Cell structure and division Flashcards
What is the limitation of a light microscope?
Cannot distinguish two objects less than 0.2 um apart
How can an electron microscope overcome this?
Beams of electrons have shorter wavelengths
In terms of magnification, define ‘object’
The material put under the microscope
Define ‘image’
The way the material appears when viewed through the microscope
Define ‘magnification’
How many times bigger the image of an object is compared to its actual size
How do you find out magnification of an object?
Size of image/ Size of object
Define ‘resolution’
The minimum distance apart 2 objects must be in order to be distinguished from each other
What is cell fractionation?
Where cells are lysed and the contents separated
Why must the tissue be placed in cold, isotonic, buffered solution?
Cold - to reduce enzyme action
Isotonic - to prevent damage to organelles by osmosis
Buffered - to keep pH constant
What is used to break up cells?
Homogeniser
The fluid obtained is called:
Homogenate
How are the organelles in the homogenate separated?
By using an ultracentrifuge
What organelles are heaviest?
Nuclei
Where in the centrifuged tube are the heaviest cell components found?
At the bottom, in the sediment
What is the fluid at the top of the tube called?
Supernatant
What are the 2 main advantages of an electron microscope?
- Short wavelength
2. Beam can be focused using electromagnets
What special conditions must an electron microscope operate in?
Near vacuum
Why is this?
Molecules in the air can absorb electrons
2 types of electron microscopes are:
- Transmission electron microscope
2. Scanning electron microscope
How is the beam focused in a TEM?
A condenser electromagnet
Does the beam pass through the specimen?
Yes
Why do some parts of the specimen appear dark?
They absorb electrons
Limitations:
Vacuum
Process is complex and image is not coloured
Specimen must be very thin
Artefacts
In a SEM, does the electron beam come from above or below?
Below
