Cells: Methods of studying cells Flashcards
What type of microscope would be used to see a living water flea specimen? Why?
- Optical microscope
- Specimen has to be living
What type of microscope would be used to see a pollen grain surface? Why?
- Scanning electron microscope
- Provides a 3D scan of the surface
What type of microscope would be used to view cristae in a mitochondrion? Why?
- Transmission electron microscope
- High resolution allows detail to be seen
What type of microscope would be used to view the stages of mitosis in a root cell? Why?
- Optical microscope
- Sample needs to be alive
What are the three types of microscopes?
- Optical microscope
- Scanning electron microscope
- Transmission electron microscope
What is the equation for mitotic index?
Mitotic index = Cells in mitosis / Total number of cells
What is the equation for magnification?
Magnification = size of image/size of real object
How do you convert mm (millimetre) into um (micrometre)?
x 1000
How do you convert um (micrometre) into nm (nanometre)?
x 1000
Give the three microscopic units in order of their size:
Millimetre (mm)
Micrometre (um)
Nanometre (nm)
How do you convert nanometre (nm) into micrometre (um)?
/ 1000
How do you convert micrometre (um) into milimetre (mm)?
/ 1000
Define resolution:
How detailed an image is.
How do transmission electron microscopes work?
Use electromagnets to focus a beam of electrons, which is then transmitted through the specimen.
Why do denser parts of a specimen appear darker through transmission electron microscopes?
Denser parts of the specimen absorb more electrons.
Give 1 advantage of TEM:
High resolution = so shows small objects
Give 2 disadvantages of TEM:
- Can only be used on thin specimens
- Can only be used on non-living specimens
Give 2 advantages of SEM:
- Can be used on thick specimens
- Can produce a 3D image
Give 2 disadvantages of SEM:
- Lower resolution than TEM
- Can only be used on non-living specimens
What are the three steps of cell fractionation?
1) Homogenisation
2) Filtration
3) Ultracentrifugation
What is the purpose of homogenisation in cell fractionation?
Breaks up plasma membrane and releases organelles into solution.
Why must the solution be kept ice-cold?
Prevent enzyme activity
Why must the solution be isotonic?
So the concentration of chemicals in the solution and organelles are same, to prevent the organelles being damaged.
Why must the solution contain a buffer?
To maintain the pH.
Explain the first step of cell fractionation, homogenisation:
1) Cell is broken up (e.g. in a blender) so plasma membrane is broken up.
2) Organelles are released into an ice-cold, isotonic, buffer solution.
Explain the second step of cell fractionation, filtration:
1) Homogenised cell solution is filtered through gauze to remove debris.
Explain the third step of cell fractionation, ultracentrifugation:
1) Cell fragments are poured into a tube. Tube is put into a centrifuge and is spun at a low speed.
2) Densest organelles (e.g. nuclei) sink first forming pellets and are removed.
3) Tube is spun again at a higher speed - process is repeated.
