Methods of studying cells

Question 1

What type of lens can act as a magnifying glass?

Answer 1

A simple convex glass lens.

Question 2

How can we get lenses to work more effectively?

Answer 2

By using them in pairs in a compound light microscope.

Question 3

What is limiting about using light?

Answer 3

Light has a relatively long wavelength and so can only distinguish between two objects if they are more than a certain distance apart (0.2micrometres).

Question 4

What can we use in a microscope instead of rays of light?

Answer 4

Electrons, as they have shorter wavelengths. They can distinguish from objects 0.1micrometres apart.

Question 5

What are the object and image?

Answer 5

The material that is put under a microscope is referred to as the object. The appearance of this material when viewed under the microscope is referred to as the image.

Question 6

How do you calculate magnification?

Answer 6

size of image / size of real image.

Question 7

How do you calculate the size of real object?

Answer 7

Size of image / magnification.

Question 8

What is the resolution?

Answer 8

The minimum distance apart that two objects can be in order for them to appear at separate items. Greater resolution means greater clarity.

Question 9

What does the resolving power of a microscope depend on?

Answer 9

The wavelength or form of radiation used.

Question 10

What is the limit of resolution?

Answer 10

Up to this point increasing the magnification will reveal more detail but beyond this point increasing the magnification will not do this.

Question 11

What is cell fractionation?

Answer 11

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

Question 12

Before cell fractionation can begin what must be done?

Answer 12

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

Question 13

Describe the solution used in cell fractionation and explain why it has these properties.

Answer 13

Cold- to reduce enzyme activity that might break down the organelles
Same water potential as the tissue- to prevent organelles bursting or shrinking as a result of osmotic gain or loss of water
Buffered- so that the pH doesn’t fluctuate. Any change in pH could alter the structure of the organelles or affect the functioning of enzymes.

Question 14

What are the two stages of cell fractionation called?

Answer 14

Homogenation and ultracentrifugation.

Question 15

What happens in homogenation?

Answer 15

Cells are broken up by a homogeniser (blender). This releases the organelles from the cell. The resultant fluid, known as homogenate, is then filtered to remove any complete cells and large pieces of debris.

Question 16

What is ultracentrifugation?

Answer 16

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

Question 17

Describe the process of ultracentrifugation for animal cells.

Answer 17

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 or pellet.
3) The fluid at the top of the tube (supernatant) is removed, leaving just the sediment of the nuclei.
4) The supernatant is transferred to another tube and spun in the centrifuge at a faster speed than before.
5) The next heaviest organelles, mitochondria are forced to the bottom.
6) The process of the heaviest organelle being sedimented and separated out is continued until all are separate.

Question 18

What developments have ultracentrifugation and homogenation allowed in science?

Answer 18

They allowed a detailed study of the structure and function of organelles, by showing what isolated components can do.