paper 3

Question 1

Suggest why the percentage change in tumour volume is recorded when investigating the growth of lung tumours

Answer 1

Percentage change - To allow comparison as tumours may differ in volume/size (at the start of the investigation)

Tumour volume - tumours may differ in length/width/shape

Question 2

What does the log scale on a graph show about the data?

Answer 2

Shows big range in the dependant variable

Question 3

The rate of movement through a shoot in a potometer may not be the same as the rate of water movement through the shoot of a whole plant. Suggest why.

Answer 3

Plant has roots
OR
xylem cells very narrow;

Question 4

NOTCH1 = leads to production of transcription factor associated with CD20
CD20 = protein on surface of B cells that rituximab binds to.

Suggest how mutation of NOTCH1 led to a difference in percentage of B cells destroyed.

Answer 4

1. Mutation changes the tertiary structure / amino acid sequence of transcription factor;
2. Transcription factor not complementary to / cannot bind to CD20 gene / CD20 DNA;
3. Little / less / not enough / no mRNA for CD20
   produced
   OR
   Little / less / not enough / no (mRNA for) CD20
   translated / produced;
4. (Not enough CD20 so) nothing / little for
   Rituximab to bind to, so few / no B cells
   destroyed;

Question 5

Binding of one molecule of oxygen to haemoglobin makes it easier for a second molecule of oxygen to bind. Explain why.

Answer 5

1. Binding of first oxygen changes quaternary (structure) of haemoglobin;
2. Creates / leads to / uncovers second / another
   binding site
   OR
   Uncovers another iron / Fe / haem group to
   bind to;

Question 5

Scientists for investigation of bacteria set up cultures in sterile glass bottles.

Suggest one suitable method for sterilising the bottles and explain why it was necessary to sterilise them.

Answer 5

1. eg in boiling water / steam / wash in
   disinfectant / wash in alcohol
2. (Reason) to remove / kill other bacteria /
   organisms that might break down ammonia
   or other bacteria compete with / kill bacteria that
   produce amoA

Question 6

Describe the role of saprobionts in the nitrogen cycle.

Answer 6

1. They use enzymes to decompose proteins/DNA/RNA/urea;
2. Producing/releasing ammonium ions;

Question 7

Describe how you would obtain a quantitative measure of the cloudiness in 3 samples of water from 3 different rivers.

Answer 7

1. Use of colorimeter;
2. Measure the absorbance/transmission (of light);
3. Example of how method can be standardised eg: same volume of water, zeroing colorimeter, same wavelength of light, shaking the sample;

Question 7

Explain why an increase in thickness of medulla causes an increase in the concentration of urine.

Answer 7

1. Thicker medulla means longer loop of Henle
2. Means increase in sodium ion concentration (in medulla)
   OR
   Means sodium ion gradient maintained for longer (in medulla)
   OR
   Means more sodium ions are moved out (into medulla);
3. Water potential gradient maintained for longer so more water reabsorbed from loop and collecting duct by osmosis

Question 8

Name one type of gene mutation and explain how this mutation could lead to production of a shorter polypeptide. (2)

Answer 8

(1 and 2)
1. Deletion/translocation;
2. Could mean triplet(s)/codon(s) missing
OR
Could mean amino acid(s) missing (from the
polypeptide/SURF1);

(3 and 4)
3. Substitution/inversion/addition/duplication/
deletion/translocation;
4. Could result in a (premature) stop triplet/codon;

Question 9

The frequency of a recessive, inherited condition is higher in the Faroe Islands (isolated islands) than globally.

Suggest and explain one reason why.

Answer 9

(MARK IN PAIRS 1+2 OR 3+4)

1. Genetic drift;
2. Frequency is higher by chance
   OR
   High frequency is not due to natural selection;
3. (Only) inbreeding/interbreeding (within a
   population)
   OR
   No (inter)breeding with other populations
   OR
   (Inherited from) common ancestor;
4. Low genetic diversity
   OR
   Small gene pool
   OR
   Little gene flow
   OR
   Higher chance of inheriting allele
   OR
   Frequency of allele higher (in offspring);

Question 10

Define population

Answer 10

1. A group of organisms of the same species in a particular space at a particular time;
2. That can potentially interbreed;

Question 11

Why might it not be possible to extrapolate data?

Answer 11

Not a linear relationship

Question 12

Suggest and explain reasons why use of induced pluripotent stem cells could have advantages over the use of gene therapy (to correct red-green colour blindness)

Answer 12

1. (Use of iPS cells) long-term;
   Accept ‘gene therapy short-term’ or ‘only two years’
   Accept ‘permanent’
2. (Use of iPS cells) less chance of rejection/immune response;
3. (Use of iPS cells) single treatment;
   Accept ‘gene therapy ‘regular/frequent treatment’’
4. Harm/side effects from using viruses (in gene therapy);

Question 13

After the student had stared at a purple square, he saw a green afterimage.
Suggest why.

Answer 13

1. (When staring at purple) red sensitive and blue sensitive cones are stimulated / green sensitive cones are not stimulated;
2. Red and blue cone cells become exhausted / stop working;
3. (Afterimage due to) green sensitive cone cells working;