scientific drawing at an image under the microscope what should you do to ensure the quality of it?
dont use shading
use SINGLE lines (no sketching)
add labels/annotations
dont cross label lines
add a magnification/scale bar
How caould you determine the mean length of a cell using an eye piece graticule?
calibrate the graticule using a ruler/stage micrometer
Measure the length of a number of cells (at random) using the graticule
calculate a mean
Identify what is missing from the unit conversion diagram.
