Microscopes Flashcards
How do you convert from millimetres to micrometers ??
X1000
How do you convert from micrometers to manometers ?
X1000
What is the resolution of a light microscope ??
0.17 micrometers or around 200 manometers.
What is he definition for magnification ?
How many times larger an image appears.
What is the definition for resolution ?
The minimum distance between two objects before they appear as one.
What are light microscopes often used to explore ?
Cell division or movement of cells.
Name some issues with Light microscopes.
You often need stain to see the cells and this can kill the cells.
How do lenses make an image visible in an optical/ light microscope ?
They converge the light rays to the specimen.
Compare the different views of a SCanning electron microscope and a transmission electron microscope.
SEM -3D
TEM - 2D
Compare how the SEM and TEM create images using electrons.
SEM - bounce off.
TEM- electron beam passes through a think sample. Passes through denser parts less easily creating contrasting black and white shades.
Compare the thickness of specimens used in SEMs and TEMs.
TEM needs to be thin.
SEM can be thick or thin.
Why is resolution often limited on an optical or light microscope ?
The wavelength of light is too long to resolve between close objects.
Compare the resolution of all 3 microscopes.
Light - low
SEM & TEM - high
Compare the types of specimens used in each microscope.
Light - living or dead
SEM & TEM - dead only
How is magnification calculated ?
Magnification = image length / actual length.
Explain how light microscopes and electron microscopes show a different image.
Electron microscopes only just a short beam of electrons which creates a high resolution.
Light microscopes use light - the wave length of light is often too long to distinguish between close together objects so a lower resolution image is shown.
Explain the meaning of resolving power.
The ability to distinguish between points which are close together.
Explain the reason for the difference in resolving power between light and electron microscopes.
Electrons have a shorter wave length. The wave length of light is too long to distinguish between close together points.
Care must be taken in interpreting electron micrograph a. Some features visible in an electron micrograph may not be present in a living cell. Explain why.
Processes involved in preparation alter and distort the contents of the cell.
Give one advantage of using a TEM rather than an SEM.
Higher resolution.
Name two structures in a eukaryotic cell that cannot be identified using a light microscope.
Ribosomes , Centrioles, ER, lysosomes.
Describe how you could make a temporary mount of a piece of plant tissue to observe the position of starch grains in the cells when using an optical light microscope.
Place one drop of water on a clean slide.
Take a thin slice of epithelial tissue from the plant using tweezers and place this on the slide ensuring this is completely flat.
Cover the specimen with a solution of iodine in potassium iodide.
Cover the specimens with a thin glass cube and wipe away any excess liquid on the slide.
Place the slide on the microscope stage and adjust the view.
Describe how you would use a microscope to find the mean diameter of triglyceride droplets on a cell.
Use an eyepiece graticule to accurately measure he radius of each triglyceride to 1 micrometer. Calibrate the graticule using a stage micrometer scale and repeat to calculate a mean.
Then divide the radius value for each triglyceride and divide this answer by the number of triglycerides investigated.
