light microscope

• light microscope 


  -objective lens= placed near the specimen- magnifies the image (x4,10,40)

  -eyepiece lens= through which the specimen is viewed (x10)

  • inexpensive to buy and operate
  • small and portable
  • simple sample preparation
  • vacuum not needed
  • colour seen
  • specimens can be living or dead
• light microscope 


  -specimen must be thin so light can pass through

  -refractive index should be the same as the glass so the image isn't distorted

  -cover slip placed at an angle to prevent air bubbles.
• sample preparation 


  dry mounts= solid specimens viewed whole or cut into very thin slices= sector.

  wet mounts= specimen suspended in a liquid- cover slip placed at an angle to prevent air bubbles.dry mounts= solid specimen viewed whole or cut into very thin slices= sector.

  squash slide= similar to wet mounts, using lens tissue, gently press down on cover slip. Flattens soft tissue into single layer of cells, side by side.

  smear slides= used edge of one slide, smear sample over another slide, creating a thin, even coating place cover slip on top.
• differential staining 


  = can distinguish between 2 types of organisms that would otherwise be hard to identify.

  • crystal violet or methylene blue are positively charged dyes, which are attracted to negatively charged materials in the cytoplasm.
  • nigrosin and congo red are negatively charged and are repelled by the negatively charged cytosol. These dyes stay outside cells leaving the cells unstained, which stand out against stained backgrounds.
• gram staining 


  = used to separate bacteria into 2 groups- crystal violet is applied and appears purple.

  • gram positive= thick peptidoglycan layer and no outer lipid membrane.
  • gram negative= thin peptidoglycan layer and an outer lipid membrane.
  • iodine solution= enters cell wall and pores in nuclear membrane- visible.
• production of slides 


  -fixing= chemicals like formaldehyde are used to preserve specimens in as near- natural state as possible.

  -sectioning= specimens are dehydrated with alcohols and placed in a mould to form a hard block which can be thinly sliced.

  -staining= specimens are treated with multiple stains to show different structures.

  -mounting= specimens secured to a microscope slide and cover slip on top.