2.1 Microscopy Flashcards
What is sectioning?
When specimens are dehydrated with alcohols and then placed into a mound with wax or resin to form a hard block, then sliced
What is fixing?
Using chemicals to preserve specimens in as near a natural state as possible
What is a dry mount?
When the specimen is placed in the centre of the slide and a cover slip is placed over the specimen
Hair, pollen, insect parts can be viewed whole this way
Muscle tissue or plants can be sectioned and viewed this way
What is a wet mount?
When the specimen is suspended in a liquid like water or immersion oil on the slide. The cover slip is then added slowly at an angle
Aquatic samples and other living organisms can be viewed this way
What are squash slides?
When a wet mount is first prepared and then a lens tissue is used to gently press down the cover slip
Potential damage to the cover slip can be avoided by squashing the sample between two microscope slides (depending on the material)
Root tip squashes are used to look at cell division
What are smear slides?
When the edge of a slide is used to smear the sample, creating a thin, even coating on another slide.
A cover slip is then placed on the sample
Blood is smeared to view the cells in blood
Why is staining used?
To make it easier to identify certain cell structures and organelles in a cell
To increase the visibility and contrast between cell components (there is often a lack of contrast and the cytosine is transparent)
How do you prepare a sample of staining?
- Place sample on slide and allow to dry
- Heat-fix the sample by passing it through a flame
- Specimen will then adhere to slope and take up stains
Which two dyes are positively charged?
Crystal violet
Methylene blue
How and what do positively charged dyes stain?
They are attracted to negatively charged materials IN THE CYTOPLASM, leading to the staining of CELL COMPOMENTS
What dyes are negatively charged?
Nigrosin
Congo red
How and what do negatively charged dyes stain?
They are repelled by the negatively charged cytosol
The dyes stay outside the cell, leaving the cells unstained, which then stands out against the stained background
This is a NEGATIVE STAIN TECHNIQUE
What is differential staining?
A staining technique that can distinguish between two types of organisms that would otherwise be hard to identify
Can also different between different organelles of a single organisms within a tissue sample
What is the gram stain technique?
A stain technique used to separate bacteria into two groups, Gram-positive and gram-negative
- Crystal violet is applied to bacterial specimen on slide
- Iodine is added to fix the dye
- Slide then washed with alcohol
- Gram-positive bacteria will appear blue/purple, gram- negative will lose stain because they have thinner walls
- Gram-negative will then be stained with safrain dye and appear red (counterstain)
What is the acid-fast technique?
A technique used to differentiate species of Mycobacterium from other bacteria
- Lipid solvent used to carry carbolfuchsin dye into cells being studied
- Then washed with a dilute acid-alcohol solution
- The Mycobacterium are not affected by the dilute acid-alcohol solution and retain the stain the bright red stain, whilst the other bacteria are exposed to methylene blue
