Paper 3 Last Minute

Question 1

M. luteus is not resistant to chloramphenicol.

Suggest two reasons why the bacteria were able to grow in the culture containing chloramphenicol.

Answer 1

1. The concentration (of chloramphenicol) was too low/dilute (to kill all)
   OR
   There were too many M. luteus/bacteria for chloramphenicol/antibiotic to kill;

(Contamination with) other/resistant bacteria; Mutation (occurred);

Question 2

Suggest why the student soaked the root tips in hydrochloric acid in step 2.

Answer 2

1. To break down links between cells/cell walls
   OR
   To separate cells/cell walls
   OR
   To break down/hydrolyse cellulose/cell wall;
2. Allowing the stain to pass/diffuse into the cells
   OR
   Allowing the cells to be (more easily) squashed;
3. To stop mitosis;

Question 3

Pressing the coverslip downwards enabled the student to observe the stages of mitosis clearly.
Explain why.

Answer 3

To create a single/thin layer of cells
OR
To spread out cells;
2. So that light could pass through;

Question 4

Recombinant DNA technology can involve the transfer of fragments of human DNA into bacteria. The bacteria are then used to produce human proteins.

Give two reasons why bacteria are able to use human DNA to produce human
proteins.

Answer 4

genetic/DNA code is universal
OR
The same triplets/codons code for the same amino acids (in all species);
2. (The mechanism of) transcription is universal;
3. (The mechanism of) translation is universal;

Question 5

Enhancer