3.2.1.3 Studying cells Flashcards
What is magnification?
How many times bigger an object appears
What is resolution?
Ability to distinguish two points (how close together two points can be and still be seen as separate points)
How do you calculate magnification from a scale bar or image?
Magnification = (image size)/(actual object size)
How do you calculate actual size from an image of known magnification?
Actual object size = (image size)/magnification
What is the conversion of 1000µm in 1mm?
1000µm = 1mm
What is the conversion of 1000nm in 1µm?
1000nm = 1µm
What is the first step in measuring an object using a microscope and graticule?
Line up the graticule with the object
What do you do after counting the number of eyepiece units for the measurement?
Multiply the number of eyepiece units by the calibration factor
What is the purpose of calibrating the graticule using a stage micrometer?
To determine how many µm per eyepiece unit
What is the resolution of optical (light) microscopes?
0.2µm
What is the magnification range of optical (light) microscopes?
x2000 - x1500
How do optical (light) microscopes work?
Light waves are focussed onto an object, and then onto the eye, using glass lenses
What are some uses of optical (light) microscopes?
Study living and dead cells; cells can be stained to see features more easily
What are the limitations of optical (light) microscopes?
Relatively low magnification and resolution, cannot see all organelles in a cell
What is the resolution of a transmission electron microscope (TEM)?
0.1nm
What is the magnification of a transmission electron microscope (TEM)?
x50 000 000
How does a transmission electron microscope (TEM) work?
Beams of negatively charged electrons are focused using electromagnets and pass through the cell
What are the uses of a transmission electron microscope (TEM)?
View ultrastructure of cells (all organelles can be visualised)
What are some limitations of a transmission electron microscope (TEM)?
- Vacuum required for microscope to function
- Specimen must be very thin
- Staining with metals required
- Cells must be dead
- Artefacts may occur
What is the resolution of a scanning electron microscope (SEM)?
20nm
What is the magnification of a scanning electron microscope (SEM)?
x1 000 000
How does a scanning electron microscope (SEM) work?
Beams of negatively charged electrons are focused using electromagnets and reflect off the surface of an object
What are the uses of a scanning electron microscope (SEM)?
Beam is scanned across the surface, allowing a 3-D image to be built up
What are some limitations of a scanning electron microscope (SEM)?
- Vacuum required for microscope to function
- Specimen must be very thin
- Staining with metals required
- Cells must be dead
- Artefacts may occur
