2.1.3 methods of studying cells

Question 1

what is magnification

Answer 1

number of times greater an image is than the size of the actual object

Question 2

what is the equation for magnification

Answer 2

size of image/size of real object

Question 3

what is resolution

Answer 3

minimum distance apart 2 objects which can be distinguished as separate objects

Question 4

what are the three different types of microscope

Answer 4

• optical
• transmission electron microscope
• scanning electron microscope

Question 5

how are microscopes focused

Answer 5

• optical = light is focused using glass lenses
• TEM and SEM = electrons focused using electromagnets

Question 6

how do microscopes work

Answer 6

• optical = light passes through specimen, different structures absorb different amounts and wavelengths
• TEM = electrons pass through specimen, denser parts absorb more and appear darker
• SEM = electrons deflected off specimen surface

Question 7

what type of image do microscopes create

Answer 7

• optical and TEM = generates 2D image of cross section
• SEM = generates 3D image of surface

Question 8

what is the resolution of microscopes

Answer 8

• optical = low resolution due to long wavelength of light
• TEM = very high resolution due to short wavelength of electrons
• SEM = high resolution due to short wavelength of electrons

Question 9

what structures can you see with microscopes

Answer 9

• optical and SEM = cant see internal structure of organelles or ribosomes
• TEM = can see internal structure and ribosomes

Question 10

how does the specimen have to be when using a microscope

Answer 10

• optical = thin
• TEM = very thin
• SEM = doesnt need to be thin

Question 11

what is the magnification of microscopes

Answer 11

• optical. = low magnification ( x1500 )
• TEM and SEM = high magnification ( x1,000,000 )

Question 12

can you view living organisms with microscopes

Answer 12

• optical = yes
• TEM and SEM = can only view dead/dehydrated specimens as uses a vacuum

Question 13

what is the preparation like to use a microscope

Answer 13

• optical = simple
• TEM and SEM = complex preparation so artefacts often present

Question 14

can microscopes show colour

Answer 14

• optical = yes
• TEM and SEM = no

Question 15

describe how to convert between different units

Answer 15

metres x1000, millimetres x1000, micrometer x1000, nanometer

Question 16

describe how the size of an object viewed with an optical microscope can be measured

Answer 16

1. line up eye piece graticule with stage micrometer
2. calibrate eye piece graticule - use stage micrometer to calculate size of divisions on eye piece graticule
3. take micrometer away and use graticule to measure how many divisions make up the object
4. calculate size of object by multiplying number of divisions by size of division
5. recalibrate eye piece graticule at different magnifications

Question 17

what are the 4 steps of cell fractionation and ultracentrifugation used to separate cell components

Answer 17

1. homogenisation
2. place in cold isotonic buffered solution
3. filter homogenate
4. ultra centrifugation

Question 18

what is the step of homogenisation

Answer 18

homogenise the tissue using a blender to disrupt the cell membrane, breaking open the cells and releasing organelles

Question 19

why is the solution cold, isotonic and buffered

Answer 19

cold = to reduce enzyme activity so organelles are not broken down
isotonic = so water doesnt move in or out of organelle by osmosis so they dont burst
buffered = to keep pH constant so enzymes dont denature

Question 20

what is the step of filtering the homogenate

Answer 20

removing large unwanted debris eg. whole cells or connective tissues

Question 21

what is the step of ultracentrifugation

Answer 21

separates organelles in order of density/mass:
- centrifuge homogenate in a tube at high speed
- remove pellet of heaviest organelle and respin supernatant at higher speed
- repeat at increasing speeds until separated out, each time pellet made of lighter organelles

Question 22

what is the order of organelle mass ( heaviest to lightest )

Answer 22

• nuclei
• chloroplasts/mitochondria
• lysosomes
• ER
• ribosomes