2.1 Microscopy Flashcards
cell theory
Both plant and animal tissue is composed of cells
cells are the basic unit of all life
cells only develop from existing cells
Galileo Galilei
1609
Said to have developed the first true or compound microscope
His instrument was the first to be given the name ‘microscope/
First type of microscopes developed in 16th to 17th century.
Robert hooke
Cells first observed
coined the term cell for the structure he saw
1665
Anton von Leeuwenhoek
First living cells observed
First to observe bacteria and protoctista
went on to observe red blood cell, sperm cell and muscle fibres
1674-1683
Barthelemy Dumortier
Evidence for theorigin of new plant cells
first to observe cell division in plants
1832
Robert brown
nucleus of a plant first observed
1833
Theoder Schwann
the birth of universal theory
“all living things are composed of cells and cell products”
1837-38
Robert Remak
evidence of the origin of new animal cells
first to observe cell division in animals
Louis Pasteur
spontaneous geration disproved
demonstrating that bacteria would only ggrow in a sterile nutrient broth after it had been exposed to air
How a light microscope works
A compound light microscope has 2 lenses
1) objective (placed near the specimen)
2) eyepiece (through which the specimen is viewed)
the objective lens produces a magnfied image which is further magnified by the eyepiece lens.
allows for higher magnification
illumination is usually provided by a light underneath the sample
opaque specimens can be illuminated from above with some microscopes
dry mount
Solid specimens are viewed whole or cut into very thin slices (sectioning).
Specimen is placed on the centre of the slide.
Cover slip is placed over the sample.
E.g. hair, pollen, dust,insect parts.
Sectioned: muscle tissue, plants.
wet mount
Specimen is suspended in a liquid (water or an immersion oil).
Cover slip is placed on from an angle.
E.g. aquatic samples and other living organisms can be viewed.
smear slide
Edge of slide is used to smear the sample,
Creating a thin, even coating on another slide.
Cover slip is placed on top.
E.g. sample of blood.
squash slide
Wet mount is first prepared.
Lens tissue is used to gently press down cover slip (may cause damage to specimen).
Press down using a slide.
E.g. soft sample: root tip squashes.
why do we use staining
Staining increases contrast
Differentiate between organelle
And cells.
preparing a slide for staining
Sample is placed on slide
Allow to air dry
Heat fixed by passing through flame
Specimen would adhere to slide
Will then take up stains.
negative stain technique
Positive
Dyes: Crystal violet and methylene blue
Attracted to negatively charged part of the cytoplasm
Negative
Dyes: Nigrosin and congo red
Repelled by negatively charged cytosol.
Leaves cells unstained compared to stained background, providing clear contrast.
differential staining
Able to distinguish between :
- 2 types of organisms that are hard to identify
= different organelles of a single organism within a tissue sample.
gram stain technique
Used to separate bacteria into two groups.
Gram positive bacteria and gram negative bacteria.
- Crystal violet is first applied to a bacterial specimen.
- Then iodine, which fixes the die.
- The slide is then washed with alcohol.
Gram positive bacteria: retain the crystal violet stain and will appear blue or purple under a microscope.
Gram negative bacteria: have thinner cell walls and therefore lose the stain.
- They are then stained with safranin dye, which is a counterstain
These bacteria will then appear red.
Gram positive bacteria: susceptible to the antibiotic penicillin, which inhibits the formation of cell walls.
Gram negative bacteria: much thinner cell walls that are not susceptible to penicillin.
definition:
- fixing
- staining
- sectioning
- mounting
Fixing - chemicals are used to preserve specimens in as near natural state as possible
Staining- specimens are often treated with many stains to show different structures.
Sectioning - specimens are dehydrated with alcohols
placed in a mould with wax/resin to form a hard block
sliced thinly using a knife
Mounting - the specimens are then secured to a microscope slide and a cover slip is placed on top
acid fast tecnhique
Used to differentiate between species of Mycobacterium from other bacteria.
- A lipid solvent is used to carry carbolfuchsin dye into the cells being studied.
- The cells are then washed with dilute acid-alcohol solution.
Mycobacterium:
- are not affected by the acid-alcohol
- retain the carbolfuchsin dye
- which is bright red.
Other bacteria:
- lose the stain
- are exposed to a methylene blue stain
- which is blue.
Good scientific drawing
Include a title of what the specimen is
State the magnification of the drawing
Use a sharp pencil on plain white paper
Draw smooth continuous lines
Do not shade
Clearly label all structures
Ensure proportions are correct
Label lines should be drawn with a ruler, should not cross and have no heads
end of 2.1
