AQA A-Level Biology Paper 1 Exam Questions and Answers, Exams of Advanced Education

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AQA A-LEVEL BIOLOGY PAPER 1 EXAM

QUESTIONS

Describe the role of a ribosome in the production of a polypeptide. /3 - -1. mRNA binds to ribosome;

2. Idea of TWO codons/binding sites;
3. tRNA with ANTICODONS binds;
4. (Catalyses) formation of PEPTIDE bond between AMINO ACIDS (held by tRNA molecules);
5. Moves along (mRNA to the next codon); Describe the structure of glycogen. /2 - -1. Polysaccharide of α-glucose; OR polymer of α-glucose;
6. (Joined by) glycosidic bonds OR Branched structure; 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 NHE does this. /3 - -1. Co-transport;
7. Uses (hydrolysis of) ATP;
8. Sodium ion and proton bind to the protein;
9. Protein changes shape (to move sodium ion

and/or proton across the membrane); Explain the curves for max protease activity over time at 50C and 60C. /4 - -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; Describe the action of these membrane-bound dipeptidases and explain their importance. /2 - -1. Hydrolyse (peptide bonds) to release amino acids;
5. Amino acids can cross (cell) membrane; OR Dipeptides cannot cross (cell) membrane; OR Maintain concentration gradient of amino acids for absorption; Explain why the scientists suggested that patients should be treated with both the current antibiotic and the new one. Use information from Figure 2 (old antibiotic decreases number of bacteria, new one decreases it more) and your knowledge of evolution of antibiotic resistance in bacteria in your answer. /3 - -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;
6. Resistant bacteria will reproduce to produce (more) resistant bacteria;
7. (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; When measuring the leakiness of herbicide-treated cell membranes to ions, why did the scientists gently shake the flasks containing the leaf discs? /1 - - (Shaking) So all surfaces of the leaf discs are exposed (to water)/so all submerged; OR To maintain diffusion/concentration gradient (for ions out of leaf discs); 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 rheumatoid arthritis? /2 - -1. The antibody against virus (antigen) will bind to collagen;

2. This results in the destruction of the (human) cells/collagen; Explain six ways in which an insect's tracheal system is adapted for efficient gas exchange. /3 - -1. Tracheoles have thin walls so short diffusion distance to cells;
3. Highly branched/large number of tracheoles so short diffusion distance to cells;
4. 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);
5. Fluid in the end of the tracheoles that moves out (into tissues) during exercise so faster diffusion through the air to the gas exchange surface; OR Fluid in the end of the tracheoles that moves out (into tissues) during exercise so larger surface area (for gas exchange);
6. Body can be moved (by muscles) to move air so maintains diffusion/concentration gradient for oxygen/carbon dioxide; The damselfly larva is a carnivore that actively hunts prey. It has gills to obtain oxygen from water. Some other species of insect have larvae that are a similar size and shape to damselfly larvae and also live in water. These larvae do not actively hunt prey and do not have gills. Explain how the presence of gills adapts the damselfly to its way of life. /2 - -1. Damselfly larvae has high(er) metabolic/respiratory (rate);
7. (So) uses more oxygen (per unit time/per unit mass); (ignore uptakes more oxygen) How do you calculate % uncertainty in area? - -% uncertainty in length + % uncertainty in width

Suggest how the student could improve the quality of her scientific drawing. /

• -1. Don't use shading;

2. Only use single lines/don't use sketching (lines)/ensure lines are continuous/connected;
3. Add further labels/annotations;
4. Don't cross label lines;
5. Add magnification/scale (bar); How large should a sample be? - -Large enough to be representative of the population What type of molecule is (hexadecanoic acid)? /2 - -saturated fatty acid No organelles are visible in the cytoplasm of this red blood cell. Suggest why. [ mark] - -Cytoplasm of red blood cell filled with haemoglobin; Before the cell was examined using the electron microscope, it was stained. This stain caused parts of the structure of the cell-surface membrane to appear as two dark lines. Suggest an explanation for the appearance of the cell-surface membrane as two dark lines. [3 marks] - -1.Membrane has phospholipid bilayer; 2.Stain binds to phosphate/glycerol; 3.On inside and outside of membrane;

Describe how substances move across cell-surface membranes by facilitated diffusion. [3 marks] - -1. Carrier/channel protein; 2.(Protein) specific/complementary to substance; 3.Substance moves down concentration gradient; Give an advantage of asexual and sexual reproduction. /2 - -Asexual has fewer stages so quicker OR Only one parent involved so can colonise new environment OR Produces clone so successful (geno/pheno)type maintained; Sexual increases genetic diversity so greater chance of survival/success; Explain why the maximum initial reaction rate (reached at high substrate concentrations) is higher with competitive inhibitors than with non- competitive. /4 - -1. CI binds to active sites of enzyme but NCI away from active site;

2. (Binding of) CI does not cause change in shape of active site but NCI does;
3. So with CI, at high substrate concentrations (active) enzyme still available but with NCI (active) enzymes no longer available;
4. At higher substrate concs likelihood of enzyme-substrate collisions increases with CI but this is not possible with NCI; Give two reasons why grassy strips with a variety of plant species increase the biodiversity of animals. [2 marks] - -1. Increase in plant diversity leads to more TYPES of food for animals; 2.Increase in variety of animals leads to increase in predator species;

3.Increase in niche/habitat; The scientists decided to collect animals, sorting the soil samples by hand, for 40 minutes. Suggest how the scientists decided that 40 minutes was an appropriate time. [2 marks] - -1. Repeat soil sorting for different times and record number of species collected;

2. Find optimum time / time beyond which further sorting does not lead to increase in animal species found; Do you agree that these results are significant? /1 (priniciple of 2 × SD) - -1. Overlap of 2 × SD shows probability of differences (in means) being due to chance is greater than 0.95; What was the range in the number of copies of the AMY1 gene? /1 - -2 to 11 Explain why the standard deviation for the mean (4.4) is ±2.0. /1 - -Data show great variation (around mean) OR 4.4 ± 2 × SD includes most of the values measured; The scientists calculated a correlation coefficient, R, from their data. They found R = 0.50, with P <0.0001. Explain the meaning of the result of their calculations. [3 marks] - -1. Shows a positive correlation;
3. There probability of getting this correlation by

chance is less than 0.0001;

3. Correlation is highly significant; The number of copies of the AMY1 gene, coding for salivary amylase, is unlikely to affect people's ability to digest starch. Explain why. [3 marks] - -1. Little digestion of starch by salivary amylase OR starch in mouth for a short period OR salivary amylase inactivated by stomach acid;
4. Amylase also secreted by pancreas;
5. So (most) starch digestion occurs in small intestine; Explain how the organic bases help to stabilise the structure of DNA. [2 marks]

• -1. Hydrogen bonds between the base pairs holds two strands together;

2. Many hydrogen bonds provides strength; Suggest one advantage of showing the genetic code as base sequences on mRNA, rather than triplets on DNA. [1 mark] - -ribosomes assemble polypeptides using mRNA code OR DNA has two strands each with a different (complementary) base sequence; Suggest the role of the mRNA stop codons. /2 - -1. Stop translation;
3. Result in detachment of polypeptide chain from ribosome;

Give the formula for calculating the percentage saturation of haemoglobin with oxygen. [1 mark] - -oxygenated haemoglobin ÷ maximum saturation × 100 The first molecule of oxygen to bind causes a change in the shape of the haemoglobin molecule. This change of shape makes it easier for other oxygen molecules to bind to the haemoglobin molecule. Explain how the haemoglobin saturation graph provides evidence for this. [2 marks] - -1. At low partial pressure of oxygen, little increase in saturation as oxygen increases;

2. (then) rapid rise as it gets easier for oxygen to bind; Suggest how the scientists could adapt their method to determine which tissue carried the radioactively labelled sucrose. [2 marks] - -1. Take thin (horizontal) sections of plant tissue/stem;
3. Place against photographic film in dark for several hours / carry out autoradiography; The scientists dried the plant samples in an oven at 100 °C. Give two reasons why they used this temperature. [2 marks] - -1. Evaporates all water
4. (But) does not burn (organic compounds); Since the year 2000, strains of Neisseria meningitidis that are resistant to penicillin, sulfonamides and rifampin have been discovered in the UK. Describe how a population of Neisseria meningitidis (Nm) can become resistant to these antibiotics.

[4 marks] - -1. Mutation;

2. Results in Nm cell with allele for resistance to one antibiotic/to named antibiotic;
3. (This) cell survives and passes the allele for resistance to offspring;
4. Process repeated with different genes conferring resistance to each of the other (two) antibiotics; Explain two ways in which the structure of fish gills is adapted for efficient gas exchange. [2 marks] - -1. Many lamellae/filaments so large surface area;
5. Thin (surface) so short diffusion pathway; Cells lining the ileum of mammals absorb the monosaccharide glucose by co- transport with sodium ions. Explain how. [3 marks] - -1. Sodium ions actively transported from ileum cell to blood;
6. Maintains/forms diffusion gradient for sodium to enter cells from gut (and with it, glucose);
7. Glucose enters by facilitated diffusion with sodium ions; A student puts amylase and starch inside of Visking tubing in a beaker of water. She then tests the solution in the beaker with Biuret's, Benedict's and potassium iodide. Explain the results. /3 - -1. Biuret: protein molecules too large to pass through tubing; (not enzyme)
8. Iodine in potassium iodide solution: starch molecules too large to pass through tubing;

3. Benedict's: starch hydrolysed to maltose, which is able to pass through tubing (amylase doesn't hydrolyse to glucose) Explain the differences between the mean concentrations of antibodies in blood before vaccination, after 1st dose of vaccine and after 2nd dose of vaccine. /4 - -1. Before vaccination no antibody released because patients not yet encountered antigen;
4. (primary response/after first dose) activation/clonal selection of B cells into plasma cells;
5. Plasma cells release antibodies;
6. (secondary response/after second dose) memory cells produce more antibodies/produce antibodies more quickly; A student concluded from a graph of the data in Table 5 that the bacterium lives at 15 °C, which is the optimum temperature for enzyme activity. Do the data support the student's conclusion? [4 marks] - -Yes:
7. Expect optimum temperature of enzyme to be same/similar to temperature where bacterium lives;
8. Optimum temperature for enzyme (appears to be around) 15 °C; No:

3. Need data from more temperatures (between 10 °C and 20 °C);
4. Data for only isolated enzyme OR Isolation may affect activity; Each phloem-sap-feeding insect receives a few gut bacteria from its parent. Suggest how this has caused a reduction in genetic diversity of the bacteria. [ marks] - -1. (Only few bacteria passed from parent, so) only a few (copies of) genes passed on (in bacteria);
5. May not/does not include all alleles (of genes, so diversity reduced) OR Small number of bacteria transmitted means unrepresentative sample; A scientist found that leaf-chewers and xylem-sap-feeders had a greater effect on plant growth than phloem-sap-feeders (greater reduction in leaf area). Other than environmental factors, give two features the scientist would have controlled in his experiment to ensure this conclusion was valid. [2 marks] - -1. Number/mass/density of insects per plant;
6. Stage of development/size of plants/insects;