2.1.1 Microscopy

• Scientific Drawings Checklist


  Draw in pencil; Title the diagram with what the specimen is; Annotate whatever is visible; Do not sketch, colour in or shade; State the magnification.
• Crystal Violet Stain


  Used for gram staining; Crystal Violet is added, then iodine to fix the stain, alcohol washes away any unbound stain. Gram positive bacteria are stained because they have thicker peptidoglycan cell walls that absorbs the dye, so appears blue/purple. Gram negative bacteria have thinner cells walls and are stained red with safranin.
• Nigrosin/Congo Red

  Negatively charged so cannot enter the cell (cytosol repels them), and creates a stained background.
• Crystal Violet/Methylene Blue Stain

  Positively charged, so stains negatively charged materials.
• Smear Slide Preparation


  Used when examining blood cells in a blood sample. Created using the edge of another slide to smear the sample across another slide to create a smooth, thing, even coated sample. A cover slip is then placed on top.
• Squash Slide Preparation

  Used when creating a root tip squash sample to view the chromosomes in mitosis. Wet mounts which you squash the water under to ensure you have a thin layer to enable light to pass through.
• Wet Mount Slide Preparation

  When the specimens have water added to them before lowering the coverslip with a mounted needle to prevent air bubbles forming, used for aquatic organisms.
• Dry Mount Slide Prep

  Thin slices. The whole specimen is viewed with just the cover slip placed on top.
• Stage Micrometer


  A glass slide having precisely spaced lines etched at known intervals, inside the microscope.
• Eye Piece Graticule


  A transparent scale, usually with 100 divisions, which is placed in the microscope eyepiece so that it can be seen at the same time as the object to be measured. Changing the objective lens or the magnification means you need to recalibrate.
• Resolution


  The minimum distance between two objects in which they can still be viewed as separate.
• Magnification


  Refers to how many times larger an image is in comparison to the object. I=AM
• Laser Scanning Confocal Microscope


  Fluorescent microscope image, image is obtained as the microscope scans the specimens point by point using a focused laser beam to create a 2D image. A 3D image is obtained in different focal planes. As the light is emitted from the specimen it causes fluorescence. Scientists use this to view sections of tiny structures that would be challenging to physically section off.
• Scanning Electron Microscope (SEM)


  Specimens do not need to be thin as the electrons are not passing through it; the electron are beamed onto the surface and the electrons are scattered in different ways depending on the contours. The image is produced in 3D.
• Transmission Electron Microscope (TEM)

  Extremely thin specimens are stained and placed in a vacuum, and a beam of electrons passes through it. Some areas of the specimen absorbs the electrons and this makes them appear darker. The image is 2D and shows detailed images of the internal structure of cells.
• Electron Microscopes

  Determined by the wavelength of the beam of electrons. Higher magnification and resolutions because of the electron's short wavelengths. Image is obtained by using an electromagnet to focus the beam of electrons, and it must be in a vacuum, so only dead specimens can be examined (electrons are absorbed by air). The samples must also be stained. Two types.
• Light Microscopes

  Poor resolution due to its long wavelength of light. Living samples can be examined, and a colour image is obtained. Image is determined by the wavelength of light.