chemistry

CELL STRUCTURE
CELL THEORY:
Structural and functional unit of all living things
New cells arise from already existing cells
Cells contain information that instructs growth. This information can be passed onto new cells.

MICROSCOPES:
There are two main types of microscopes: Light and Electron
Electron Micrographs- shown in colour

LIGHT
ELECTRON
Uses beam of light
Magnification = x1500
Resolution = 200 nm
 Wide range of specimens can be used
 Samples are fairly quick + easy to prepare
 Cheaper and safer
 Limited resolution
 Limited magnification
Transmission Electron Microscope (TEM)
Scanning Electron Microscope (SEM)

Uses electromagnets to focus beam of electrons
Denser parts of specimen absorb more electrons creating contrast
Can only be used on thin specimens
Produces 2D image
Magnification = x500,000
Resolution = 0.2 nm
Scan beam of electrons across specimen
Beam bounces off surface of specimen
Produces 3D image
Magnification = x100,000
Resolution = 5 nm (lower)
Advantages
Disadvantages
 Can produce coloured images
 Better resolution
 Better magnification
 Must be used in a vacuum (no air)- electrons are absorbed by molecules in air
 Expensive
 Training is required
 Natural colours can’t be seen
 Dangerous- kills living cells

STAINING:
Used to have better visualisation of cells under a microscope
Used because some cell components are transparent
ACETIC ORCEIN- stains DNA dark red
GENETIAN VIOLET- stains bacterial cell walls
IODINE- stains starch granules
METHYLENE BLUE/EOSIN- used for light microscope
Specimen dipped in METAL like lead (metal ions scatter electrons to contrast)- used for electron microscope

SECTIONING:
Sections of tissue need to be cut into thin slices
Allows beam of light to pass through section of tissue
Specimens are embedded in wax
Makes it easier to identify tissue

CELL ORGANELLES:

ORGANELLE
STRUCTURE