past paper questions

When siRNA binds to mRNA, name the complementary base pairs holding the siRNA and mRNA together. One of the bases is named for you. (1 mark)

cytosine with guanine adenine with uracil

Why is the genetic code described as being universal? (1 mark)

(In all organisms / DNA,) the same triplet codes for the same amino acid.

Describe what the results in the table show. (2 marks)

1. Large(r) percentage of resistant bacteria in turkeys; 2. Large(r) percentage of resistant bacteria in turkey farmers

The genetic code uses four different DNA bases. What is the maximum number of different DNA triplets that can be made using these four bases? (1 mark)

4 possible variations, 3 bases per triplet 4^3 = 64

The sinoatrial node (SAN) is in the right atrium of the heart. Describe the role of the sinoatrial node. (2 marks)

Sends out electrical activity / impulses Initiates the heartbeat / acts as a pacemaker / (stimulates) contraction of atria.

Explain the importance of taking samples at random. (1 mark)

reduces bias

The scientists followed strict safety guidelines when collecting samples of faeces. Apart from the risk of contamination from E. coli this was especially important when collecting samples from humans. Explain why. (1 mark)

(Human) faeces contain pathogens.

At one time, most animal feeds contained antibiotics that increased the rate of animal growth. In the UK, fewer animal feeds now contain antibiotics. Suggest reasons why. (4 marks)

1. (Antibiotic use has) increased cases of bacterial resistance; 2. (Antibiotic) resistant bacteria cause harm / medical treatments less effective; 3. Avoids side effects on animals; 4. Increased demand for organic food. 5. Legislation has controlled antibiotic use, EU/government guidelines

Suggest how the scientists could use DNA to investigate whether the neomycin-resistant bacteria in farmers were identical to the strain of bacteria in the birds they kept. (2 marks)

1. (DNA) hybridisation (of gene for resistance in bacteria taken from bird and farmer); 2. (Identical) strands separate at highest temperature OR 3. Compare base/nucleotide sequence (of gene for resistance in bacteria taken from bird and farmer); 4. (Identical strains) have identical/same base sequences

Suggest and explain one reason for the observed differences in percentage of neomycin-resistant E. coli in turkeys and chickens. (2 marks)

1. (More) antibiotic in turkey feed kills (more) non-resistant bacteria / resistant bacteria survive; 2. (Resistant bacteria) reproduce / pass on gene for resistance;

Three of the bee species collected in the farmland areas were Peponapis pruinosa, Andrena chlorogaster and Andrena piperi. What do these names suggest about the evolutionary relationships between these bee species? Explain your answer. (2 marks)

1. A. chlorogaster and A. piperi are more closely related (to each other than to P. pruinosa); 2. Because they are in the same genus.

Explain why the biologist used a blender and then filtered the mixture (steps 2 and 3). (2 marks)

1. Break open cells / homogenise / produce homogenate; 2. Remove unbroken cells / larger debris;

The carrier molecule on its own may be able to prevent the infection of cells by HIV. Explain how. (2 mark)

1. Carrier binds to (protein on) HIV; 2. Prevents HIV / it binding to (receptor on human) cell.

Suggest and explain two ways in which the scientists could have improved the method used for data collection in this investigation. (2 marks)

1. Collect at more times of the year so more points on graph/better line of best fit on graph. 2. Counted number of individuals in each species so that they could calculate index of diversity. 3. Collected from more sites/more years to increase accuracy of (mean) data.

Use the graph to evaluate the success of the special diet and of the drug in reducing the risk of coronary heart disease. (2 marks)

1. Diet has greater effect in decreasing blood cholesterol concentration; 2. Difficult to judge effect of drug as it is used at same time as diet / drug is not used on its own; 3. Decrease in blood cholesterol concentration linked to reduced risk of heart disease.

The scientists performed statistical tests on the data shown in the graph, to see whether the differences in the amount of mRNA in cells from normal and mutant mice were significant. Both the probability values they obtained were p<0.01. Explain what this means about the differences in the amounts of mRNA produced. (2 marks)

1. Differences significant; 2. Probability of difference being due to chance less than 0.01 / 1%

The scientists' hypothesis was that adding the inhibitor of amylase to the food would lead to a lower blood glucose concentration. Use your knowledge of digestion to suggest how the addition of the inhibitor could lead to a lower blood glucose concentration. (2 marks)

1. Fewer E-S complexes formed; 2. (With inhibitor) less / no starch digested to maltose ; 3. (So) less / no glucose from maltose; 4. (So) less absorption of glucose (from gut).

Apart from the yoghurt, it was important that all of the mice were given the same food each day. Give two reasons why it was important that all of the mice were given the same food each day. (2 marks)

1. Food is a factor affecting blood glucose / different foods contain different amounts of starch / glucose / sugar / carbohydrate; 2. To keep starch / fibre intake the same / similar.

A biologist prepared a sample of organelles labelled C from liver. He used the following method. 1. Added to the liver tissues an ice-cold, buffered solution with the same water potential as the liver tissue. 2. Mixed the liver and solution in a blender. 3. Filtered the mixture from the blender. 4. Spun the filtered liquid in a centrifuge at a low speed. A pellet appeared in the bottom of the centrifuge tube. 5. Poured off the liquid above the pellet into a second centrifuge tube and spun this at a higher speed to obtain the sample of organelles labelled C. Explain why the solution the biologist used was ice-cold, buffered and the same water potential as the liver tissue (step 1). (3 marks)

1. Ice-cold - Slows / stops enzyme activity to prevent digestion of organelles / mitochondria; 2. Buffered - Maintains pH so that enzymes / proteins are not denatured; Reject reference to cells 3. Same water potential - Prevents osmosis so no lysis / shrinkage of organelles / mitochondria / C.

The golf course was surrounded by undeveloped grassland from which it had been produced.The golf course had • some areas of very short grass which was cut frequently • some areas of longer grass which was cut less frequently • some areas of long grass and shrubs which were never cut. The index of diversity for the insects on the golf course was higher than that for the surrounding undeveloped grassland. Explain the effect of developing this golf course on the index of diversity of insects. (3 marks)

1. Increase in variety of plants / shrubs / grass; 2. More habitats / niches; 3. Greater variety of food sources / more food sources.

Use the information provided to identify and explain one way in which the scientists increased the reliability of their method. (2 marks)

1. Large number of farms / farmers (surveyed) 2. So results are (likely to be) representative / can identify anomalous results.

Use information from the graph to suggest how blood glucose concentration is controlled in the mutant mice, compared with the normal mice. (3 marks)

1. Mutant mice (mRNA suggests) make a lot of (the) enzyme; 2. Mutant mice use kidney / intestine (cells) to make glucose; 3. Normal mice do this much less / normal mice use liver cells.

Give one reason why these results may not support the use of the inhibitor of amylase to treat diabetes in mice. (2 marks)

1. Need larger sample / only 30 mice / only 15 mice in each group; 2. Might not be representative / anomalies might have a bigger or smaller effect.

This siRNA would only affect gene expression in cells infected with HIV. Suggest two reasons why. (4 marks)

1. Only infected cells have HIV protein on surface; So carrier only attaches to / specific to these cells / siRNA can only enter these cells 2. siRNA (base sequence) complementary / specific to one mRNA; Only infected cells contain mRNA of HIV / this gene / stops translation of this gene / only binds to this mRNA / destroys this mRNA.

Scientists investigated the control of blood glucose concentration in mice. They kept a group of normal mice without food for 48 hours. After 48 hours, the blood glucose concentrations of the mice were the same as at the start of the experiment. Explain how the normal mice prevented their blood glucose concentration falling when they had not eaten for 48 hours. (3 marks)

1. Release of glucagon; 2. Leads to formation of glucose in liver (cells); 3. From non-carbohydrates / amino acids / fatty acids.

Group A acted as a control in this investigation. Explain the purpose of this group. (2 marks)

1. To show the effect of the inhibitor / drug; 2. To show the effect of yoghurt (on its own does not affect blood glucose).

Suggest two hypotheses the scientists were testing in this investigation. (2 marks)

1. Type of feed affects (antibiotic) resistant bacteria (in animals); 2. Incidence of (antibiotic) resistanct bacteria differs in chickens and turkeys;

From the data in the graphs, a student made the following conclusions. 1. The natural habitat is most favourable for bees. 2. The town is the least favourable for bees. Do the data in the graphs support these conclusions? Explain your answer. (4 marks)

1. Yes, natural appears best because: 1. peak of mean number of bees is highest in natural habitat and remains higher until around day 200 2. mean species richness is consistently higher in this habitat 2. Yes, town is worst because: 1. species richness is lowest from after day 125 2. however, town may not be worst as the mean number of bees in farmland is lower until around 140 3. measure index diversity to decide

Name two structures present in plant cells that are not present in animal cells. (1 mark)

1. chloroplasts 2. cell wall also: •permanent vacuole •starch grains

The scientists collected bees using a method that was ethical and allowed them to identify accurately the species to which each belonged. In each case, suggest one consideration the scientists had taken into account to make sure their method: 1. was ethical. 2. allowed them to identify accurately the species to which each belonged. (2 marks)

1. must not harm the bees/ they must be released unchanged 2. must allow close examination

Mutation 1 leads to the production of a non-functional protein. Explain why. (3 marks)

1. mutation causes a frame shift mutation 2. therefore changes the amino acids being coded for after this point 3. this changes the hydrogen bonds therefore altering the tertiary of the protein making it non-functional

What effect might mutation 2 have on the protein produced? Explain your answer. (2 marks)

1. the mutation occurs in the intron which is non-coding DNA 2. therefore it has no effect on the amino acid sequence as it isn't translated

What is meant by 'species richness'? (1 mark)

A measure of the number of different species in a community.

Below is a diagram of an animal cell. Name the organelles labelled B and C. (2 marks)

B - golgi apparatus C - mitochondria

Explain the overall change in cholesterol concentration in the blood in the first two years. (2 marks)

Diet low in cholesterol / LDLs; Less absorbed into blood / from intestines.

Describe how the concentration of cholesterol in her blood changed over the ten-year period. (2 marks)

Fluctuation and overall decrease; Steep decrease first / after two years and then gradual decrease;

The second centrifuge tube was spun at a higher speed to obtain the sample of organelles labelled C in the diagram (step 5). Suggest why. (1 mark)

Mitochondria / organelle C less dense than nucleus / organelle in first pellet

The student collected data from one part of the golf course and calculated an index of diversity. The table shows her data. Use the formula to calculate the index of diversity for the plants on this part of the golf course. Show your working. (2 marks)

N=36 36(36-1)=1260 216 1260/216 = 5.83

A student investigated the diversity of plants at several sites on a golf course. At each site she took a large number of random samples. Explain the importance of taking a large number of samples at each site. (1 mark)

Produces a more reliable mean / average / makes sure sample was representative / reduce effect of extreme values / identify anomalies.

Name the organelle that made up most of the first pellet after centrifuging at a low speed (step 4). (1 mark)

nucleus

Transcription of a gene produces pre-mRNA. Name the process that removes base sequences from pre-mRNA to form mRNA. (1 mark)

splicing