Microscopy

Question 1

magnification def

Answer 1

The number of times larger an image is compared with real size of the object.

Question 2

Resolution def

Answer 2

the ability to distinguish between 2 seperate points. If two points cannot be resolved, they will be seen as one point.

Question 3

three types of microscopes

Answer 3

light, scanning electron microscope, transmission electron microscope

Question 4

Light microscope: uses and limitations

Answer 4

Uses- looking at cells and large organelles. Stain can be used to make the image clearer.
Limitations- magnification and resolution is limited

Question 5

light microscope - how it works, mag and res power

Answer 5

Works using visible light passed through the eyepiece and objective lens.Lowest magnification and resolution

Question 6

Electron microscopes - how it works and 2 types

Answer 6

A beam of electrons used to illuminate specimen. Vacuum inside machine ensures electrons travel in a straight line.
Types, SEM and TEM

Question 7

Electron microscopes benefits and limitations

Answer 7

benefits: can see details of organelles. Much higher resolution and magnification (compared to light microscopes)

limitation: very large, require specialist training and equipment, affected by magnetic fields, images in black and white, expensive, beam can damage specimen, preparation process can damage specimen
(list at least 3)

Question 8

Specimen in electron microscopes can be damaged from:

Answer 8

fixation using chemicals, staining with heavy metals, dehydration with solvents, samples may be fractured, samples may be set in resin. (list at least 3)

Question 9

Scanning Electron Microscope- how it works

Answer 9

• beam of electrons passed through specimen from above
• beam passed back and forth in a regular pattern
• electrons are scattered by contours of the specimen.
• computer converts the electron pattern into a 3D image

Question 10

Transition electron microscope- how it works

Answer 10

• electromagnets used to focus a beam of electrons which is transmitted on thin section of specimen
  -focused to produce an image
• denser parts absorb more electrons, appears darker on the image
  -other parts allow electrons to pass through, so appear bright.
• only thin specimens can be used
• 2D image produced
• highest magnification and resolution

Question 11

artefact def

Answer 11

Apparent structural detail, caused by processing of specimen, so is not legitimate (shouldn’t be there)

Question 12

artefact examples

Answer 12

air bubbles, loss in continuity of membranes, distortion of organelles, empty places in cytoplasm, mesosomes.

Question 13

conversion from centimeter (cm) to millimeter (mm)

Answer 13

x10

Question 14

conversion from mm to micrometers

Answer 14

x1000

Question 15

conversion from micrometers to nanometers

Answer 15

x1000

Question 16

Actual size=

Answer 16

image size/ magnification

Question 17

magnification=

Answer 17

image size/actual size

Question 18

image size=

Answer 18

actual size x magnification

Question 19

overall magnification

Answer 19

objective lens magnification x eyepiece magnification

Question 20

conversion from nanometre to micrometre

Answer 20

divide by 1000

Question 21

conversion from micrometere to millimetere

Answer 21

divide by 1000

Question 22

conversion from mm to cm

Answer 22

divide by 10

Question 23

what is the purpose of staining?

Answer 23

Increasing the contrast between different structures. sturctures take up cells in deifferent degrees.

Question 24

what is a positivley charged dye

Answer 24

• attatcted to negativey charged parts of the cell, leading to stained cell components

Question 25

2 exmaples of posotivley charged dyes

Answer 25

crystal violet and methalyne blue

Question 26

what charge is the cytoplasm

Answer 26

negativley charged

Question 27

what charge is the dna

Answer 27

postitivley charge

Question 28

what are negativley charged dyes

Answer 28

repelled by the cytosol, stay outside if the cells leaving the cells unsiatened and stain the background.

Question 29

example of negativley charged dye

Answer 29

congo red

Question 30

what is the purpose of differential staining

Answer 30

can distingish between two types of organisms or organlles within and organsism that woud otherwise be hard to identify
aka. counter staining

Question 31

what is the gram staining technique used for

Answer 31

used to seperate bacteria into gram positive and gram negative

Question 32

what is gram positive

Answer 32

thicker cell wall

Question 33

what is gram negative

Answer 33

thinner cell wall

Question 34

gram stain technique method

Answer 34

1.