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BIOLOGY
,CELL STRUCTURE
Types of microscopes
1. Light microscope
2. Electron microscope - Transmission Electron Microscope (TEM)2D
- Scanning Electron Microscopes (SEM)3D
Magnification (“x” sign placed in front of the object):
Number of times an image is enlarged, compared to actual size of the object
Resolution (1 Mm = 1x10^⁻6m) (nm or Mm):
The ability to distinguish the separation between two points seen under a microscope
- Increase in magnification (not equivalent to) increase in resolution
Resolution is determined by:
- Range of electromagnetic radiations of different wavelengths (electromagnetic spectrum)
- The shorter the wavelength used, the higher the resolving power
- Wavelength of visible light is longer than of an electron, the ability to distinguish between
two points is lower
Maximum resolution is the…
- Shortest distance between 2 points
- Max resolution = ½ wavelength used
- Longer wavelength = larger minimum distance need to distinguish points as separate = lower
resolution
- wavelength of visible light: 400-700 nm
- max resolution of light microscope = 200 nm (if smaller, it is blurry)
Light microscope
- Source of electromagnetic radiation: visible light
- Wavelength: approx. 400-700 nm (low energy long wavelength)
- longer wavelength than electron
- Focused using mirrors and glass lenses
- Highest magnification x1500
- Max resolution: 200 nm
Advantage: live specimens can be viewed, image can be coloured
Light microscope: micrometre (µm)
Electron microscope
- Source of electromagnetic radiation: free electrons
- Wavelength: approx. 1nm (high energy, short wavelength)
- Must be in a vacuum environment so electrons travel in straight lines
- Use electromagnetic lenses
- Highest magnification x250, 000
- Max resolution: 0.5 nm (high)
Disadvantage: only dead material, black and white
Electron microscope: nanometre (nm)
, Transmission electron microscope (TEM) Scanning electron microscope (SEM)
Beam of electrons Lower resolution compared to TEM
Passed to specimen before view Scan surfaces of specimens
2D 3D
Details: Internal structures, membranes
How do we measure cells?
Stage micrometer → is placed on the stage (big one), it shows the true value of length (usually
10mm in length with 100 small divisions), appears bigger when magnification increases
Eyepiece graticule (EPG) → is on the eyepiece lens (small one), shows 100 graticule units (100
EPG) which are in arbitrary units, always same size
1 EPG = mm/n.divisions
, CELLS
Types of cell
Eukaryote: an organism whose cells contain a nucleus and other membrane-bound organelles (found
in animals, plants, fungi)
Prokaryote: an organism whose cells does not contain a nucleus or other membrane-bound
organelles (bacteria)
EUKARYOTIC CELL
Cell surface membrane
● Function: controls movement of substances into and out of the cell
● Made of phospholipids bilayer
● Partially permeable
● 7nm thick
● Also known as plasma membrane
BIOLOGY
,CELL STRUCTURE
Types of microscopes
1. Light microscope
2. Electron microscope - Transmission Electron Microscope (TEM)2D
- Scanning Electron Microscopes (SEM)3D
Magnification (“x” sign placed in front of the object):
Number of times an image is enlarged, compared to actual size of the object
Resolution (1 Mm = 1x10^⁻6m) (nm or Mm):
The ability to distinguish the separation between two points seen under a microscope
- Increase in magnification (not equivalent to) increase in resolution
Resolution is determined by:
- Range of electromagnetic radiations of different wavelengths (electromagnetic spectrum)
- The shorter the wavelength used, the higher the resolving power
- Wavelength of visible light is longer than of an electron, the ability to distinguish between
two points is lower
Maximum resolution is the…
- Shortest distance between 2 points
- Max resolution = ½ wavelength used
- Longer wavelength = larger minimum distance need to distinguish points as separate = lower
resolution
- wavelength of visible light: 400-700 nm
- max resolution of light microscope = 200 nm (if smaller, it is blurry)
Light microscope
- Source of electromagnetic radiation: visible light
- Wavelength: approx. 400-700 nm (low energy long wavelength)
- longer wavelength than electron
- Focused using mirrors and glass lenses
- Highest magnification x1500
- Max resolution: 200 nm
Advantage: live specimens can be viewed, image can be coloured
Light microscope: micrometre (µm)
Electron microscope
- Source of electromagnetic radiation: free electrons
- Wavelength: approx. 1nm (high energy, short wavelength)
- Must be in a vacuum environment so electrons travel in straight lines
- Use electromagnetic lenses
- Highest magnification x250, 000
- Max resolution: 0.5 nm (high)
Disadvantage: only dead material, black and white
Electron microscope: nanometre (nm)
, Transmission electron microscope (TEM) Scanning electron microscope (SEM)
Beam of electrons Lower resolution compared to TEM
Passed to specimen before view Scan surfaces of specimens
2D 3D
Details: Internal structures, membranes
How do we measure cells?
Stage micrometer → is placed on the stage (big one), it shows the true value of length (usually
10mm in length with 100 small divisions), appears bigger when magnification increases
Eyepiece graticule (EPG) → is on the eyepiece lens (small one), shows 100 graticule units (100
EPG) which are in arbitrary units, always same size
1 EPG = mm/n.divisions
, CELLS
Types of cell
Eukaryote: an organism whose cells contain a nucleus and other membrane-bound organelles (found
in animals, plants, fungi)
Prokaryote: an organism whose cells does not contain a nucleus or other membrane-bound
organelles (bacteria)
EUKARYOTIC CELL
Cell surface membrane
● Function: controls movement of substances into and out of the cell
● Made of phospholipids bilayer
● Partially permeable
● 7nm thick
● Also known as plasma membrane
