Module 2 - Methods of studying cells

Question 1

6 marks

Contrast how an optical microscope and a transmission electron microscope work
and contrast the limitations of their use when studying cells.

Answer 1

1. TEM uses electrons and optical uses light
2. TEM allows a greater resolution
3. So with TEM smaller organelles can be observed e.g. ribosome
4. TEM view only dead specimens and optical can view live specimens
5. TEM requires thinner specimens
6. TEM requires a more complex/ time consuming preperation
7. TEM focuses using magnets and optical uses glass lenses

Question 2

2 marks

The scientists broke open the cells to produce a suspension of cell contents.
Describe how the scientists would remove large organelles from this suspension of cell contents.

Answer 2

1. Centrifuge at low speeds
2. Large/dense organelles removed in first pellet

Question 3

4 maarks

Describe how a sample of chloroplasts could be isolated from leaves

Answer 3

1. Break open cells/ homogenise and filter
2. In cold, isotonic, buffered solution
3. Centrifuge and remove nuclei (nucleus removed in first pellet, filter supernatant)
4. Centrifuge higher speed, chloroplasts settle out

Question 4

6 marks

Describe and explain how you would use cell fractionation and ultracentrifugation to obtain a sample of nuclei from muscle tissue.

Answer 4

1. Homogenise to break open cells
2. Filter to remove debris
3. Cold solution to prevent enzyme activity
4. Isotonic solution to prevent osmosis
5. Buffered solution to stop enzymes/protein denaturing
6. Centrifuge lower speed so nuclei in pellet/move to bottom