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Summary OCR A level Microscopy

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A detailed overview of microscopes both light and electron e.g. LCSM

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  • October 30, 2022
  • 6
  • 2022/2023
  • Summary
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TheHermitCrab
 Ribosomes – 70s – smaller than in eukaryotic cells
 Less than 2 micrometres

S IMILARITIES TO E UKARYOTIC CELLS
 plasma membrane
 cytoplasm
 ribosomes for protein synthesis
 DNA + RNA

DIFFERENCES TO EUKARYOTIC CELLS
 no nucleus
 no membrane bound organelles
 have 70s ribosomes
 cell wall made of peptidoglycan – not cellulose/chitin
 less well developed cytoplasm – no centrioles
 some bacterial cells also have a slime/waxy capsule, plasmids, flagella, pili

BINARY FISSION – BACTERIAL REPRODUCTION
 interact by means of a pilus
o thin appendage used to connect the two cells
1) Cell replicates its DNA
2) Cytoplasmic membrane elongates – separates DNA molecules
3) Cross wall forms – membrane invaginates
4) Cross wall forms completely
5) Daughter cells


MICROSCOPES
 Microscope – optical instrument used to produce an enlarged image of small
objects
 Object – material under microscope
 Image – appearance of object viewed through microscope

UNITS OF MEASURE
 millimetres (mm)
 micrometres (µm)
 nanometres (nm)
 1 metre – 1000mm
 1 mm – 1000 µm
 1 µm – 1000nm

MAGNIFICATION
 number of times larger an image appears compared to the size of the object
 microscopes produce linear magnification
o If the specimen is magnified x100 it's 100 times longer & wider than it
really is

CALCULATING MAGNIFICATION

, I
Magnification=Image ¿ ¿ Actual ¿ ¿ ¿ ¿ M=
A

 Nanometres & micrometres – usual units for magnification questions

RESOLUTION
 the clarity of the image
 the higher the resolution the clearer the image
 if the image isn't clear magnification won't help
 resolution - the ability of a microscope to distinguish two adjacent points as
separate from one another
 maximum resolution - the least distance between 2 closely opposed points at
which they may be recognised as 2 separate entities
 the better the resolution – the better you are able to view & identify finer
details
 High frequency
o Short wavelength
o Good Resolution
 Low frequency
o Long wavelength
o Poor resolution
 Resolution dependent on the wavelength of the beam we’re using to see the
material
 electron beam is able to provide better detail than light microscopes
o because of its shorter wavelengths
 as wavelength gets smaller – ability to resolve the spots gets better
 visible light has a longer wavelength than electron beams

LIGHT MICROSCOPE
 uses visible light & a system of lenses to magnify images
 simplest microscope
 cheap, easy to use, portable & can study whole specimens
 uses a number of lenses to focus a beam of light
 To view the specimens at different magnifications: - light microscopes have
3/4 objective lenses
o x4
o x10
o x40
o x 100 - oil immersion lens
o can be rotated in to position
o eyepiece lens then magnifies the image again - x10
 Total magnification = objective lens x eyepiece lens
 Max magnification = x1500
 Resolution = 200mm (resolution is limited).
 Specimens - a wide range of living organisms & sections of organisms can be
viewed
 Photomicrograph - photograph of the image seen with a light microscope

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