4.1.1.5 Microscopy

Question 1

How do you calculate cell magnification from an image?

Answer 1

Magnification = Image Size/Actual Size

Question 2

Disadvantages of an electron microscope:

Answer 2

• Can only observe a dead specimen as it has to be observed in a vacuum and will die as there is no oxygen
• Expensive - £1 million
• Have to have training to use it – expert preparation
• (Maintenance costs)
• Black and white (but can add artificial colouring)
• Attached by magnetic fields
  
  • Can’t use phone in the same room

Question 3

Advantages of an electron microscope:

Answer 3

• Higher magnification (up to x2,000,000)
• Higher resolution (o.1nm)
• Can see inside of the cell – better for observing details
• Using a beam of electrons instead of a beam of light allows the electron microscope to gain a much higher resolution in seeing much smaller objects e.g. mitochondria, chloroplasts, ribosomes, plasmids

Question 4

Disadvantages of a light microscope:

Answer 4

• Lower magnification (around x200)
• Lower resolution(200nm)
• Can only see the outside of the cells and nucleus

Question 5

Advantages of light microscopes:

Answer 5

• Mobile/portable
• Colour
• Can view a living specimen
• Cheaper - £200 - £300
• No complex lighting system needed
• With light microscopes large sub cellular structures can be seen

Question 6

Magnification:

Answer 6

the ability of a lens or other optical instrument to magnify (enlarge) the size of something in an optical image

Question 7

total magnification =

Answer 7

Total magnification = magnification of eyepiece (fixed 10x) x magnification of objective lens (4x, 10x, 14x)

Question 8

Resolution:

Answer 8

• The ability of a microscope to distinguish between 2 adjacent points as separate from one another
• Maximum resolution is the smallest distance between two points at which they may be recognised as two separate entities
• The better the resolution, the better you’re able to view and identify details

Question 9

What are the two types of electron microscope?

Answer 9

• Scanning Electron Microscope (SEM)
  
  • electrons scan the surface of a sample
• Transmission Electron Microscope
  
  • electrons penetrate a sample - can see inside a sample

Question 10

Explain how electron microscopy has increased understanding of sub-cellular structures:

Answer 10

• An electron microscope has a much higher magnification and resolving power
• This means it can be used to study cells in much more detail
• Scientists can now see (and better understand) sub-cellular structures

Question 11

centimetres (cm) to millimetres (mm)

Answer 11

x10

Question 12

millimetres (mm) to micrometres (µm)

Answer 12

x1000

Question 13

micrometres (µm) to nanometres (nm)

Answer 13

x1000

Question 14

How do you calculate the order of magnitude?

Answer 14

• Convert to same unit
• Put in standard form
• Find difference between powers

Question 15

Labelled diagram of a microscope:

Answer 15

Question 16

What can be use to judge the relative size or area of sub-cellular structures?

Answer 16

estimations