Microscopy

Question 1

State the resolutions for the 4 types of microscopes

Answer 1

Light: 200nm
TEM: 0.5nm
SEM: 3-10nm
Laser Scanning Confocal: 200nm

Question 2

State the magnifications for the 4 types of microscopes

Answer 2

Light: x2000
TEM: x500,000
SEM: x500,000
Laser Scanning Confocal: x1000-2000

Question 3

Why would a scanning electron microscope be used?

Answer 3

Gives 3D image & cell surfaces can be seen

Question 4

Why would a transmission electron microscope be used?

Answer 4

Gives 2D image and allows organelles to be seen

Question 5

Magnification Equation

Answer 5

Image size = Actual size x magnification

Question 6

Difference between magnification & resolution

Answer 6

Magnification is the number of times bigger the image is compared to the object whereas the resolution is the degree to which is it possible to distinguish between 2 points

Question 7

How does a compound light microscope work?

Answer 7

2 lenses

objective lens is closest to specimen
eyepiece lens is how the specimen is viewed

Objective lens produces a magnified image which is magnified again by the eyepiece lens

Question 8

Sample Preparation: Dry Mount

Answer 8

Solid specimens are viewed whole or cut thinly

Specimen places on the centre of the slide & covered by cover slip

used for: Pollen, dust etc

Question 9

Sample Preparation: Squash Slides

Answer 9

Wet mount prepared

lens tissue is used to press down the cover slip

used for: soft samples

Question 10

Sample Preparation: Wet Mount

Answer 10

Specimens suspended in liquid
Cover slip placed on angle

Used for: Aquatic samples

Question 11

Sample Preparation: Smear slides

Answer 11

Edge of slip is used to smear sample

Cover slip placed over

used for: Blood

Question 12

Why is staining used?

Answer 12

Increased contrast between organelles (take up the stain to different degrees)

Question 13

Gram Stain Technique

Answer 13

separation of bacteria
Gram positive and gram negative

Crystal violet is applied to to specimen
then iodine
slide is washed with alcohol

gram positive bacteria retain crystal violet and will appear blue/purple

gram negative have thinner walls so lose the stain
counterstained using safranin dye
= appear red

Question 14

Features of light microscopy

Answer 14

Inexpensive
Small & portable
Simple slide preparation
Vacuum is not required
up to x2000 magnification
Specimens can be dead or alive

Question 15

Features of electron microscopy

Answer 15

Expensive
Large
Complex sample preparation
Vacuum is required
x500,000 magnification
specimens have to be dead