SB5f

Question 1

What is the structure of viruses?

Answer 1

1. Contain DNA/RNA
2. May have outer lipid envelope
3. Have protein coat/capsid made up of repeating capsomeres
4. Some contain the enzyme reverse transcriptase

Question 2

What is the process of the lytic cycle?

Answer 2

1. Bacteriophage (type of virus) attaches on host cell
2. Releases its DNA into the host cell
3. Host’s DNA breaks down
4. The virus uses all the processes in the cell to produce proteins, lipids, carbohydrates, and DNA (all the parts needed to make a new virus)
5. The new viruses are assembled and break the cell - destroying it - then leave to go infect other cells

Check SB5f diagram (booklet).

Question 3

What is the process of the lysogenic cycle?

Answer 3

1. Bacteriophage (type of virus) attaches on host cell
2. Releases its DNA into the host cell
3. The DNA gets incorporated into the DNA of the host cell
4. The virus remains dormant
5. As the cell multiplies to form new cells, the new cells also contain the DNA of the virus
6. Once something triggers the virus, its DNA becomes active and enters the lytic cycle

Check SB5f diagram (booklet).

Question 4

How do we make a bacteria lawn plate and test different chemicals, bacteria or viruses?

Answer 4

1. Add the bacteria in the liquid gel
2. Stir it, then put it in the petri dish to let it cool down
3. Add the bacteria in the solid agar gel using an inoculating loop
   4.

Check SB5f drawing (booklet).

Question 5

How do we test which viruses attack bacteria?

Answer 5

1. Take a petri dish and inoculate the nutrient agar with bacteria
2. Create wells or use paper disks to add the viruses (can also use chemicals/antibiotics)
3. Viruses will diffuse through the agar
4. Incubate the petri dishes at 25°C for 3-7 days
5. Check for a clear zone around the paper disks/well
6. Clear zones show bacteria have died
7. The bigger the clear zone, the more effective the virus is
8. Calculate the area of the clear zone using πr^2

Question 6

What aseptic techniques are used when performing experiments on bacteria?

Answer 6

1. Sterilising inoculating loop with Bunsen burner flame
2. Sterilising agar and equipment with an autoclave
3. Keeping lids of petri dishes closed after bacterial growth
4. Use of antiseptics to clean area of work
5. Tape cross-wise the petri dish to avoid growth of anaerobic bacteria

Question 7

Why are aseptic techniques used?

Answer 7

1. Bunsen burner flame kills all microorganisms on the loop
2. Loop is needed to be sterilised so that unwanted microorganisms are killed
3. No competition of resources and space in the agar - only desired bacteria can grow

Question 8

What are some controlled variables in experiments on bacteria?

Answer 8

1. Concentration of antiseptic/antibiotic
2. Volume of antiseptic/antibiotic
3. Same type of agar
4. Volume of bacteria
5. Incubation temperature
6. Growth period