Cell structure

Question 1

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 use electrons and optical use light
2. TEM allows a greater resolution
3. So with TEM smaller organelles can be observed and in greater detail
4. TEM view only dead specimens and
   optical can view live specimens
5. TEM does not show colour and optical can
6. TEM requires thinner specimens
7. TEM requires a more complex and time consuming
   preparation;
8. TEM focuses using magnets and optical uses glass lenses

Question 2

How do viruses replicate?

Answer 2

1. Attachment proteins are complementary to receptors on cell surface membrane of target cell so bind/ attach.
2. Viral nucleic acid enters cell.
3. Nucleic acid replicated in cell, reverse transcriptase makes DNA for RNA.
4. Cell produces viral proteins.
5. New viruses assembled and released for cell/

Question 3

What happens in the interphase?

Answer 3

G1 - cell growth, protein synthesis and new organelles made.
S- DNA replication
G2 - more cell growth, DNA checked and new organelles made.

Question 4

Structure of a virus.

Answer 4

1. RNA
2. Reverse transcriptase
3. capsid
4. Phospholipid viral envelope
5. Attachment proteins;

Question 5

Why it is not possible to determine the identity of structures using an optical microscope?

Answer 5

1. Resolution too low;
2. Because wavelength of light is too long;

Question 6

How could you make a temporary mount of a piece of plant tissue to observe using an optical microscope.

Answer 6

1. Add drop of water to (glass) slide;
2. Obtain thin section of plant tissue and place on slide
3. Stain with iodine in potassium iodide.
4. Place/ lower cover slip slowly and carfeully to prevent air bubbles using a mounted needle.