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
Equation for magnification
Image size = Actual size x Magnification
Two types of microscope
Electron
Light
Cell first observed
1665 by Robert Hooke. Observed the structure of thinly sliced cork using an early light microscope. Described the compartments he saw as looking like ‘honeycomb and named these boxes ‘cells’.
Two types of electron microscope
Scanning (SEM)
Transmission (TEM)
Observed the first living cells
Antonie van Leeuwenhoek constructed a microscope with a single spherical lens in the late 1600s, that magnified up to x275. He was the first person to observe bacteria and protocista in his examinations of pond water
Advantages/Disadvantages of TEM
Advantages - Provide high resolution images
Disadvantages- Specimen need to be sliced thinly.
Who provided the first evidence for the origins of new plant cells?
Barthelemy Dumortier
Robert Brown, an English botanist was the first to observe which structure of a plant cell?
The nucleus
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.
What are the rules for producing good scientific drawings?
- Include a title
- State magnification
- Use a sharp pencil for drawings and labels
- Use white, unlined paper
- Use as much paper as possible for the drawing
- Draw smooth, continuous lines
- Do not shade
- Draw clearly defined structures
- Ensure proportions are correct
- Label lines must be parallel to the top of the page and drawn with a ruler. They must not cross or have arrow heads.