3.1 Methods of studying cells

Question 1

What is cell fractionation

Answer 1

The process by which cells are broken up and the different organelles they contain are separated out

Question 2

What are the conditions that must occur before cell fractionation can begin

Answer 2

1. Cold - prevent enzyme activity that may break down the organelles
2. Isotonic - prevent bursting or shrinking of cells as a result of osmotic loss/gain
3. Buffered - keep pH constant. Any pH change may alter the structure of organalles

Question 3

What are the two stages of cell fractionation

Answer 3

1. Homogenation - physical breaking up of cells

2. Ultracentrifugation - Fragments are filtered

Question 4

What is the process of homogenation

Answer 4

Cells are broken up in a homogeniser, this releases organelles from inside the cell. The resultant fluid, called homogenate, is filtered to remove debris

Question 5

What is the process of ultracentrifugation

Answer 5

1. The tube of filtrate is placed in the centrifuge and spun at a slow speed
2. The heaviest organelles, the nuclei, are forced to the bottom of the tube where they form a thin sediment
3. The fluid at the top of the tube (supernatant) is removed, leaving just the nuclei sediment
4. The supernatant is transferred into another tube and spun at a faster speed than before.
5. The next heaviest organelle is the mitrochondria, which are forced to the bottom of the tube
6. The process is repeated and the third heaviest organelle are lysosomes

Question 6

What is the weighting of organelles (heaviest to lightesT)

Answer 6

1. Nuclei - 1,000 revs
2. Mitochondria - 3,500 revs
3. Lysosomes - 16,500 revs

Question 7

Describe how you could make a temporary mount of a piece of plant tissue to observe the position of starch grains when using a light microscope

Answer 7

1. Add a drop of water to a glass slide
2. Obtain a thin section of plant tissue
3. Stain the tissue with iodine
4. Lower cover slip with a mounted needle