Cells-Methods of studying cells Flashcards
What are the limitations of a light microscope?
Lower magnification and resolution (0.2um).
What is magnification?
How many times bigger the image produced by the microscope is compared to the real-life object.
What is the equation for magnification?
magnification= image size/object size
What is resolution?
The ability to distinguish between two objects that are close together.
What are the two different types of electron microscope?
Transmission electron microscope and scanning electron microscope.
What is the maximum resolution of an electron microscope?
0.2 nm
How does a transmission electron microscope work?
A beam of electrons passes through a thin section of a specimen. Denser parts of the specimen absorb more electrons, meaning they appear darker on the final image.
What are the advantages of TEM’s?
They give high resolution images which allows the internal structures within cells to be seen.
What are the disadvantages of TEM’s?
- Can only be used with very thin specimens
- Cannot be used to observe live specimens as it takes place in a vacuum.
- Doesn’t produce a colour image.
- Requires lengthy treatments to prepare specimens, which means that artefacts can be introduced.
How does a scanning electron microscope work?
A beam of electrons passes over the specimen and the electrons scatter and are detected, creating an image.
What are the advantages of SEM’s?
- Can be used on thick or 3d specimens
- Allows the external structure of specimens to be observed.
What are the disadvantages of SEM’s?
- Gives lower resolution images than TEM
- Cannot be used on live specimens
- Doesn’t produce a colour image
What are the properties of the solution tissues must be placed in before homogenisation?
- Ice cold to reduce the activity of enzymes that break down organelles.
- Isotonic (same water potential as cells) to prevent water from moving into the cells via osmosis.
- Buffered to prevent organelle proteins from becoming denatured.
What is the process of homogenation?
Cells are blended in a homogeniser to form a homogenate, breaking them up.
What is the process of ultracentrifugation?
The homogenate is placed in a centrifuge and spun at a slow speed. A sediment of the nuclei (heaviest organelles) forms at the bottom and the supernatant is removed. This is then placed in a different tube and spun at a slightly faster speed. This continues until all organelles are seperated out.
