cell structure

Question 1

how far apart do two objects need to be for a light microscope to distinguish between them?

Answer 1

0.2um or further

Question 2

when do convex glass lenses work more effectively?

Answer 2

if used in pairs in a light microscope

Question 3

which has shorter wavelength/beams electrons or light?

Answer 3

electrons

Question 4

how far apart do two objects need to be for a electron microscope to distinguish between them?

Answer 4

1nm

Question 5

whats the magnification equation?

Answer 5

magnification + size of image/ size of real object

Question 6

whats 1mm in nm?

Answer 6

1,000,000nm

Question 7

whats the resolution or resolving power of a microscope?

Answer 7

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

Question 8

does increasing magnification and therefore increasing the size of the image increase resolution?

Answer 8

not always

Question 9

whats cell fractionation?

Answer 9

processes where cells are broken up and the different organelles they contain are separated out

Question 10

why is the solution used in cell fragmentation cold?

Answer 10

to reduce enzyme activity that might breakdown organelles.

Question 11

why is the solution used in cell fragmentation the same water potential as the tissue?

Answer 11

to prevent organelles bursting or shrinking as a result of osmotic gain or loss of water

Question 12

why is the solution used in cell fragmentation buffered?

Answer 12

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

Question 13

whats homogenation?

Answer 13

the first step in cell fragmentation when cells are broken up by a homogeniser (blender) releasing organelles from the cell. The resultant homogenate, is then filtered to remove any complete cells and large pieces of debris?

Question 14

whats ultracentrifugation?

Answer 14

the second step in cell fragmentation when the fragments filtered by the homogenate are separated in a centrifuge

Question 15

what does a cetrifuge do?

Answer 15

spins tubes of homogenate at a very high speed to create a centrifugal force

Question 16

whats the centrifugal process for animal cells?

Answer 16

-tube of filtrate is placed in the centrifuge and spun at a slow speed
- the heaviest organelles, the nuclei, are forced to the bottom of the tube, where they form a thin sediment or pellet
- the fluid at the top of the tube (supernatant) is removed leaving just the sediment
- the supernatant is then transferred into another tube and spun in the centrifuge faster the before
-the the next heaviest organelles, the mitochondria are forced to the bottom of the tube
-process is repeated at increasing speed for the rest of the organelles

Question 17

what speed of centrifugation is needed for nuclei to be separated out?

Answer 17

1000 revolutions min -1

Question 18

what speed of centrifugation is needed for mitochondria to be separated out?

Answer 18

3500 revolutions min-1

Question 19

what speed of centrifugation is needed for lysosomes to be separated out?

Answer 19

16500 revolutions min -1

Question 20

whats the advantages of an electron microscope?

Answer 20

• high resolving power due to short wavelength on electron beam
• electrons are negatively charged so beam can be focused using electromagnets

Question 21

in electron microscopes how do the stop electrons being absorbed or deflected by molecules in the air?

Answer 21

a near-vacuum is created

Question 22

how does a TEM work?

Answer 22

an electron beam passes through a thin section of the specimen. parts of the specimen absorbs electrons and appear dark other parts allow electrons to pass through so appear bright the image is produced of a screen and can be photographed to give a photomicrograph.

Question 23

why cant a TEM always reach its resolving power of 0.1nm?

Answer 23

• difficulties preparing the specimen limit the resolution that can be achieved
• a higher electron beam that is required may destroy the specimen

Question 24

what are the main limitations of the TEM and SEM?

Answer 24

-living specimens cannot be observed due to the vacuum
- complex staining process
-image may contain artefacts

Question 25

can the TEM produce 3D images?

Answer 25

no an extremely thin specimen is required so the image produced is 2D to create a 3D image with a series of photomicrographs however this is slow and complicated

Question 26

how does the SEM work?

Answer 26

the electron beam is passed back and forth across a portion of the specimen in a regular pattern. The electrons are scattered by the specimen which depends on the contours of the specimen surface allowing a 3D image to be built

Question 27

whats the resolving power of the basic SEM?

Answer 27

20nm