What is magnification
is how many times larger an image is than the real object
What is resolution
Is the ability to see detail ; the ability to see two objects as individual entities.
What is a light microscope ?
-uses visible light to illuminate a thin section of a sample
- energy’s transmitted
- uses stains eg iodine
- max resolution x200nm
- max magnification x1500
-coloured image
Adv- can look at living cells , cheap, can see in colour , portable , little training to use
Dis- low resolution , low useful magnification
What’s a transmission electron microscope?
-lets you look at a very thin cross section of an object 2D
- uses an electron beam
- energy’s transmitted
- stains used eg lead , uranium
- max resolution 0.1nm
- max magnification x1,000,000
Adv-high resolution image , high useful magnification
Dis- can’t study living material , costly to set up , requires training to use , only see in black and white
What is a scanning electron microscope?
- lets you look at the surface of objects at Hugh resolution 3D
- uses electron magnets
- energy reflected
- stain used eg gold , platinum
- max resolution 10nm
- max magnification x500,000
adv- high resolution image,high useful magnification
Dis- there costly , only see in black and white, requires training , can’t study living molecules
What’s a laser scanning confocal microscope?
- use a laser light to scan an object point by point and assemble by computer the pixel information onto one image displayed on a computer screen 3D
- energy’s reflected
- staining used eg fluorescent molecules / antibodies
- max resolution 200nm
- max magnification x1500
Adv- image 100percent focused , can look at living molecules
Dis- can only see flurocent objects , low resolution , expensive
Explain gram staining technique?
- used to separate bacteria into 2 groups
1- crystal violet is first applied to the bacteria specimen on a slide then iodine which fixes the dye. - wash slide with alcohol
- gram positive remain crystal violet
2- gram negative bacteria have thinner cell walls therefore lose the stain
- stained with saffron dye
- bacteria will appear red
- gram + are susceptible to the antibodies penicillin which inhibits info of cell walls
gram- have much thinner cell walls that arnt susceptible to penicillin
What is staining ?
- they allow us to see the cells structure and allow us to provide a contrast
Magnification equation
Magnification = image size / actual size
Meters -> millimetres -> micrometers-> nanometres
m x1000= mm x1000= Mn x 1000= nm
Dry mount
Dry mounts are when thin slices of whole specimens are viewed with just the coverslip placed on top eg plant tissues or hair
Wet mounts
Are when water is added to the specimen before lowering the coverslip with a mounted needle to prevent air bubbles from forming. Aquatic organisms could be viewed this way.
Squash slides
Are wet mounts which you then push down on the coverslip to squash the sample to ensure you have a thin layer to enable light to pass through . This is used when creating a root tip squash sample to view the chromosomes in mitosis
Smear slides
Are created by placing a drop of the sample at one end of the slide and using the edge of another slide ( held at an angle ) to smear the sample across the first slide to create a smooth , thin even coated specimen . A cover slip is placed on top after smearing. This is used when examing blood cells in a blood sample .
Staining in light microscopy
• Crystal violet or methylene blue are two stains commonly used. They are positively charged, and therefore are attracted to and stain negatively charged materials.
• Nigrosin and Congo red are negatively charged, and therefore cannot enter the cells as cytosol repels them. This creates a stained background, and the unstained cells then stand out.
