Unit 2: Microscopy Flashcards
Specification reference 2.1.1
Define magnification
How much bigger the image is than the sample (specimen)
Define Resolution
How detailed the image is, it is the ability of a microscope to distinguish between to points that are close together
Two types of microscope
Electron
Light
Two types of electron microscope
Scanning (SEM)
Transmission (TEM)
Advantages/Disadvantages of TEM
Advantages - Provide high resolution images
Disadvantages- Specimen need to be sliced thinly.
Max Resolutions
Light microscope - 0.2 μm
TEM - 0.0005 μm
SEM - 0.003 - 0.01 μm
Lower resolution = better the image quality
Max Magnification
Light microscope - x1500
TEM - more than x1,000,000
SEM - less than x1,000,000 but stunning 3-D images
higher magnification the better
How does staining enable cell components to become visible?
Resolution is limited by wavelength of light and the diffraction of light as it passes through a sample. As most cell structures are normally transparent, images have low contrast as they do not absorb light. Stains increase the contrast as different components within the cells take up the stain to varying degrees, enabling components to become visible.
Give two examples of stains.
Methylene blue - positively charged dye, attracted to negatively charged materials in the cytoplasm - stains RNA/DNA
Congo red - negatively charged dye, that repels negatively charged cytosol. Stains outside of cell, leaving inside unstrained.
Eosin - The most common dye to stain used in histology, stains pink/orange. It is a negatively charged, acidic dye, that binds to basic components of a cell, mainly proteins located in the cytoplasm.
Iodine - Stain commonly used to observe plant cells.
Describe electron micrograph images
They are always black and white (but sometimes colour is added artificially to images don’t confuse this with staining).
What are the advantages and disadvantages of light microscopes?
Increase in magnification and resolution, both living and non-living, less magnification than electron
