Microscopes

• The formula for microscopes is Actual size x Magnification = Image size
• To get from mm to micro metres times by 1000
• To get to micrometres to nanometres times by 1000
• Light microscopes can be used to look at cells and large organelles within the cell. Staining cells make organelles clearer
• Light microscopes are quick and easy to prepare, natural colour is observed and living tissue can be observed.
• Light microscopes only magnify objects up to 2000x and resolution is restricted.
• Dry mounts are when solid specimen are viewed whole or cut is slides. The specimen is placed on the slide and a cover slip is placed over
• A wet mount is when a specimen is suspended in a liquid e.g water. and a cover slip is paced on from an angle.
• A squash slide is when a wet mount is prepared first then a lens tissue is used to gently press down the cover slip.
• A smear slide is when the edge of a slide is used to smear the sample e.g blood, creating a thin even coating on the slide. A cover slip is then placed over the sample.
• Basic stain is used with methylene blue, crystal violet and safranin. They stain negatively charged molecules and strictures. The outcome is positive.
• An acidic stain is used with congo red dye which stains positively charged molecules and structures such as proteins. The outcome can be either positive or negative stain.
• Negative stains use india ink dye and nigrosis dye which stains the background not the specimen. The outcome is a dark background and a light specimen.
• Gram staining begins with crystal violet which stains the cells blue or purple. Then iodine mordant makes dye less soluble so it adheres to cell wall. Next alcohol decolorizer washes away stain from gram-negative cell wall. Gram-positive cells remain blue or purple, gram-negative cell are colourless. Finally safranin counter stains allow dye to adherence to gram negative cells. Gram positive cells remain purple and gram negative appear pink or red.
• There are two types of electron microscopes including the scanning electron microscope and the transmission electron microscope.
• The transmission electron microscope is when a beam of electrons passes through the specimen and is dispersed by structures. The scattered electrons are then captured on a photographic plate.
• The scanning electron microscope is used when the specimen is coated in a very thin layer of metal and a beam of electrons are bounced off the surface onto a photographic plate.
• The transmission electron is in 2D images, its max maginification is 2000000x and max resolution is 0.5nm. There is heavy staining and the specimens must be dead and viewed in a vacuum.
• The scanning electron miscroscope shows images in 3D, its max resolution is 3-10nm and max magnification is 500,000 x. There is no olour but can be artificially coloured. Specimen must be dead and viewed in a vacuum.
• A light microscope has a max resolution of 200nm a max magnification of 1500-2000x, we can see the natural colour, but it is viewed in 2D, it requires staining and the specimens can be dead or alive.
• Laser scanning confocal microscope

  • use laser beam to scan a specimen that has been tagged with fluorescent dye
  • dyed components give off light which is focused through a pinhole and onto a detecter
  • the detector connected to a computer which generates am image
• differential staining - using more than one chemical stain, which can be used to distinguish organelles