CH2 microscopy Flashcards
What is a microscope
An object that enables you to magnify an object many times
Why is it useful to be able to see the individual cells that make up multicellular organisms
To have a greater understanding of how structure relates to function
What does cell theory state
- both plant and animal tissue is composed of cells
- cells are the basic unit of all life
- cells only develop from existing cells
How does a compound light microscope work
- has two lenses
- the objective lens is placed near to the specimen and the eyepiece lens through which specimen is viewed
- the objective/eyepiece lens configuration allows for much higher magnification and reduced chromatic aberration than a simple light microscope
How is a dry mount carried out
- solid specimens are viewed whole or cut into slices with a thin blade
- specimen is placed on centre of slide and cover slip is placed over sample
How is a wet mount carried out
- specimens are suspended in a liquid such as water or an immersion oil
- a cover slip is placed on from an angle
How is a squash slide carried out
A wet mount is first prepared and a lens tissue is used to gently press down on cover slip
How is a smear slide carried out
- edge of a thin slide is used to smear sample
- creates a thin and even coating on another slide
How does staining work
- increase contrast as different components within a cell take up stains to different degrees
- allows components to become visible so they can become identified
What is done to the sample before adding a stain
- sample is placed on a slide and allowed to air dry
- heat-fixed by passing through a flame
What are examples of positively charged dyes
- crystal violet
- methylene blue
What are examples of negatively charged dyes
- nigrosin
- congo red
What is the purpose of differential staining
To distinguish between two organisms that would otherwise be hard to identify
How is gram stain technique carried out
- separates bacteria into gram positive and gram negative
- crystal violet is applied to specimen on a slide and then iodine which fixes the dye
- slide washed with alcohol and gram positive retain stain and appear purple but gram negative lose stain
- stained with safranin which acts as a counterstain and negative bacteria appear red
How is acid fast technique carried out
- differentiates species of mycobacterium from other bacteria
- a lipid solvent carries carbolfuchsin dye into cells being studied
- cells are washed with dilute acid-alcohol solution and mycobacterium are not affected by acid-alcohol solution so retain red stain
- other lose stain and then exposed to methylene blue so appear blue
What are four stages involved in preparing slides
- fixing
- sectioning
- staining
- mounting
