2. Cells - Methods Of Studying Cells And Microscopy

Question 1

What is the equation for magnification?

Answer 1

Magnification = size of image/size of real object

Question 2

What is resolution?

Answer 2

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

Question 3

Briefly explain what the process of cell fractionation is:

Answer 3

It is the process where cells are broken up and the different organelles they contain are separated out.

Question 4

What happens before cell fractionation can begin?

Answer 4

The tissue is placed in a cold, buffered solution of the same water potential as the tissue.

Question 5

For cell fractionation, why is this solution cold?

Answer 5

To reduce enzyme activity that might break down the organelles.

Question 6

For cell fractionation, why is this solution buffered?

Answer 6

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

Question 7

For cell fractionation, why is this solution of the same water potential as the tissue?

Answer 7

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

Question 8

What are the two stages to cell fractionation?

Answer 8

-Homogenisation
-Ultracentrifugation

Question 9

What is the process of homogenisation?

Answer 9

Cells are broken up by a homogeniser (blender). This releases the organelles from the cell. The resultant fluid, known as the homogenate, is then filtered.

Question 10

Why is the homogenate filtered during homogenisation?

Answer 10

To remove any complete cells and large pieces of debris.

Question 11

What is the process of ultracentrifugation?

Answer 11

The fragments in the filtered homogenate are separated in a machine called a centrifuge. This spins the tubes of homogenate at very high speed in order to create a centrifugal force.

Question 12

What is the first stage of ultracentrifugation?

Answer 12

The tube of filtrate is placed in the centrifuge and spun at a low speed.

Question 13

What is the heaviest organelles are therefore is forced to the bottom of the tube first?

Answer 13

The nuclei

Question 14

What do the organelles form once forced to the bottom of the tube?

Answer 14

A thin sediment or pellet.

Question 15

What is the fluid at the top of the tube called after the sediment is removed?

Answer 15

The supernatant.

Question 16

What is changed with each spin on the centrifuge?

Answer 16

Speed - increases every time.

Question 17

What is the next heaviest organelles after the nuclei that are forced to the bottom of the tube once spin at higher speed?

Answer 17

The mitochondria.

Question 18

Compare how an optical microscope and transmission electron microscope work:

Answer 18

• Optical microscope uses light waves, a TEM uses a beam of electrons
• TEM focuses using magnets, optical uses glass lenses

Question 19

Contrast the limitations of the use of an optical microscope and a TEM:

Answer 19

• TEM has a greater resolution than an optical microscope
• So TEM can observe smaller organelles/in greater detail
• TEM can only view dead specimens but optical can view live specimens
• TEM does not show colour, optical does
• TEM requires very thin specimens
• Therefore TEM requires a more complex/time consuming preparation

Question 20

Briefly explain how to calibrate the eyepiece graticule:

Answer 20

• A special microscope slide, a stage micrometer, is required
• Line up the eye-piece graticule scale and the stage micrometer
• Calculate the length of divisions on the eye-piece graticule