Analysis Of Cell Components

Question 1

Magnification formula

Answer 1

Magnification = size of image / size of object

Question 2

Resolution

Answer 2

Minimum distance apart that two objects can be for them to appear as separate items (depends on the wavelength or form of radiation used)

Question 3

Maximum magnification and resolution for an optical (light) microscope

Answer 3

x1500 and 0.2um

Question 4

Maximum magnification and resolution for an electron microscope

Answer 4

x1500000 and 0.1nm

Question 5

How do transmission electron microscopes (TEMs) work?

Answer 5

Electron gun produces a beam of electrons which are focused onto a specimen by a condenser electromagnet. Beam passes through a thin sections of specimen. Denser parts of the specimen absorb electrons and appear dark

Question 6

How do scanning electron microscopes (SEMs) work?

Answer 6

Beam of electrons scanned across the specimen, knocking off electrons from the specimen which are gathered in a cathode ray tube to form an image of the surface of the specimen (3D)

Question 7

TEMs disadvantages

Answer 7

• Specimen must be extremely thin to allow electrons to penetrate
• Complex staining process
• Colour images cannot be produced
• Living specimens cannot be observed (system is in a vacuum)

Question 8

SEMs disadvantages

Answer 8

• Lower resolution images than TEMs
• Complex staining process
• Colour images cannot be produced
• Living specimens cannot be observed (system is in a vacuum)

Question 9

Preparing microscope slides

Answer 9

• Pipette a small drop of water onto centre of slide
• Use tweezers to place a thin section of specimen on top of the water drop
• Use stain (eg. Iodine) to highlight organelles
• Lower cover slip using mounted needle

Question 10

What are microscope artefacts?

Answer 10

Things you can see down the microscope that aren’t part of the cell or specimen that you’re looking at (eg. Fingerprints)

Question 11

What are the steps of cell fractionation?

Answer 11

Homogenisation, filtration, ultracentrifugation

Question 12

Homogenisation

Answer 12

• Cut up the leaves
• Place in an ice-cold (to reduce activity of enzymes that break down organelles), buffered (to maintain pH, preventing enzymes denaturing), isotonic (to prevent damage to the organelles via osmosis) solution
• Grind the cells in a blender to break up the plasma membrane and release the organelles

Question 13

Filtration

Answer 13

• Filter homogenate through a gauze to separate any large cell debris or tissue debris from the organelles

Question 14

Ultracentrifugation

Answer 14

• Centrifuge filtrate at low speed
• Heaviest organelles (nuclei) get flung to bottom of the tube, forming the pellet
• Remaining organelles stay suspended in the supernatant
• Centrifuge supernatant and repeat process at higher speeds each time, until all organelles are separated out

Question 15

Using an optical microscope

Answer 15

• Clip prepared slide onto the stage
• Select the lowest magnification objective lens
• Use coarse adjustment knob to bring stage up to just below the objective lens
• Look down eyepiece (which contains ocular lens)
• Use coarse adjustment knob to move the stage downwards until the image is roughly in focus
• Adjust the focus with the fine adjustment knob until image is clear
• If need greater magnification, swap to a higher-powered objective lens and refocus

Question 16

How can you measure specimens under a microscope?

Answer 16

With an eyepiece graticule and a stage micrometre graticule