Topic 2: methods to study cells Flashcards
Name 3 key types of microscope
- Optical (light)
2.Scanning electron 3.Transmission electron.
Define magnification
How many times larger the image is compared to the object.
Define resolution
The minimum distance between two objects in which they can still be viewed as separate. The resolution in an optical microscope is determined by the wavelength of light, and the wavelength of the beam of electrons determines the resolution of an electron microscope.
Why do light microscopes have a poor resolution?
Light microscopes have a poor resolution due to the long wavelength of light.
Why are small organelles in a cell are not visible using
an optical microscope?
They are too small to be visible due to the wavelength of light limiting the resolution and have a lower magnification too.
Give the formula for magnification
Image size = Actual size x Magnification
I=AM
Describe optical microscope
What creates the image?
Beam of light
Condenser
Glass lens condense the beam
Resolution
Poor resolution
Magnification
Lower magnification
Colour image or not
Colour images
Types of samples
You can view living samples
Describe electron microscope
What creates the image?
Beam of electrons
Condenser
Electromagnets condense the beam
Resolution
High resolution
Magnification
Higher magnification
Colour image or not
Black and white images
Types of samples
Samples must be in a vacuum so cannot be living
Outline the stages for cell fractionation:
Cells are broken down so that the organelles are free to be separated. This is done using a homogeniser, a blender.
Once the cell has been broken open, the solution must be filtered to remove larger pieces of debris.
Explain why the solution must be:
Isotonic:
to prevent any movement of water by osmosis resulting in organelles shrivelling or bursting.
Explain why the solution must be:
Buffered:
to prevent pH changes. This is to prevent damage to organelles and enzymes.
to prevent pH changes. This is to prevent damage to organelles and enzymes.
explain why the solution must be ice cold
to reduce enzyme activity to prevent the breakdown of cell components.
Outline the stages of ultracentrifugation to separate the nuclei, mitochondria/chloroplasts, lysosomes and SER/RER and ribosomes:
Supernatant after the first spin at low speed- pellet contains the nuclei.
Supernatant after the second spin at medium speed- pellet contains mitochondria and chloroplasts (if a plant cell).
Supernatant after the third spin at high speed- pellet contains lysosomes and SER/RER.
Supernatant after the fourth spin at very high speed- pellet contains ribosomes
