2.1 Cell Structure- Methods of study Flashcards
What are the three main types of microscope used to study cells?
Optical Microscope (light)
Scanning Electron Microscope
Transmission Electron Microscope
How much can you see through as optical microscope?
The nucleus, cell membrane and cytoplasm.
What are the advantages of an optical microscope?
They’re cheap, small and portable
They’re simple to prepare and use
A vacuum isn’t required
The natural colour of the sample is maintained
Living and dead material can be viewed
Unaffected by magnetic fields
What are the disadvantages of an optical microscope?
Lowest resolution
The magnification is only up to 2000
How do scanning electron microscopes work?
A beam of electrons are fired through the specimen (from above)
The electrons scatter depending on the contours of the specimen surface
A 3D image is produced by analysis of the pattern of scattered electrons
What are the advantages of scanning electron microscopes?
Election beam has short wavelength so the resolution is high
Electrons are negatively charged so the beam can be focused using magnets
They produce a 3D image
5000 times magnification
Sample can be any thickness
What are the disadvantages of scanning electron microscopes?
The specimens are killed
They’re more expensive
The image is in black and white
A vacuum is required
Preparation of the specimen can produce artefacts
Carries a small risk of radiation
Specimen must be conductive
How do transmission electron microscopes work?
A beam of electrons is focused onto the specimen (from below) by a condenser electromagnet
Some electrons are absorbed and others pass through
This produces an image than can my photographed to give a photomicrograph
What are the advantages of transmission electron microscopes?
Highest resolution
Highest magnification at 1 million times or more
Scientific, educational and industrial uses
Easy to operate with good training
Information gathered on surface features, shape, size and structure
What are the disadvantages of transmission electron microscopes?
Vacuum required Black and white image Samples are killed Samples must be thin Image may contain artefacts
What is the calculation for magnification?
Magnification=image size/size of real object
What is cell fractionation?
The process where cells are broken up and the different organelles they contain are separated out
Processes such as respiration and photosynthesis have been studied this way
Why is tissue cut up and kept in a cold, isotonic, buffered solution before cell fractionation?
Cold- reduces enzyme activity that might break down the organelle
Isotonic- prevent organelles bursting or shrinking as a result of osmosis
Buffered solution- keeps the pH the same so organelle structure is unchanged and enzyme function in unaffected
What is homogenation?
Blending of cells
Releases organelles from the cell by breaking down cell wall
Produces homogenate
This is filtered to remove any complete cells or large debris
How are organelles separated in cell fractionation?
The homogenised tissue is spun in an ultracentrifuge at low speed for 10 minutes to force the heaviest organelles to the bottom.
List the main components of a cell, heaviest to lightest?
Nuclei, mitochondria, lysosomes, endoplasmic reticulum, ribosomes.
What can be done to make a simple convex glass lens more effective?
Using them in pairs as in a compound light microscope
What do you call the material put under the microscope?
The object
What is the equivalent (in meters) of the following measurements? km m mm um nm
km- 10 ^3 m- 1 mm-10 ^-3 um- 10 ^-6 nm- 10 ^-9
Define resolution.
The minimum distance apart that two objects can be in order for them to appear as separate items
Higher resolution produces a clearer and more precise image
What does resolution depend on?
The wavelength or form of radiation used
What would a resolution of 0.2um mean?
Any objects that are 0.2um apart or more will be seen separately
Define ultracentrifugation.
The process by which the fragments in the filtered homogenate are separation in a centrifuge
It spins tubes of homogenate at high speeds to create a centrifugal force
The heaviest organelles move to the bottom
Describe the process of ultracentrifugation.
Filtrate spun slowly so heavy organelles (nuclei) form thin sediment at the bottom
Supernatant fluid is removed, transferred to a tube and spun at a higher speed to sediment the next heaviest organelle (mitochondria)
Why is a vacuum required for electron microscopes?
Electrons are absorbed or deflected by molecules in the air so a vacuum is needed for it to work effectively
What is an artefact?
Things that result from the way the specimen is prepared
Appear on photomicrograph but not part of the natural specimen
What is the significance of the sample for TEM being thin?
Allow electrons to penetrate
Produces 2D image
Multiple section can be taken to build up a 3D image
What is used to measure length directly through a microscope and how?
Eyepiece graticule
Calibrated for a particular objective lens with a stage micrometer
