microscopes

• what is magnification?

  Magnification is how much bigger an image appears when englarged by a microscope compared to the original object viewed with the naked eye
• What is the equation that links image size, magnification and actual size?

  Image size = magnification x actual size
• What is meant by resolution?

  Resolution is the minimum distance between two objects in which they are still viewed as separate.
• what is the max magnification of a light microscope?

  1500 x
• What is the maximum magnification of a laser scanning/confocal microscope?

  1500 x
• What is the maximum magnification of a transmission electron microscope?

  2000000 x
• What is the maximum magnification of a scanning electron microscope?

  200000 x
• What is the resolution of a light microscope?

  200 nm
• What is the resolution of a laser scanning/confocal microscope?

  160 nm
• What is the resolution of a transmission electron microscope?

  0.1 nanometers
• What is the resolution of a scanning electron microscope?

  0.1 nm
• how do light/optical microscopes work?

  Optical microscopes shine a light through a sample, using lenses
• how do laser/confocal microscopes work?

  They use laser beams to analyse a sample, point by point, and produce an image using computer software
• What are light microscopes used for?

  To exame whole tissues and samples
• What are laser/confocal microscopes used for?

  They are used to look at different depths of a sample, making them useful in medical practise
• How do transmission electron microscopes work?

  A beam of electrons is passed through the sample, denser parts of the specimen absorb more electrons and appear darker
• How do scanning electron microscopes work?

  A beam of electrons is fired at the specimen- the beam knocks off electrons on the surface that it hits and the electrons that are delocalised are detected to produced a three dimensional scan
• how is resolution determined in an optical microscope?

  The wavelength of light
• How is resolution determined in an electron microscope?

  The wavelength of the beam of electrons
• what are the 4 types of slide preparation for light microscopes?

  Dry mount

  Wet mount

  Squash slide

  Smear slide
• what is a dry mount?

  When a slice or the whole specimen is viewed with just the cover slip placed on to of the specimen
• what is a wet mount?

  When water is added to the specimen just before placing the cover slip with a mounting needle to prevent air bubbles from forming.
• What type of organisms are used in wet mounts?

  Aquatic
• what is a squash slide?

  Wet mounts where you push down on the coverslip to squash the sample to ensure you have a thin enough layer for light to pass through.
• Give an example of when a squash slide is used?

  When creating a root tip sample to view the chromosomes in mitosis
• what is a smear slide?

  Smear slides are created usingthe edge of another slide to smear the sample across another slide to create a smooth, thin and evenly coated sample- a cover slip is added after the smear
• Give an example when smear slides are used?

  When viewing a blood sample.
• what is the formula for magnification?

  Magnification = size of the image / size of the object
• what is differential staining?

  A technique which involves many chemical stains being used to stain different parts of a cell in different colours
• what charge are crystal violet and methylene blue?

  Positively charged
• What are positively charged stains attracted to?

  Negatively charged materials
• What charge are Nigrosin and Congored?

  they are both negatively charged
• What is the significance of the negative charge of Nigrosin and Congo Red?

  They cannot enter the cells because cytosol repels them. This creates a stained background, and the unstained cells stand out.
• what two stains are used in gram staining?

  Crystal violet and safranin
• How do you stain a sample using crystal violet?

  The crystal violet dye is added, then iodine to fix the stain, then alcohol is used to wash away excess stain.
• How do gram positive bacteria look like after being stained with crystal violet?

  They appear blue or purple because the stain is retained due to the thicker peptidoglycen cell wall absorbing the dye.
• why cant gram negative bacteria not absrob crystal violet dye?

  Their peptidoglycen wall is too thin, so they do not retain the stain.
• why is gram staining important?

  it allows doctors to distinguish between the two types of bacteria and prescribe an appropriate antibiotic
• why must a sample for an electron microscope be be done in a vacuum?

  Air aborbs electrons