Microscopes

Question 1

What are the principles of a light microscope ?

Answer 1

-long wavelength light shone on specimen

Question 2

What can you see with a light microscope?

Answer 2

Nucleus
Nucleolus
Cell membrane
Cytoplasm

Question 3

Advantages of a light microscope

Answer 3

-colour images can use living samples

Question 4

Disadvantages of a light microscope

Answer 4

-lower resolution due to long wavelength of light
lower magnification
-smaller organelles in cells are not visible
-max magnification is x1500
-max resolution is 0.2 micrometers

Question 5

What are the principles of a scanning electron microscope?

Answer 5

-scans electrons across surface of objects
-knocks of electrons which are gathered by cathode to form

Question 6

What can you see with a scanning electron microscope?

Answer 6

Surface of a specimen eg shape of cell

Question 7

Advantages of an SEP

Answer 7

Higher magnification
Higher resolution
Details on image (texture and 3d depth )
Thick specimens

Question 8

Disadvantages of an SEP

Answer 8

[samples must be in a vacuum ]
Lower resolution than TEM(20nm)

Question 9

What are the principles of a transmission electron microscope?

Answer 9

Beam of electrons focused by electromagnet

Some parts absorb elements and appear dark

Extremely thin specimens

Question 10

What can you se with a TEM?

Answer 10

Chloroplasts,mitochondria ,Golgi, E.R, ribosomes ,lysosomes, cell wall

Question 11

Advantages of a TEM

Answer 11

Higher resolution than light microscope due to shorter wavelength of electron beam

Question 12

Disadvantages of TEM

Answer 12

Need a vacuum so can’t view living specimens

Complex staining process

Black and white image

Very thin specimens needed

Image contains artefact

Question 13

Define magnification

Answer 13

How many time larger rhe image is compared to the object

Question 14

Define resolution

Answer 14

Minimum distance between two objects in which they can still be wirewed as separate

Question 15

How many millimetres in a metre?

Answer 15

0.001
10^-3

Question 16

How many micrometers in a metre?

Answer 16

0.000001
10^-6

Question 17

How many nanometres are in a metre ?

Answer 17

0.000000001
10^-9

Question 18

Magnification calculation

Answer 18

Image/actual

Question 19

Resolution define resolution

Answer 19

The resolution or resolve in power of microscope is a minimum distance apart that two objects can be in order for them to appear as separate items

Question 20

What is necessary to study the structure and function of various organelles?

Answer 20

In order to study the structure and functions of the various organelles make up cells is necessary to obtain large numbers of isolated organelles

Question 21

Define cell fractionation

Answer 21

The process where cells are broken up the different organelles they contain are separated out

Question 22

What is the tissue placed in before cell fractionation can begin ?

Answer 22

Before cell fractionation can begin the tissue is placed in a cold buffered solution of the same water potential as the tissue

Question 23

Describe the solution for cell fractionation

Answer 23

-cold-to reduce enzyme activity that might break down the organelles

-is of the same water potential as the tissue – to prevent organise bursting or shrinking as a result of osmotic gain or loss of water

-buffered-so that the pH does not fluctuate. Any changed in pH could alter the structure of the organelles or affect the functioning of enzymes

Question 24

What are the two stages of cell fractionation?

Answer 24

Homogenation
Ultracentrifugation

Question 25

Describe homogenation

Answer 25

Cells are broken up by a homogeniser

Releases the organelles from the cell

Resultant fluid known as homeogenate is then filtered to remove any large piece of debris

Question 26

Describe ultracentrifugation

Answer 26

It’s the process by which the fragments in the filtered homegenate are separate in a machine called a centrifuge

This spins tubes of homeogenate at very high speed in order to create a centrifugal force

Question 27

What is the ultracentrifugation process for animal cells.

Answer 27

Tube of filtrate is placed in the centrifuge and spin at slow speed

Heaviest organelles, the nuclei are forced to the bottom of the tube where they form a thin sediment or pellet

Fluid at the top of the tube(supernatar) is removed leaving just sediment of nuclei

The supernatar is transferred to another tube and spun in the centrifuge at a faster than before

The next heaviest organelles the mitochondria are forced to the bottom of the tube

The process is continued in this way so that at each increase in speed the next heaviest organelle is sedimented and separated out

Question 28

How do you measure the size of objects using a light microscope ?

Answer 28

Eyepiece graticule

Question 29

Why can the scale in the eyepiece graticule not be used directly to measure the size of objects under a microscope?

Answer 29

Each objective lens will magnify to a different degree-the graticule must.first be calibrated for a particular objective lens -once calibrated in this way the graticule can remain in position for further use provided the same objective lens is used

Question 30

What do you need to use to calibrate an eyepiece graticule ?

Answer 30

You need to use a special microscope slide called a stage ,micrometer

Question 31

How do you calculate the scale for different kinds objective lenses?

Answer 31

Divide it by however many times bigger the magnification is