Microscopy

Question 1

What are the pros and cons of a light microscope?

Answer 1

Pros: cheap, portable, easy to use, can study living specimens.
Cons: limited magnification, poor resolution

Question 2

what is a scanning electron microscope used for?

Answer 2

viewing the surface of objects under high magnification and resolution

Question 3

What is magnification?

Answer 3

is the extent to which an object has been enlarged

Question 4

What is resolution?

Answer 4

the ability to distinguish between two individual points as separate

Question 5

what is a transmission electron microscope used for?

Answer 5

observing the internal ultrastructure of cells under high magnification and resolution

Question 6

what are the pros and cons of an electron microscope

Answer 6

pros: very high magnification and excellent resolution
Cons: specimen has to be dead, very large, very expensive, needs great skills and training to use

Question 7

what is the difference between a transmission and a scanning electron microscope?

Answer 7

TEM sends a beam of electrons through the specimen, the SEM bounces the electrons off the surface

Question 8

what is an eye piece graticule?

Answer 8

a small ruler fitted to a light microscope’s eyepiece, it must be calibrated using a stage micrometer before being used to measure specimens.

Question 9

what is a stage micrometer?

Answer 9

a millimeter long ruler etched onto a slide, it has 100 divisions, each of 0.01mm or 10micrometers. it is used to calibrate the eyepiece graticule.

Question 10

why do we stain specimens?

Answer 10

to provide more contrast and make it easier to distinguish certain parts

Question 11

what is differential staining?

Answer 11

is a technique which involves many chemical stain being used to stain different parts of a cell in different colours

Question 12

what is the formula to calculate magnification?

Answer 12

Magnification = Image size/ actual size

Question 13

What are the maximum magnification of the different microscopes?

Answer 13

Light : 1,500X
SEM : 100,000X
TEM : 500,000X

Question 14

what are dry mounts?

Answer 14

are when thin slices or whole specimens are viewed, with just the coverslip placed on top eg plant tissue or hair

Question 15

what are wet mounts?

Answer 15

are when the specimen is suspended in a liquid such as water or an immersion oil. a coverslip is placed on from an angle. aquatic samples are best viewed this way

Question 16

what are squash slides?

Answer 16

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

Question 17

what are smear slides?

Answer 17

the edge of a slide is used to smear the sample, creating a thin even coating of the specimen. this is used to examine blood cells in a blood sample.

Question 18

what is gram staining?

Answer 18

it is another use of differential staining in examining bacteria. two different stains are used crystal violet and safranin.
Crystal violet binds to gram-positive bacteria making them appear blue/purple.
Safranin turns the gram-negative bacteria red.

Question 19

what does a scientific drawing need?

Answer 19

• draw in pencil
• title the diagram
• state the magnification/scale bar
• annotate visible cell components
• do not sketch/shade
• straight non overlapping labels