Cell Structure and Division- Analysis of Cell Components Flashcards
What is magnification?
How much bigger the image is than the specimen
How is magnification calculated?
Magnification= image size/actual size
What is resolution?
How detailed the image is and how well a microscope distinguishes between two points that are close together
How do optical microscopes form an image?
By using light
What is the maximum resolution of an optical microscope?
About 0.2 micrometers so optical microscopes can’t be used to view organelles smaller than this such as ribosomes, the endoplasmic reticulum, lysosomes, mitochondria in detail
What is the maximum useful magnification of an optical microscope?
About x1500
How do electron microscopes view an image?
By using electrons
How does the resolution of electron microscopes compare to optical microscopes?
Electron microscopes have a higher resolution so give a more detailed image
What is the maximum resolution of electron microscopes?
About 0.0002 micrometers- about 1000 times higher than optical microscopes
What is the maximum useful magnification of an electron microscope?
About x1500000
What are the two types of electron microscope?
Transmission electron microscope and scanning electron microscope
How do TEMs view an image?
Use electromagnets to focus a beam of electrons which is then transmitted through the specimen
Which parts of the specimen will absorb more electrons in TEMs?
Denser parts of the specimen absorb more electrons which makes these areas look darker on the image
What is an advantage of TEMs?
They give high resolution images so that you can see the internal structure of organelles
What is a disadvantage of TEMs?
They can only be used on thin specimens
How do SEMs view images?
Scan a beam of electrons across the specimen which knocks off electrons from the specimen and are gathered in a cathode ray tube to form an image
How are images shown from SEMs?
Show the surface of the specimen and they can be 3D
What is an advantage of SEMs?
Can be used on thick specimens
What is a disadvantage of SEMs?
Give lower resolution images than TEMs
How do you prepare a ‘temporary mount’ of a specimen on a slide?
- Pipette a drop of water onto the slide
- Use tweezers to place a thin section of specimen on top of water drop
- Add a drop of a stain which is used to highlight objects in a cell
- Add cover slip- stand slip upright on slide next to water droplet, carefully tilt and tower it to cover specimen, try not to get any air bubbles as they’ll obstruct view of specimen
What is the purpose of cell fractionation?
Separate organelles from the rest of the cell
What are the three steps in cell fractionation?
Homogenisation (breaking up the cells), filtration (getting rid of big parts), ultracentrifugation (separating organelles)
How can homogenisation be done?
Vibrating the cells or grinding cells up in a blender
What happens in homogenisation?
Breaks up the plasma membrane and releases organelles into solution
Why must the solution be kept ice-cold?
Reduce the activity of enzymes that break down organelles
Why must the solution be isotonic?
Should have the same concentration of chemicals as cells being broken down to prevent damage to organelles by osmosis
Why should a buffer solution be added?
To maintain the pH
What happens in filtration?
Homogenised cell solution is filtered through a gauze to separate any large cell debris or tissue debris from organelles
How does filtration work?
Organelles are much smaller than the debris so they pass through the gauze
What is the process of ultracentrifugation?
- Cell fragments are poured into a tube which is put into a centrifuge and spun at a low speed. Heaviest organelles form pellet at bottom of tube and rest of organelles form supernatant at top of tube
- Supernatant is drained off, poured into another tube and spun in centrifuge at a higher speed. Heaviest organelles form pellet, supernatant is drained off and spun at an even higher speed in centrifuge
- Process repeated at higher and higher speeds until all organelles are separated out
What is the order of organelles from heaviest to lightest?
Nuclei, mitochondria, lysosomes, endoplasmic reticulum, ribosomes
