microscopy

Question 1

what does microscopy allow us to do?

Answer 1

-microscopy allows us to visualise biological specimens that are otherwise invisible to the human eye

Question 2

what is a micrograph

Answer 2

a high resolution magnified image of the specimen

Question 3

definition of magnification

Answer 3

how much bigger the image appears compared to the size of the object

Question 4

definition of resolution

Answer 4

the clarity of the object, how well a microscope distinguishes between two points that are close together

Question 5

light microscopes
key features

Answer 5

-use a beam of light, focused by lenses to produce an image
-cheap, easy to use and can study whole living specimens
-poor resolving power due to long wavelength of light
-max resolution is 200nm
-cannot be used to visualise ribosomes as they are 2nm wide.
cannot produce images clearly if they magnify images any higher
max mag - 1500x

Question 6

laser scanning microscopes
(confocal miscropes)
key features

Answer 6

-laser scanning microscopes use a high powered beam of light to create an image
laser passes over each point in the specimen and computer assmbles the pixel information into one image
can be used to study whole living specimens
-more expensive than light microscopes but have a higher resolution to show high contrast.
has depth selectivity feature meaning can focus on structures at different depths within the specimen and can be used to visualise whole living specimens
max resolution= 160nm
max magnifcation= 1500x

Question 7

electron microscopes
key features

Answer 7

• a beam of electrons fired from a cathode and focused on the specimen by magnets
  -electron beam has a shorter wavelength than visible light (0.004nm) therefore images are produced with a higher resolution
  specimens must be coated in metal and placed into a vacuum, so electron microscopy can only be used to view dead cells.

Question 8

definition of a photomicrograph

Answer 8

photograph of a specimen viewed using a optical microscope

Question 9

definition of an electron micrograph

Answer 9

photograph of a specimen viewed using an electron microscope.

Question 10

transmission electron microscopy
how is the image formed

Answer 10

the electron beam travels through the specimen to a detector below creating a 2d black and white image
samples are chemically fixed by dehydration and stained with metal salts before being placed into a vacuum.
very thin sample to allow electrons to penetrate.

Question 11

scanning electron microscopy

Answer 11

the electron beam hits the specimen and is scattered into a detector creating a 3d image
the specimen is coated with a fine film of metal

Question 12

properties of microscopes
light microscopes (optical microscopes)

Answer 12

medium= light beam with a long wavelength between 400nm - 700nm
preparation- simple preparation
dimensions= 2D
max mag= 1500x
max resolution= 200nm
image= coloured
can be used to view whole living cells

Question 13

properties of microscopes
confocal microscopes

Answer 13

medium- high powered light beam
preparation= simple preparation
dimensions= 3D
max mag= 1500x
max resolution= 160nm
image= coloured
can be used to view whole living specimens
has depth selectivity feature meaning can view structures at different depths within the specimen and an be used to visulise whole living specimens

Question 14

properties of microscopes
transmission electron microscopes (TEM)

Answer 14

medium= electron beam
preparation- samples are chemically fixed by dehydration and stained with metal salts before being placed in a vacuum
very thin sample to allow electrons to penetrate
dimensions= 2D
max mag= 2,000,000
max resolution=0.1nm
image- black and white but computer software can add false colour

can be used to view dead cells only

Question 15

properties of microscopes
scanning electron microscopes

Answer 15

medium- electron beam
preparation- coated with a fine film of metal
dimensions+ 3D
max mag= 200,000x
max resolution= 20nm
image- black and white
electron beam hits the specimen and is scattered into the detector forming a 3D image
can only be used to study dead cells

Question 16

advantages of light microscopes

Answer 16

-cheap
-easy to use
-can be used to view whole living specimens providing an insight to processes and behaviour of microscopic organisms
-minimal training required
-can produce coloured images

Question 17

disadvantages of light microscopes

Answer 17

-poor resolving power of 200nm due to long wavelength of light which is between 400nm- 700nm.
-produces 2d images
-cannot produce images clearly if they magnify images higher

Question 18

disadvantages of electron microscopes

Answer 18

-both are very large
-expensive
-require alot of training
-require great skill
-can only be used to view dead cells as samples must be placed in a vacuum.

Question 19

advantages of electron microscopes

Answer 19

-much higher resolution wavelength of (0.004nm) has a shorter wavelength than light meaning images produced are of a higher resolution.

Question 20

what is staining

Answer 20

staining is a technique where dye is used to highlight cells and cell structures making them easier to visualise in a microscope.

Question 21

stains binding or collecting around different molecules to view cell components is known as diffrential staining.

Answer 21

staining works by binding to different types of molecules or cell structures this also allows different components of cells to be identified. this is known as differential staining.

Question 22

acetic orcein

Answer 22

binds to DNA allowing chromosomes and nuclei to be visualised

Question 23

eosin

Answer 23

binds to cytoplasm

Question 24

sudan red

Answer 24

binds to lipids

Question 25

iodine stains:

Answer 25

starch granules dark purple and cell walls yellow.

Question 26

what is light interference and why may some light microscopes use it

Answer 26

light interference produces a clear image of a colourless transparent specimen without staining. other use a dark background against which a illuminated specimen can be seen