Microscopes And cell fractionation

Question 0

What is resolution?

Answer 0

Resolution is how detailed the image is.
It is how well a microscope distinguishes between two points that are close together.

If a microscope cannot separate two objects, increasing the magnification won’t help.

Question 1

What is magnification?

Answer 1

Magnification is how much bigger the image is than the specimen you are looking at.

Question 2

How do you calculate magnification?

Answer 2

Magnification = length of image / length of specimen

Question 3

How do you go from nanometers to millimetres?

Answer 3

/ 1,000,000

Question 4

How do you go from micrometres to millimetres?

Answer 4

/ 1000

Question 5

How do you go from millimetres to nanometres?

Answer 5

X 1,000,000

Question 6

How do you go from micrometres to nanometres?

Answer 6

X 1000

Question 7

How do you go from millimetres to micrometres?

Answer 7

X 1000

Question 8

Put these in orders from smallest measurement to largest:

Micrometres, nanometres, millimetres

Answer 8

Nanometres
Micrometres
Millimetres

Question 9

What is the unit of micrometres?

Answer 9

um

Question 10

What is the unit of nanometres?

Answer 10

Nm

Question 11

What is the maximum resolution of light microscopes?

Answer 11

0.2 micrometres (Um)

Question 12

What is the maximum magnification of light microscopes?

Answer 12

X 1500

Question 13

Why do electron microscopes give a more detailed image than light microscopes?

Answer 13

They have a greater resolution.

Question 14

What is the maximum resolution of electron microscopes?

Answer 14

0.0001 micrometres (Um)

Question 15

What is the maximum magnification of electron microscopes?

Answer 15

X 1,500,000

Question 16

Why does electron microscopes have higher magnifications (and resolutions?) than light microscopes?

Answer 16

The wavelength of an electron is a lot shorter than light waves

Question 17

Disadvantages of electron microscopes?

Answer 17

Produce black and white images (can be coloured using computers)
Sometimes contain artefacts (dust and scratches) from preparing the specimen, affecting the clarity of the image

Question 18

How do transmission electron microscopes work?

Answer 18

They use electromagnets to focus a beam of electrons that are transmitted through the specimen. Denser parts of the specimen absorb more electrons, making them look darker on the image.

Question 19

How do scanning electron microscopes work?

Answer 19

They scan a beam of electrons across the specimen. This knocks off electrons from the specimen, which are gathered in a cathode ray tube to form an image. The image shows the surface of the specimen and they can be 3D.

Question 20

What are the advantages of TEMs?

Answer 20

Higher resolution images (than SEMs) so shows small objects

Question 21

What are the disadvantages of TEMs?

Answer 21

Can only be used on thin specimens

Can only be used in a vacuum so cannot be used on living organisms

Question 22

What are the advantages of SEMs?

Answer 22

Can be used on thick specimens

Can be 3D

Question 23

What are the disadvantages of SEMs?

Answer 23

Give lower resolution images (than TEMs)

Can only be used in a vacuum and so cannot be used on living organisms.

Question 24

Why can electron microscopes only be used in a vacuum?

Answer 24

Something I imagine to with other atoms affecting the electrons

Question 25

What is cell fractionation?

Answer 25

The process of looking at the organelles in a cell

Question 26

What are the three stages of cell fractionation?

Answer 26

Homogenisation
Filtration
Ultracentrifugation

Question 27

Describe homogenisation

Answer 27

Breaking up the cells

Vibrate of grind the cells
This breaks the plasma membrane, releasing the organelles into a solution
This must be kept ice cold to reduce the activity of enzymes that break up the organelles
This must be isotonic to prevent cells bursting or shrivelling due to osmosis

Question 28

Describe filtration

Answer 28

Solution of organelles filtered through a gauze, getting rid of the tissue debris (connective tissue). Organelles are smaller so they pass through

Question 29

Describe unltracentrifugation

Answer 29

This is the process of separating out organelles

The cell fragments are poured into a tube, this is put into a centrifuge (a machine that separates material by spinning). It is spun at a low speed. Heaviest organelles flung to the bottom, forming a sediment. The rest are suspended in supernatant. Supernatant is drained off into another tube and spun again at a higher speed, this process is repeated until all organelles are separated out.

Question 30

What is the weight of organelles from largest to lowest?

Answer 30

Nuclei 
Mitochondria
Lysosomes 
Endoplasmic reticulum 
Ribosomes

Question 31

What would you expect to find in the pellet two formed from the centrifuge?

Answer 31

Mitochondria

Question 32

What would you expect to find in the pellet one formed from the centrifuge?

Answer 32

Nuclei

Question 33

What would you expect to find in the pellet three formed from the centrifuge?

Answer 33

Lysosomes

Question 34

What would you expect to find in the supernatant three formed from the centrifuge?

Answer 34

Endoplasmic reticulum / ribosomes