2.1 - cell structure

Question 1

define magnification

Answer 1

describes how much bigger an image appears compared with the original object

Question 2

whats the formula for magnification

Answer 2

image size / actual size

Question 3

define resolution

Answer 3

is the ability to distinguish between two points that are close together on an image

Question 4

what are the 3 types of microscopes?

Answer 4

• light microscope
• transmission electron microscope (TEM)
• scanning electron microscope
  (SEM)

Question 5

what are the properties of a light microscope ?

Answer 5

• uses light
• images produced in colour
• shown in 2D
• low magnification
• low resolution

Question 6

what are the properties of a SEM ?

Answer 6

• scans a beam of electrons across a specimen - this knocks off electrons from the specimen and the reflected electrons are collected to create an image
• shown as 2D
• no colour
• high magnification and resolution
• resolution lower than TEM

Question 7

what are the properties of a TEM ?

Answer 7

• uses electromagnets to focus a beam of electrons, transmitted through a specimen - denser parts absorb more electrons so appear darker in image
• 2D
• no colour
• high magnification and resolution
• higher resolution than SEM
• used on thin specimens

Question 8

what are the 4 ways to prepare a slide for light microscopes ?

Answer 8

• dry mount
• wet mount
• squash slide
• smear slide

Question 9

what is a dry mount ?

Answer 9

when thin specimens are viewed, with just the coverslip placed on top e.g hair /plant tissue

Question 10

what is a wet mount ?

Answer 10

when thin specimens have got water added to them before lowering the coverslip without air bubbles forming

Question 11

what is a squash slide ?

Answer 11

are wet mounts which you then push down on the coverslip to squash the sample to ensure you have a thin layer to enable light to pass through

Question 12

what is a smear slide ?

Answer 12

are created using the edge of another slide to smear the sample across another slide to create a smooth thin specimen. a coverslip is placed on top after smearing. e.g - blood cells

Question 13

what is an eyepiece graticule ?

Answer 13

its fitted on to the eyepiece - its a transparent ruler with numbers but no units

Question 14

what is a stage micrometer ?

Answer 14

its placed on the stage - it is a microscopic slide with an accurate scale (it has units) and its used to work out the value of divisions on the eyepiece graticule at a particular magnification.

Question 15

how do you calibrate an eyepiece graticule ?

Answer 15

• line up the eyepiece graticule and the stage micrometer
• each division on the stage micrometer is 0.1 mm long
• you count how many eyepiece graticule divisions fit into one stage micrometer division
• then to work out the size of one division on the eyepiece graticule you have to do 0.1 / the number of divisions on the eyepiece graticule that fit into one stage micrometer division
• eyepiece divisions = 1 stage division

Question 16

what are common stains used for light microscopes ? and what are they used for ?

Answer 16

• methylene blue
  stains DNA
• eosin
  stains cell cytoplasms

Question 17

whats the purpose of stains ?

Answer 17

they allow the object being viewed under a light microscope to be seen - different stains make different things show up - stain is taken up by some parts of the object more than others - the contrast makes the different parts show up

Question 18

whats the conversion from cm to mm and from mm to um and from um to nm