microscopy

Question 1

light microscopes

Answer 1

use light to form an image
* observe live specimens
* produce colour image

Question 2

electron microscopes

Answer 2

use electrons to form an image

Question 3

how does TEM work

Answer 3

• electromagnets to focus a beam of electrons
• This beam of electrons is transmitted through the specimen
• Denser parts of the specimen absorb more electrons so they appear darker on the image

Question 4

ADV of TEM

Answer 4

• provide high-resolution images
• allows the internal structures to be seen

Question 5

DISADV of TEM

Answer 5

• only be used with very thin specimens
• cannot be used to observe live specimens
• do not produce a colour image

Question 6

how does SEM work

Answer 6

• SEMs scan a beam of electrons across the specimen
  -This beam bounces off the surface of the specimen and the electrons are detected
• forming an image

Question 7

ADV of SEM

Answer 7

• can be used on thick or 3-D specimens
• They allow 3-D structure of specimens to be observed

Question 8

DISADV of SEM

Answer 8

• lower resolution images
• They cannot be used to observe live specimens
• They do not produce a colour image

Question 9

what is the purpose of cell fractionation

Answer 9

to break up cells and separate organelles

Question 10

what do you do before cf

Answer 10

tissue placed in cold, isotonic buffer solution

Question 11

why is a homogeniser used

Answer 11

to break the plasma membrane of the cells and releases the organelles into a solution called the homogenate

Question 12

why is the homogenate filtered

Answer 12

to remove large cellular debris

Question 13

steps of ultracentrifugation

Answer 13

• filtrate is first spun at a low speed
• largest, heaviest organelles to settle at the bottom of the tube, they form a pellet
• rest of the organelles stay suspended in the solution above the pellet ( the supernatant)
• The supernatant is drained off and placed into another tube, is spun at a higher speed forms another supernatant
• new supernatant is drained off and placed into another tube, is spun at an even higher speed
• process repeated

Question 14

cf and ultracentrifugation

Answer 14

Break open tissue and filter
In ice cold, isotonic, buffered
Centrifuge and remove cellular debris
Centrifuge at high(er) speed,

Question 15

heaviest to lightest organelles

Answer 15

Nuclei
Chloroplasts (if carrying out cell fractionation of plant tissue)
Mitochondria
Lysosomes
Endoplasmic reticulum
Ribosomes