These revision notes provide an in depth summary of this specific chapter of AQA Biology in the A Level Specification -
Very comprehensive notes and enabled me to achieve an A* in my A Level Biology exams.
- Cell is basic unit of life but with few exceptions cant be seen by naked eye
Microscopy
- Relatively long wavelength of light rays means light microscope can only distinguish
between two object if they are 0.2 μm, or further, apartm, or further, apart
- Limitation overcome by using beams of electrons rather than beams of light
- With shorter wavelength, beam of electrons in electron microscope distinguishes
between two objects 0.1 nm apart
Magnification
- Material put under microscope is known as the object
- Appearance of this material when viewed under microscope is known as the image
¿ image
Magnification =
¿ real object
- This can be rearranged to find the size of the real object if needed
- Important thing when dealing with magnification is the units of length that are used
o These are shown in the table below
Unit Symbol Equivalent in metres
Kilometre km 103
Metre m 1
Millimetre mm 10-3
Micrometre μm, or further, apartm 10-6
Nanometre nm 10-9
Worked example:
- Object measuring 100nm in length appears to be 10mm long in a photograph. What is
the magnification of the object?
¿ image 10 mm 10,000,000nm 1000
¿ object
= 100 nm
= 100nm
= 1
= x 100,000 times
Resolution:
- Minimum distance apart that two objects can be for them to appear as separate items
- Resolving power depends on wavelength or form of radiation used
- As said before, in light microscope resolution is 0.2 μm, or further, apartm
o Means objects > 0.2 μm, or further, apartm apart can be seen separately but objects < 0.2 μm, or further, apartm apart
will appear as a single item
- Greater resolution means greater clarity – image produced is clearer and more precise
- Increases magnification increases size of image but not always resolution
- Every microscope has a limit of resolution
o Up to this point increasing magnification will reveal more detail but beyond this
point increasing magnification will not do this
Object will appear larger but will be more blurry
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