2.1.4 Magnification And Resolution Flashcards
Magnification Formula
Image Size = actual size * magnification
The size of cells is typically measured using micrometers, with sub cellular structures measured in micrometers or nanometers
When doing calculations, all measurements must be in the same units
- it is best to use the smallest unit of measurement shown in the question
Magnification does not have units
Converting Units of Measurement
There are 1000 nanometers is a micrometer
There are 1000 micrometers in a millimetre
There are 1000 millimetres in a metre
Magnification
Magnification is how many times bigger the image of a specimen observed is compared to the actual size of the specimen
A light microscope has two types of lenses:
- an eyepiece lens, that typically has a magnification of x10
- a series of (usually 3) objective lenses, each with a different magnification
To calculate the total magnification, the magnification of the eyepiece lens and objective lens are multiplied together
Resolution
Resolution is the ability to distinguish between two separate points
If two separate points cannot be resolved, they will be observed as one point
The resolution of a light microscope is limited by the wave length of light
As light passes through the specimen, it will be diffracted
The longer the wavelength of light, the more that this diffraction will overlap as the points get closer together
Electron microscopes have a much higher resolution and magnification that a light microscope as electrons have a much smaller wave length than visible light
- This means that they can be much closer together before the diffracted beams overlap
Resolution Example - Phospholipid Bilayer
The concept of resolution is why the phospholipid bilayer of the cell membrane cannot be observed under a light microscope
- the width of the phospholipid bilayer is about 10nm
- the max resolution of a light microscope is 200nm (half the smallest wavelength of light, 400nm)
- any points that are separated by a distance less than 200nm (such as the 10nm phospholipid bilayer) cannot be resolved by a light microscope and therefore will not be distinguishable as separate
Light Microscope Summary
Used for specimens above 200nm
- light microscopes shine light through the specimen
- this light is then passed through an objective lens (which can be changed) and an eyepiece lens (x10) which magnify the specimen to give an image that can be seen by the naked eye
- the specimen can be living (therefore moving) or dead
- light microscopes are useful for looking at whole cells, small plant and animal organisms, tissues within organs such as in leaves or skin
Electron Microscopes Summary
Used for specimens above 0.2 or 0.5nm (both scanning and transmission)
- electron microscopes fire a beam of electrons at the specimen, either a broad static beam (transmission) or a small beam that’s moves across the specimen (scanning)
- the electrons are picked up by an electromagnetic lens which then shows the image
- due to a higher frequency of electron waves (a much shorter wave length) compared to visible light, the magnification and resolution is much better
- electron microscopes are useful for looking at organelles, viruses and DNA as well as looking at whole cells in more detail
- electron microscopy requires the specimen to be dead however this can provide a snapshot in time of what is occurring in the cell
- e.g. DNA can be seen replicating and chromosome position within the stages of mitosis are more visible
Light vs Electron Microscope Comparison
- L= small and easy to carry E= large and instillation means it can’t be moved
- L= no vacuum needed E= vacuum needed
- L= easy sample preparation E= complicated sample preparation
- L= up to x1500-2000 magnification E= over x50,000 magnification
- L= resolution 200nm E=0.2-0.5nm resolution
- L= specimen can be living or dead E= specimens are dead
