2016 AS Paper 1

Question 1

Describe how the complementary strand of HIV DNA is made

Answer 1

1.Complementary nucleotides/bases pair

2. DNA polymerase;
3. Nucleotides join together (to form new strand)/phosphodiester bonds form

Question 2

Contrast the structures of DNA and mRNA molecules to give three differences

Answer 2

1.DNA double stranded/double helix and mRNA single-stranded;

2.DNA (very) long and RNA short;

3. Thymine/T in DNA and uracil/U in RNA;
4. Deoxyribose in DNA and ribose in RNA;
5. DNA has base pairing and mRNA doesn’t/DNA has hydrogen bonding and mRNA doesn’t;
6. DNA has introns/non-coding sequences and mRNA doesn’t

Question 3

Describe how you would test for the presence of a lipid in a sample of food.

Answer 3

1. Add ethanol, then add water;
2. White (emulsion shows lipid);

Question 4

This fat substitute cannot be digested in the gut by lipase.

Suggest why.

Answer 4

1. (Fat substitute) is a different/wrong shape/not complementary;
   OR
   Bond between glycerol/fatty acid
   and propylene glycol different (to
   that between glycerol and fatty
   acid)/no ester bond;
2. Unable to fit/bind to (active site of)
   lipase/no ES complex formed;

Question 5

Describe how ATP is resynthesised in cells.

Answer 5

1. From ADP and phosphate;
2. By ATP synthase;
3. During respiration/photosynthesis;

Question 6

Give two ways in which the hydrolysis of ATP is used in cells

Answer 6

1. To provide energy for other
   reactions/named process;
2. To add phosphate to other
   substances and make them more
   reactive/change their shape;

Question 7

Y is a protein. One function of Y is to transport cellulose molecules across the
phospholipid bilayer.

Using information from Figure 3, describe the other function of Y.

Answer 7

1. (Y is) an enzyme/has active
   site/forms ES complex;
2. That makes cellulose/attaches
   substrate to cellulose/joins β
   glucose;
   OR
3. Makes cellulose/forms glycosidic
   bonds;
4. From β glucose;

Question 8

Describe the induced-fit model of enzyme action.

Answer 8

1. (before reaction) active site not
   complementary to/does not fit
   substrate;
2. Shape of active site changes as
   substrate binds/as enzyme-substrate complex forms;
3. Stressing/distorting/bending bonds
   (in substrate leading to reaction);

Question 9

The scientist used quantitative Benedict’s tests to produce a calibration curve of
colorimeter reading against concentration of maltose.

Describe how the scientist would have produced the calibration curve and used
it to obtain the results in Figure 4.

Do not include details of how to perform a Benedict’s test in your answer

Answer 9

1. Make/use maltose solutions of
   known/different concentrations
   (and carry out quantitative
   Benedict’s test on each);
2. (Use colorimeter to) measure
   colour/colorimeter value of each
   solution and plot calibration
   curve/graph described;
3. Find concentration of sample from
   calibration curve;

Question 10

Human papilloma virus (HPV) is the main cause of cervical cancer. A vaccine has been developed to protect girls and women from HPV.

Describe how giving this vaccine leads to production of antibody against HPV.

Answer 10

1. Vaccine/it contains antigen (from
   HPV);
2. Displayed on antigen-presenting cells;
3. Specific helper T cell (detects antigen and) stimulates specific B cell;
4. B cell divides/goes through
   mitosis/forms clone to give plasma
   cells;
5. B cell/plasma cell produces antibody;

Question 11

3 The doctors carried out a statistical test to determine whether the antibody
concentrations were significantly different in girls given two doses of the vaccine, compared with those given three doses. They determined the mean
concentrations of antibody 9 months after the first dose of vaccine.

What statistical test should the doctors have used? Give the reason for your
choice.

Answer 11

t-test, because comparing two means;

Question 12

Give two ways doctors could use base sequences to compare different types of
HPV.

Answer 12

1. Compare (base sequences of) DNA;
2. Look for mutations/named mutations (that change the base sequence);
3. Compare (base sequences of)
   (m)RNA;

Question 13

Suggest why the development of a monopolar mitotic spindle would prevent successful mitosis.

Answer 13

1. No separation of chromatids/chromosomes/centromeres;
2. Chromatids/chromosomes all go to one pole/end/sides of cell/not pulled to
   opposite poles;
3. Doubles chromosome number in
   cell/one daughter cell gets no
   chromosomes or chromatids;