Topic 3: Cell structure Flashcards
Why do we use electrons instead of light to see closer
Electrons have a shorter wavelength, and therefore can distinguish from things only 0.1nm apart
What is the order of units from km to nm
km , m , mm , um , nm
What is resolution
The minimm distance apart that two objects can be for them to appear as separate items.
Describe and explain the solution that you place the tissue you want to separate in
Cold - to reduce enzyme activity
Buffered- to limit the pH being affected
Isotonic - same water potential as the tissue to prevent osmosis
State the two stages of cell fractionation
- Homogenisation
- Ultracentrifugation
Describe Homogenisation
Cells are broken using a homogeniser (blender). This releases the organelles from the cell. The resultant fluid is called the homogenate, and is then filtered using a a gauze, to remove any complete cells and large debris
Describe Ultracentrifugation
- The tube of the filtrate is placed in the centrifuge, and spun at a low speed.
- The heaviest organelle are forced to the bottom, where they form a sediment/ pellet
- The supernatant fluid is removed, and spun again at higher speeds, so the next organelle are separated.
State the order of the organelles when they come out of the centrifuge
1, Nuclei
2, Chloroplasts
3, Mitochondria
4, Lysosomes
5, Ribosomes
Explain the two main advantages of using an electron microscope
1) The electrons have a shorter wavelength than light therefore they result in a higher resolution.
2) Electrons are negatively charged therefore the beam of electrons can be focused using an electromagnet
What are the two types of electron microscope (full name)
Transmission electron microscope
Scanning electron microscpe
Explain How the TEM works
Explain the limitations of the TEM
