Analysis Of Cell Components Flashcards
How do you work out magnification?
Magnification = image size divided by
actual size
What do you need to make sure when working out magnification?
That all the units are the same ( either in mm or um ).
If you are trying to find the diameter of a cell is it the actual size or the image size?
It is the size of the real object / actual size
If you were given a micrograph with a scale bar drawn on it. How do you work out the actual size?
Eg |———-| = 10um ( specimen was 4 bars long )
Find how many times bigger cell is from scale bar.
Do this by measure scale bar and measure length of cell.
Cell divided by scale bar = (eg 4)
Do that number times by number on scale bar. 4 times 10um = 40um
What is image size measured in?
It is measured in mm
How do you know if it is the image or the actual size
Image size is what you measure with a ruler. Can be on scale bar or component in cell
Actual size is the diameter or the number next to scale bar or cell. Which is in um (eg. 20um)
How do you make TEM microscope 3D
2D black and white (photomicrograpgh)
3D look multiple section layers
How do SEM microscopes work?
Scan beam electrons across specimen
Beam bounces of surf and knocks of electrons from specimen
Electrons gathers in cathode ray tube
= image 3D
How are artefacts caused?
Inaccuracies when preparing
Eg. Squashing and straining sample
Why do scanning electron microscope have a 3D image
Because) electrons deflected/bounce off (using SEM)
Accept Resolution is lower (with SEM)
Before the cell was examined using the electron microscope, it was stained. This stain caused parts of the structure of the cell-surface membrane to appear as two dark lines.
Suggest an explanation for the appearance of the cell-surface membrane as two dark lines.
3’ marks
- Membrane has phospholipid bilayer;
- Stain binds to phosphate / glycerol;
- On inside and outside of membrane.
Accept phospholipid head / protein.
The image of flagellum used a SEM
The figure above is different from an image of this bacterium obtained using a TEM
Describe and explain one difference between these images
2 marks
Description -
3D with SEM and 2D with TEM
or
only surface visible SEM but internal structure visible TEM
Explanation (reason why) -
Because electrons deflect/ bounce off using SEM
Accept resolution is lower with SEM
Or
Electrons transmitted/ pass through with TEM
A student determined the size of the cell structure from a photograph obtained using a microscope
He used a ruler and a calculator and gave the answer in um
Describe how the student determined the size of the structure
2 marks
Mark in pairs: 1 and 2 OR 3 and 4
1. Measure (length of structure) and divide by magnification;
Accept correct equation making reference to a measurement
2. Correct conversion from measured length to um, either
× 10 000 from cm
OR
× 1000 from mm;
- Measure (length of structure) and divide by (image) length of scale bar;
- Multiply by actual length of scale bar;
Why would nucleus not be visible in image in electron microscope (1mark)
Nucleus not strained
Only a section/ slice so part of another of cell.
