paper 2

Question 1

Explain how a resting potential is maintained across the axon membrane in a
neurone.

Answer 1

1. Higher concentration of potassium ions inside
   and higher concentration of sodium ions outside
   (the neurone)
   OR
   potassium ions diffuse out
   OR
   sodium ions diffuse in;
2. (Membrane) more permeable to potassium ions
   (leaving than sodium ions entering)
   OR
   (Membrane) less permeable to sodium ions
   (entering than potassium ions leaving);
3. Sodium ions (actively) transported out and
   potassium ions in;

Question 2

Describe and explain how the polymerase chain reaction (PCR) is used to amplify a
DNA fragment

Answer 2

1. (Requires DNA fragment) DNA polymerase,
   (DNA) nucleotides and primers;
2. Heat to 95 °C to break hydrogen bonds (and
   separate strands);
3. Reduce temperature so primers bind to
   DNA/strands;
4. Increase temperature, DNA polymerase joins
   nucleotides (and repeat method);

Question 3

describe shape of curve for pcr

Answer 3

1. (Initially) number (of molecules) doubling is low
   OR
   Doubles each cycle to produce exponential
   increase;
2. Plateaus as no more nucleotides/primers;