studying cells

Question 1

what is magnification equation?

Answer 1

. I
A M

Question 2

how do light microscopes work?

Answer 2

they pass a beam of light through a thin sample
- use glass lenses to focus images

Question 3

what is magnification?

Answer 3

how enlarged an image is

Question 4

what is resolution?

Answer 4

the minimum distance apart that two objects can be distinguished as separate objects

Question 5

advantages of optical microscopes

Answer 5

• cheap
• produce colour images
• easy to use
• can view live specimens

Question 6

disadvantages of optical microscopes

Answer 6

• low resolution
• low magnification
• specimens must be thin
• stains required

Question 7

Why do electron microscopes have a higher resolution than a light microscope?

Answer 7

as electrons have a shorter wavelength than the wavelength of light

Question 8

total magnification equation

Answer 8

objective magnification x eyepiece magnification

Question 9

how do electron microscopes work?

Answer 9

use a beam of electrons in which pass through/over the surface of a sample

Question 10

why are EM greyscale?

Answer 10

• some areas absorb electrons more than others
• heavy metal stains are used

Question 11

why must EM specimens be dead?

Answer 11

as they are viewed in a vacuum

Question 12

how are TEM images made?

Answer 12

by passing a beam of shorter wavelength electrons through a sample, creating 2D images

Question 13

how are SEM images made?

Answer 13

by passing a beam of shorter wavelength electrons across the surface of a sample, creates 3D images

Question 14

advantages of EM

Answer 14

• high resolution so can view smaller organelles
• high magnification

Question 15

disadvantages of EM

Answer 15

• more complex + expensive
• greyscale images
• artefacts common
• specimens must be dead

Question 16

what is cell fractionation?

Answer 16

process in which different parts and organelles of a cell are separated so that they can be studied

Question 17

what are the cells prepared in?

Answer 17

placed in a ice cold, isotonic, buffer solution

Question 18

why ice cold?

Answer 18

to reduce enzyme activity to prevent organelle damage

Question 19

why isotonic?

Answer 19

to make the concentration of chemicals the same as the cell to prevent damage by osmosis and shrinkage/ lysis of cells

Question 20

why buffer?

Answer 20

to maintain constant pH to avoid enzymes/proteins being denatured

Question 21

homogenisation

Answer 21

• BREAKING = cells broken up by either grinding or vibrating them. Cells blended in ice cold, isotonic, buffer solution
• FILTRATION = homogenised mixture of buffer and cell debris/ organelles is filtered, only organelles pass into filtrate, cell debris filtered out

Question 22

ultracentrifugation

Answer 22

solution placed into a tube and is centrifuged to separate organelles based on density. A pellet of organelles is left at the bottom of the tube and the supernatant is removed. Each time this is repeated at increasing speeds until the pellet of organelles you want is left

Question 23

order of organelle density

Answer 23

Nuclei
Chloroplasts
Mitochondria
Endoplasmic reticulum
Ribosomes