Topic 2 - Microscopes Flashcards
What is the formula for magnification?
Magnification = size of image/size of real object
What is magnification?
How much bigger the image can be enlarged compared to its actual size
What is resolution?
The ability to distinguish between two objects as separate. Defined as the minimum distance at which two objects can still be seen as distinct.
What is the limiting factor of resolution?
The wavelength of light limits resolution which cannot resolve structures smaller than 0.2 µm
What are the uses of a light microscope?
Suitable for observing life specimens and used for general cellular observations.
How do electron microscopes work?
– They use a beam of electrons focused by electromagnets.
– Operate in a vacuum to prevent air particles from scattering the electrons.
– Can resolve objects a small as 0.1 nm providing a much greater resolution than light microscopes.
What are the two types of electron microscope and what is the difference?
Transmission electron microscope (TEM): a beam of electrons passes through a specimen and produces a detailed 2-D image of the internal structure areas absorbing more electrons appear darker.
Scanning electron microscope: a beam of electrons scans, the surface of the specimen and produces a detailed 3-D image of the specimens surface.
What is the main advantage of the TEM?
Extremely high resolution for internal details.
What is the main advantage of the SEM?
Produces 3-D images useful for understanding surface textures.
What are the limitations of transmission electron microscopes?
- require a vacuum so living specimens cannot be observed.
- a complex staining process is required which may introduce artefacts.
– Specimens must be thin.
– SEM has a lower resolving than TEM but both are far superior light microscope.
Compare the light and electron microscopes.
Source of light is visible light - electrons
Resolution is 0.2 µm - 0.1 nm
Magnification is up to x1500 - up to x2000000
Simple specimen preparation can view live samples- complex specimen cannot view live samples
Image produced is @-D - @-D or £-D
What are the guidelines for drawing a scientific diagram?
- use a sharp pencil to clear lines
- Avoid shading or colouring
- Ensure diagrams are large and clear
- Labels structures with straight lines not crossing one another
How should you label your scientific diagram?
- include the name of the specimen and magnification used
- label should: be horizontal and include specific terms.
- use a scale bar to indicate actual size
How should the proportions be done on a scientific diagram?
- Accurately represent the relative size of structures
- Use grid paper if necessary to maintain proportions.
How would you prepare the specimen to identify starch grains in a plant cell?
– A thin section of the plant tissue is prepared and placed on a slide.
– A drop of iodine solution is added to the tissue to stain the grains.
– The slide is covered with a cover slip and observed under a light microscope.
How would you be able to detect starch grains in a plant cell?
– When iodine binds to start grains the grains turn blue – black
– The colour change is due to the formation of an iodine starch complex
What three steps should you ensure for microscope calculations?
- Make sure the units are consistent; convert the measurements to the same unit
- Apply the formula; use the given data to calculate the required value
- Label answers; always include correct units in your answer
The image of a cell measures 50 mm and the magnification is x500. What is the actual size of the cell?
50 mm/500 = 0.1 mm
0.1 mm = 100 nm
