Analysis of Cell Components Flashcards
Definition of magnification
The increase in apparent size of an object.
What is resolution/resolving power?
The ability to show two objects as separate (shows how detailed the image is, if a microscope can’t separate two objects then increasing the magnification will not help)
What is the equation for magnification?
I/AM - Image size = Magnification/Actual Size
What unit do you always convert to?
Millimetres - mm
What do you multiply by to convert between units?
Metre (m) x1000 Millimetre (mm) x1000 Micrometre (um) x1000 Nanometer (nm)
nm /1000 um /1000 nm /1000 m
How would you draw a cell under a microscope?
Draw the cell within a circle, label each organelle and their function, add the magnification, label the cell type.
What can you presume when looking at a magnified image of a cell.
The outer layer of the cell is the cell wall (depending on context - cell type), the eye piece is x10 magnification (times 10 by the magnification of the lenses), if you don’t know what an organelle is then ignore it.
How would you measure the size of a cell from looking down a microscope?
Measure the field of view (diameter, circle) with a mm ruler by putting it directly on top of the specimen, count the number of cells and divide by this number, (calculate using I/AM?)
How do scale bars work?
The length of the bar is the image size and the size the bar represents is the actual size.
What dp/sgf do you leave your answer to?
Usually 3sgf but the same amount as in the question.
Name the two types of microscope.
Optical (light) microscope, Electron Microscope (can be a Transmition Electron Microscope or a Scanning Electron Microscope).
Differences in illumination between an Optical microscope, SEM’s and TEM’s?
Optical - Light, SEM + TEM - Electron beam
Difference in what focuses the image in an Optical microscope, SEM’s and TEM’s?
Optical - Objective lenses, SEM + TEM - Condenser Electromagnets
Differences in max magnification between an Optical microscope, SEM’s and TEM’s?
Optical - x1500, SEM - 500, 000 (or 1-2 mill), TEM - x50mill
Differences in resolving power between an Optical microscope, SEM’s and TEM’s?
Optical - 200nm (worst), TEM - 1nm (best), SEM - 20nm (middle)
Differences in specimens between an Optical microscope, SEM’s and TEM’s?
Optical - Living or Dead, SEM + TEM - Dead (specimens have to be placed in a chamber under vacuum so electrons aren’t absorbed by the air)
Differences in specimen thickness between an Optical microscope, SEM’s and TEM’s?
Optical - thin, TEM - Extremily thin to allow electrons to penetrate, SEM - thicker than TEM (and optical - can view whole cells/tissues)
Differences in ease of preparation between an Optical microscope, SEM’s and TEM’s?
Optical - Easiest, SEM - next easiest, TEM - slightly harder than SEM
Differences in cost of equipment between an Optical microscope, SEM’s and TEM’s?
Optical - Cheaper, TEM + SEM - More expensive
Differences in image colour between an Optical microscope, SEM’s and TEM’s?
Optical - Colour, TEM +SEM - Black and white but can be coloured using a computer
Differences in image dimension between an Optical microscope, SEM’s and TEM’s?
Optical + TEM - 2D, SEM - 3D
Disadvantages and advantages of a light (optical microscope)?
Poor resolution - light has a longer wavelength than electron beam.
Lower Magnification
However - Colour images
Can view LIVING samples
How is the image produced on a light microscope?
A beam of light is condensed to produce the image.
How does a transition electron microscope work?
Condenser electromagnets are used to focus a beam of electrons, which is then transmitted through a small section of the specimen. Denser parts of the specimen absorb more electrons which makes them look darker, lighter parts allow electrons to pass through making it look brighter.
What can you see when looking through a transition electron microscope?
A 2D slice of the specimen, you can see ribosomes and the internal structures of larger organelles like chloroplasts because of its high resolution.
What is the image produced from a transition electron microscope called?
The 2D image produced (a MICROGRAPH) can be photographed to produce an electronmicrograph/photomicrograph
How does a scanning electron microscope work?
A beam of electrons from above is focused by condenser electromagnets and then passed through pairs of scanning coils which deflect the beam horizontally and vertically across a portion of the specimen in a regular pattern resulting in scattering of electrons and emission of secondary electrons from the surface of the specimen which are gathered in a cathode ray tube to produce an image. The pattern of scattering depends on the contours of the specimen’s surface which creates the 3D image.
What do the images produced by a scanning electron microscope show?
The surface of the specimen (are 3D), images a larger area of the specimen, images are often easier to interpret than TEM images
What are the disadvantages of electron microscopes?
Vacuum used so only dead specimens can be used.
Complex preparation and scanning of specimens required.
Image only in black and white.
Image (photomicrograph) may contain artefacts which result from the way the specimen’s are prepared eg. dehydration of a specimen may result in distortion of key features.
Advantages of an electron microscope?
Higher magnification and resolving power.
When is a temporary mount used?
Also known as a wet mount, used to prepare a specimen when you want to look at it through a light microscope.
What is the process to make a temporary/wet mount?
Pipette a drop of liquid (eg. water/oil) onto the centre of the slide.
Use tweezers to place a thin (needs to let light through so can’t be thick) slice of the specimen on top of the water droplet.
Add a drop of stain.
Add the cover slip (a square piece of glass that protects the specimen) by tilting and lowering it so it covers the specimen.
What are stains used for when preparing a specimen to go under the microscope?
To highlight objects in a cell. (eg. eosin is used to make the cytoplasm show up and iodine in potassium iodide solution is used to stain starch grains in plant cell.
What must you be careful not to do when preparing a slide for a light microscope?
Not get any air bubbles as they obstruct the view of the specimen.
What are artefacts?
The things you can see down a microscope that aren’t part of the cell or specimen you are looking at.
Examples of artefacts?
Dust, air bubbles, finger prints, inaccuracies caused by squashing and staining your sample.
Where are artefacts especially common?
Electron microscopes because slides need a lot of preparation.
How did the first scientists distinguish between artefacts and organelles?
By repeatedly preparing specimens in different ways. If it showed up on one but not another it was an artefact.
