CH2 different types of microscopes

Question 1

How does an electron microscope work

Answer 1

• A beam of electrons with a wavelength of less than 1nm is used to illuminate the specimen
• produce images with magnifications up to 500000 times

Question 2

What is a transmission electron microscope

Answer 2

• beam of electrons transmitted through specimen and focused to produce an image
• resolving power of 0.5nm

Question 3

What is a scanning electron microscope

Answer 3

• beam of electrons is sent across surface of specimen and reflected are collected
• resolving power of 3-10nm
• produces 3d images

Question 4

How are samples prepared for electron microscopes

Answer 4

• fixed using chemicals or freezing
• dehydrated with solvents
• TEM is set in resin and stained again
• SEM may be fractured to expose inside and coated with heavy metals

Question 5

What is an artefact

Answer 5

• visible structural detail caused by processing the specimen and not the specimen
• in light microscopes include the bubbles caused by cover slip
• in electron microscopes include the loss of continuity of membranes,empty spaces in cell cytoplasm

Question 6

How does laser scanning confocal microscopy work

Answer 6

• single spot of focused light is moved across a specimen which causes fluorescence from components labelled with a dye
• emitted light is then filtered through a pinhole aperture
• only light close to focal plane is detected
• spot illuminating specimen is moved across specimen and a two dimensional image is produced

Question 7

How does atomic force microscopy work

Answer 7

• gathers information by feeling surface with a mechanical probe
• consists of a sharp tip used to scan service, when brought close to surface forces between tip and specimen cause deflections of cantilever which are measured using a laser beam reflected from the top of the cantilever into a detector