BIO 2017

Question 1

Describe the role of a ribosome in the production of a polypeptide. Do not include
transcription in your answer

Answer 1

1. mRNA binds to ribosome;
2. Idea of two codons/binding sites;
3. (Allows) tRNA with anticodons to bind/associate;
4. (Catalyses) formation of peptide bond between
   amino acids (held by tRNA molecules);
5. Moves along (mRNA to the next
   codon)/translocation described;

Question 2

Sodium ions from salt (sodium chloride) are absorbed by cells lining the gut. Some
of these cells have membranes with a carrier protein called NHE3.
NHE3 actively transports one sodium ion into the cell in exchange for one proton
(hydrogen ion) out of the cell.
Use your knowledge of transport across cell membranes to suggest how NHE3
does this.

Answer 2

1. Co-transport;
2. Uses (hydrolysis of) ATP;
3. Sodium ion and proton bind to the protein;
4. Protein changes shape (to move sodium ion
   and/or proton across the membrane);

Question 3

Explain the shape of the curves at 50 °C and 60 °C.

Answer 3

1. Both denatured (by high temperature);
2. Denaturation faster at 60 °C due to more
   (kinetic) energy;
3. Breaks hydrogen/ionic bonds (between amino
   acids/R groups);
4. Change in shape of the active site/active site no
   longer complementary so fewer enzyme-
   substrate complexes formed/substrate does not
   fit;

Question 4

Suggest one advantage to a bacterium of secreting an extracellular protease in its
natural environment.

Answer 4

To digest protein;
2. (So) they can absorb amino acids for
growth/reproduction/protein synthesis/synthesis
of named cell component;
OR
(So) they can destroy a toxic substance/protein;

Question 5

Mammals have some cells that produce extracellular proteases. They also have
cells with membrane-bound dipeptidases.
Describe the action of these membrane-bound dipeptidases and explain their
importance.

Answer 5

1. Hydrolyse (peptide bonds) to release amino
   acids;
2. Amino acids can cross (cell) membrane;

Question 6

The scientists suggested that people newly diagnosed with this bladder infection
should be treated with both the current antibiotic and the new antibiotic.
Explain why the scientists made this suggestion.

Answer 6

1. (From Fig 2) New/old antibiotic does not kill
   all bacteria;
   OR
   (From Fig 2) Some bacteria are resistant to
   the new/old antibiotic;
2. Resistant bacteria will reproduce to produce
   (more) resistant bacteria;
3. (Use of both) one antibiotic will kill bacteria
   resistant to the other antibiotic;
   OR
   Unlikely that bacteria are resistant to both the
   new and the old antibiotic;
   OR
   Use of both antibiotics (likely to) kill all/most
   bacteria;

Question 7

Describe how presentation of a virus antigen leads to the secretion of an antibody
against this virus antigen.

Answer 7

. Helper T cell/TH cell binds to the antigen (on
the antigen-presenting cell/phagocyte);
2. This helper T/TH cell stimulates a specific B
cell;
3. B cell clones

Question 8

Collagen is a protein produced by cells in joints, such as the knee.
Rheumatoid arthritis (RA) is an auto-immune disease. In an auto-immune disease,
a person’s immune system attacks their own cells. RA causes pain, swelling and
stiffness in the joints.
Scientists have found a virus that produces a protein very similar to human
collagen.
Suggest how the immune response to this viral protein can result in the
development of RA.

Answer 8

The antibody against virus (antigen) will bind
to collagen;
2. This results in the destruction of the (human)
cells/collagen;

Question 9

The antibody against virus (antigen) will bind
to collagen;
2. This results in the destruction of the (human)
cells/collagen;

Answer 9

1. The (base) sequence of DNA;
2. The (base) sequence of mRNA;
3. The amino acid sequence (of proteins);

Question 10

Explain three ways in which an insect’s tracheal system is adapted for efficient gas
exchange

Answer 10

1. Tracheoles have thin walls so short
   diffusion distance to cells;
2. Highly branched/large number of
   tracheoles so short diffusion distance to
   cells;
3. Highly branched/large number of
   tracheoles so large surface area (for gas
   exchange);
4. Tracheae provide tubes full of air so fast
   diffusion (into insect tissues);

Question 11

Explain how the presence of gills adapts the damselfly to its way of life.

Answer 11

1. Damselfly larvae has high(er)
   metabolic/respiratory (rate);
2. (So) uses more oxygen (per unit time/per
   unit mass

Question 12

An environmental scientist investigated a possible relationship between air
pollution and the size of seeds produced by one species of tree.
He was provided with a very large number of seeds collected from a population of
trees in the centre of a city and also a very large number of seeds collected from a
population of trees in the countryside.
Describe how he should collect and process data from these seeds to investigate
whether there is a difference in seed size between these two populations of trees.

Answer 12

1. Use random sample of seeds (from each
   population);
2. Use (large enough) sample to be representative
   of whole population;
3. Indication of what size was measured eg mass;
4. Calculate a mean and standard deviation (for
   each population);
5. Use the (Student’s) t-test;
6. Analyse whether there is a significant difference
   between (the means of) the two populations;