3.1->3.3 Microscope

Question 1

Magnification formula

Answer 1

size of image/ size of actual object

Question 2

Magnification

Answer 2

How many times bigger the image is compares to the actual object

Question 3

Resolution

Answer 3

The minimum distance apart that two objects can be in order for them to appear as separate items

Question 4

cm
mm
μm
nm

Answer 4

x 10
x 1000
x 1000

Question 5

resolving power of light microscope

Answer 5

2μm

Question 6

homogenation

Answer 6

cells are broken up by homogeniser, releasing organelles from cell
homogenate is then filtered to remove complete cells and large debris

Question 7

cell fractionation

Answer 7

tissue is placed is solution
homogenation
ultracentrifugation

Question 8

Conditions for solution tissue is placed in

Answer 8

cold- reduce enzyme activity that might break down organelles
same water potential as tissue- prevent organelles bursting or shrinking due to osmatic gain or loss of water
buffered- pH doesn’t fluctuate and alter structure of organelles or functioning of enzymes

Question 9

ultracentifugation

Answer 9

1. tube of filtrate is placed in centrifuge and spun at low speed(1000)
2. heaviest organelles(nuclei) are forced to the bottom of the tube, where they form a thin sediment or pellet
3. the fluid at the top of the tube(supernatant) is removed, leaving just the sediment of nuclei
4. supernatant is transferred to another tube and then spun in centrifuge at a faster speed(3500)
5. heavier mitochondria are forced to the bottom of the tube
6. supernatant is then transferred to another tube and spun at 16500
7. heavier lysosomes are forced to the bottom of the tube

Question 10

When was electron microscope developed

Answer 10

1930

Question 11

Advantages of electron microscope

Answer 11

1. short wavelength means high resolving power
2. Beam can be focused using electromagnets because electrons are negatively charged

Question 12

Conditions of electron microscope

Answer 12

a near vacuum has to be created within the chamber because electrons are absorbed or deflected by molecules in air

Question 13

How transmission electron microscope works

Answer 13

Electron gun produces beam of electrons underneath the specimen
It is focused on specimen by condenser electromagnet
It passed through a thin section of the specimen
Parts of the specimen absorb electrons and appear darker, whereas others allow it pass through and appear bright
An image is produced on a screen which can be photographed to give a photomicrograph

Question 14

Resolving power of TEM

Answer 14

0.1nm

Question 15

Why can resolving power of TEM sometimes not be achieved(2)

Answer 15

1. difficulty preparing specimen limit the resolution that can be achieved
2. the higher electron energy beam required may destroy the specimen

Question 16

4 limitations of TEM

Answer 16

1. whole system must be in a vacuum so no living specimen
2. complex staining process is required and then image is still not in colour
3. specimen must be extremely thin(creates 2d image)
4. image may contain artefacts

Question 17

Artefacts

Answer 17

Things that result from the way the specimen is prepared
They may appear on finished photomicrograph but aren’t part of natural specimen

Question 18

How scanning electron microscope works

Answer 18

Directs a beam of electrons onto the surface of specimen from above
The beam is passed back and forth across a portion of the specimen in a regular pattern
Electrons are scattered by the specimen, creating a pattern that depends on the contours of the specimens surface
Computer analysis of pattern of scattered electrons and secondary electrons produces can build a 3d image

Question 19

Resolving power of basic SEM

Answer 19

20nm