2.1 Microscopes And Cell Structure Flashcards
Dry mount
Section a whole specimen (cut very thin with sharp blade), place specimen in center of slide with cover slip over it (small specimens can be viewed without sectioning)
Specimen examples- hair, pollen, insect, muscle tissue
Wet mount
Specimen suspended in liquid like water/immersion oil, cover slip placed at 45 degree angle to minimize risk of artefacts (air bubbles) and flatten liquid out
Specimen examples- aquatic organisms
Squash slide
Wet mount prepared, lens tissue used to gently press down cover slip, for weak materials use 2 slides to press down cover slip
Specimen examples- root tip cells
Smear slides
Edge of slide used to smear sample creating thin, even coating on another slide, cover slip then placed over sample
Specimen examples- sample of blood (viewing blood cells)
Use of stains
Coloured chemicals that bind to molecules in a specimen making it easier to see, differential staining creates contrast/distinguishes between organisms and organelles as diff parts of a cell absorb more/less stain making them visible
Preparing a sample for staining
Must be dry, then heat fixed being passed through a flame, specimen will stick to slide and take up stains
Differently charged stains
Pos charged dyes attracted to neg charged chemicals leading to staining/Neg charged dyes repel the neg charged cytosol so they don’t stain
Use of gram staining technique
Separating bacteria into gram pos and gram neg
Describe gram staining technique
Crystal violet applied then iodine (to fix the dye), washed with alcohol- Gram pos retain crystal violet stain so appear blue/purple. Gram neg have thin cell walls so lose the stain, then stained with safranin dye (counter stain) and they appear red
Gram pos susceptible to the antibiotic penicillin (which inhibits cell wall formation), Gram neg aren’t susceptible due to thin cell walls
Use of acid fast technique
Differentiating species of mycobacterium from other bacteria
Describe acid fast technique
A liquid solvent carries carbolfuchsin dye into cells, then washed with dilute alcohol, mycobacterium not affected by alcohol so retain carbolfuchsin stain and turn red, other bacteria lose it and stain blue
Stages of slide preparation
Fixing- chemicals used to preserve specimens
Dehydrating- using alcohol to remove water
Sectioning- specimens dehydrated in alcohol are placed in a resin to form a hard block that can be sliced thinly
Staining- treated with stains to create contrast
Mounting- secured to slide and cover slip placed on top
Risks of stains
Many toxic or an irritant, so avoid skin/eye contact and wear gloves/goggles
Why do specimens need to be thin?
So you can see internal structures and so light passes through it
Magnification equation
Magnification= image size ÷ actual size
M=I÷A
What is magnification?
How much larger an object appears relative/compared to its original size
What is resolution?
The minimum distance between 2 objects in order for them to appear separate
Eyepiece graticule and stage micrometre
Graticule fitted to eyepiece lens micrometre placed on stage, line them up knowing each division on the micrometre is 0.1mm long, work out size of object
Parts of a light microscope
Eyepiece lens, course-focusing knob (larger), fine-focusing knob, body tube, objective lens (x4 x10 x40), specimen, stage and stage clips, condenser, light from mirror/lightbulb, arm, base
Advantages/disadvantages of light microscopes
Advantages:
Can observe living things, easy to set up and use, cheap, portable, no harsh chemicals used
Disadvantages:
Low magnification and resolution, 2D image (only able to see nucleus and chloroplast)
How does a light microscope work?
Light passes from bulb through specimen and is focused through objective and eyepiece lens for magnification
Advantages/disadvantages of transmission electron microscopes (TEM)
Advantages:
Very high magnification and resolution, 2D image but can see smaller organelles like lysosomes
Disadvantages:
Specimen must be dead as water would boil in vacuum, vacuum required, expensive, long to set up as very thinly sliced specimen
How does a TEM work?
Beam of electrons passed through specimen and focused to produce a 2D image
Advantages/disadvantages of scanning electron microscopes (SEM)
Advantages:
high magnification and resolution, 3D image (can see surface in detail)
Disadvantages Same as TEM, lower resolution and magnification however
How does a SEM work?
Reflected electrons are collected and focused on a viewing screen
