Author: philcolls76@outlook.com
Last saved by: Gareth Roberts

Carmel College

PAPER 2 practise questions 
Questions I struggled with | What I need to revise to improve

Q1.          The boxes in the diagram represent substances in glycolysis, the link reaction and the Krebs cycle.

(a)     Complete the diagram to show the number of carbon atoms present in one molecule of each compound.
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(b)     Other substances are produced in the Krebs cycle in addition to the carbon compounds shown in the diagram. Name three of these other products.
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(Total 5 marks)

Q2.          The diagram shows a river system in an area of farmland. The numbers show the nitrate concentration in parts per million (ppm) in water samples taken at various locations along the river. Concentrations above 250 ppm encourage eutrophication in the river.

(i)      Explain how farming practices might be responsible for the change in nitrate concentration in the water between point X and point Y.
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(ii)      Describe the effect the nitrate concentration may have in the river at point Y.
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(Total 7 marks)
 
Q3.          Pea plants are leguminous and have nodules on their roots which contain bacteria that are able to fix nitrogen. The diagram shows some of the processes involved in nitrogen fixation by these bacteria.

(a)     Name
(i)      substance X;
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(ii)     substance Y.
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S       (b)     Pea plants respire aerobically, producing ATP which can be used for amino acid synthesis. Describe the role of oxygen in aerobic respiration.
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S       (c)     The bacteria respire anaerobically. This produces hydrogen and ATP used in nitrogen fixation. The hydrogen comes from reduced NAD. Explain how the regeneration of NAD in this way allows ATP production to continue.
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S       (d)     The enzyme nitrogenase is specific to the reaction shown. Explain how one feature of the enzyme would contribute to this specificity.
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S       (e)     Sodium ions act as a non-competitive inhibitor of the enzyme nitrogenase. Explain how the presence of a non-competitive inhibitor can alter the rate of the reaction catalysed by nitrogenase.
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(Total 11 marks)

 

Q4.          The diagram shows the flow of energy through a marine ecosystem.

(a)     Give one reason why not all the light energy falling on the producers is used in photosynthesis.
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(b)     The producers in this ecosystem are seaweeds, which have a large surface area to volume ratio. Give two advantages to seaweeds of having a large surface area to volume ratio.
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S       (c)     Some species of seaweed are submerged in water for most of the time. Explain how being under water might affect the rate of photosynthesis.
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(Total 6 marks)
Q5.          Zooplankton are very small animals which feed on algae (green protoctists) found in lakes. The chart shows the mean depth of zooplankton populations in four lakes, P to S, during the day and the night. It also shows the standard deviations of the means. The depth at which the light intensity is 1% of the surface light intensity is also shown.

S       (a)     Explain the evidence that the zooplankton feed at night.
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(b)     Predatory fish, which hunt by sight, are present in some of the lakes. These fish have been present in the lakes for different lengths of time.
 
Lake | Estimated length of time predatory fish have been present / years
P | 0
Q | 5
R | 25
S | Over 1000

(i)      Describe the relationship between the depth of the zooplankton during the day and the length of time predators have been present in the lake.
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S       (ii)     Suggest how the differences in behaviour of the zooplankton populations in the four lakes might have evolved.
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(Total 7 marks)

Q6.          (a)     Name the two substances produced by anaerobic respiration in humans.
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(b)     When an athlete runs in a 100 metre race, 90% of the energy needed is provided by anaerobic respiration.
(i)      Explain why most of the energy is provided by anaerobic respiration rather than aerobic respiration.
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(ii)     The athlete continues to breathe deeply for several minutes after the race ends. Explain why this is necessary.
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(Total 6 marks)
Q7.          The graph shows dissociation curves for human oxyhaemoglobin at rest and during exercise.
Table 1 gives information about conditions in the body at rest and during exercise.

 
| Rest | Exercise
Plasma pH | 7.4 | 7.2
Blood temperature / °C | 37.0 | 39.0
Alveolar partial pressure of oxygen / kPa | 13.3 | 13.3
Tissue partial pressure of oxygen / kPa | 5.0 | 4.0

Table 1
(a)     What is meant by the term partial pressure?
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(b)     Use Table 1 and the graph to calculate the difference in the percentage saturation of haemoglobin in the tissues between rest and exercise.

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(c)     Explain the differences between the figures shown in Table 1 for rest and exercise.
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(d)     Explain the advantage of the difference in position of the dissociation curve during exercise.
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Table 2 shows how the oxygen concentration in the blood going to and from a muscle changes from rest to heavy exercise.

Oxygen concentration / cm^3 per 100 cm^3
blood

| Blood in arteries | Blood in veins
At rest | In solution | 0.3 | 0.2
| As oxyhaemoglobin | 19.5 | 15.0
| Total oxygen | 19.8 | 15.2
During heavy exercise | In solution | 0.3 | 0.1
| As oxyhaemoglobin | 20.9 | 5.3
| Total oxygen | 21.2 | 5.4

Table 2
(e)     By how many times is the volume of oxygen removed from the blood by the muscle in Table 2 during heavy exercise greater than the volume removed at rest?
Show your working.

 
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(f)      Does enriching inspired air with oxygen have any effect on the amount of oxygen reaching the tissues? Support your answer with evidence from the graph and Table 2.
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S       (g)     The change to the dissociation curve is one of a number of ways in which the total oxygen supplied to muscles is increased during exercise. Give two other ways in which the total oxygen supplied to muscles during exercise is increased.
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(Total 15 marks)
Q8.          Mayflies are insects which lay their eggs in streams and rivers. The nymphs which hatch from the eggs live in the water for several years.
Mayfly nymphs were collected by disturbing the gravel of a stream bed. A net placed immediately downstream caught any animals which were washed out of the gravel. Eight samples were collected from shallow, fast-flowing parts of the stream and eight from deeper, slow-flowing parts. Nymphs from two different families of mayfly were found. The results are given in the table.
 
| | Family Caenidae | Family Baetidae
| | Shallow water | Deep water | Shallow water | Deep water
| Mean number of nymphs | 2.38 | 12.88 | 24.50 | 6.00
| Standard deviation | 1.51 | 7.92 | 6.72 | 1.51

(a)     Describe how you would have collected the samples in order to ensure they were representative of the habitats being investigated and could be compared with each other.
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(b)     Which one of the four samples showed the greatest variation within the sample? Give evidence from the table for your answer.
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(c)     The two families of mayfly nymph occupy different ecological niches.
(i)      What is meant by the term ecological niche?
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(ii)     Describe the evidence in the table which suggests that the two families of mayflies occupy different ecological niches.
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(iii)     Explain the advantage to these two families of mayflies of occupying different ecological niches.
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(Total 8 marks)
Q9.          There is evidence that the first photosynthetic organisms were primitive water-dwelling bacteria. The very first of these lived near the surface of the water in lakes and contained a purple pigment that absorbed light most strongly in the green region of the spectrum. Later, other bacteria evolved that lived on the top of sediment at the bottom of the lakes (Figure 1). Gene mutations had enabled these bacteria to synthesise chlorophyll instead of the purple pigment present in the bacteria living near to the surface. Chlorophyll absorbs light most strongly in the blue and red regions of the spectrum (Figure 2).
Figure 1

Figure 2

(a)     Describe how light energy absorbed by chlorophyll molecules is used to synthesise ATP.
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(b)     Use Figure 2 to explain how natural selection would favour the evolution of sediment-dwelling bacteria containing a different photosynthetic pigment from those living near the surface of the water.
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(Total 11 marks)
Q10.          Ions of metals such as zinc often pollute rivers. The effect of zinc ions on gas exchange and respiration in fish was investigated. Fish were kept in tanks of water in a laboratory.
The fish in one group (X) had a solution of a zinc compound injected directly into their blood and were then put in a tank of zinc-free water. A second group (Y) was not injected but had the solution of the zinc compound added to the water in the tank.

The partial pressure of oxygen in the blood of both groups of fish was then monitored. The results are shown in the graph.

(a)     During this investigation, the water temperature in the tanks was kept constant. Explain why changes in the water temperature might lead to the results of the investigation being unreliable.
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(b)     The results from the two groups were compared using a statistical test.
(i)      Suggest a null hypothesis that could be tested.
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(ii)     Explain why it is important to use a statistical test in analysing the results of this investigation.
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(c)     Two suggestions were made to explain the results shown in the graph.
A       Zinc ions reduce the rate at which oxygen is taken up from the water and passes into the blood.
B       Zinc ions reduce the ability of haemoglobin to transport oxygen.
Which of these suggestions is the more likely? Explain the evidence from the graph that supports your answer.
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(d)     During the investigation, the pH of the blood was also monitored. It decreased in group Y. Suggest an explanation for this decrease in pH.
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(e)     Leaves were collected from sycamore trees growing in a polluted wood and the concentration of some metal ions in samples of these leaves was measured. Woodlice were then fed with the leaves. After 20 weeks, the concentration of the ions in the bodies of the woodlice was measured. Some of the results are shown in the table.
 
| Concentration of ions / µg g^–1
| Copper | Cadmium | Zinc | Lead
Leaves | 52 | 26 | 1430 | 908
Woodlice | 1130 | 525 | 1370 | 132

(i)      Which of the elements shown in the table is concentrated most by the woodlice? Use suitable calculations to support your answer.

 
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(ii)     Suggest what happens to most of the lead ions in the leaves eaten by the woodlice.
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(iii)     Explain the difference in the copper ion concentration between the leaves and the woodlice.
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(f)      Yorkshire fog is a species of grass. Two varieties of Yorkshire fog were studied. One variety was tolerant to arsenic, while the other variety was not. In a series of investigations, it was found that
•        Arsenic-tolerant plants grow in soil which contains a high concentration of arsenic.
•        Arsenic-tolerant plants growing in soil containing high concentrations of arsenic and phosphorus-containing compounds have very low concentrations of arsenic in their cells. They also have low concentrations of phosphates in their cells. Arsenic and phosphorus are chemically similar.
•        Plants that are not tolerant to arsenic grow poorly on soil which has a high concentration of both arsenic and phosphorus-containing compounds.
•        Tolerance to arsenic in Yorkshire fog is caused by a single gene with the allele, a, for tolerance recessive to the allele, A, for non-tolerance.
(i)      What caused the allele for tolerance to first arise?
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(ii)     Give two functions of phosphates in plant cells.
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(iii)     Arsenic-tolerant Yorkshire fog plants are very rare in areas with low concentrations of arsenic in the soil, even where the soil has a high concentration of phosphate. Explain why they are unable to compete in these conditions with plants that are not tolerant to arsenic.
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(3)(Total 20 marks)
Q11.During the last 50 years, there have been changes in the climate of the UK. One of the main changes is temperature. The data in the following resources all relate to southern England.
Figure 1 shows the mean temperatures for January and February combined.
Figure 1
 
Figure 2 shows the mean temperatures for March.
Figure 2
 
Birds, such as chaffinches, have been recorded as breeding earlier. Chaffinches build nests. When the nest is complete, the female lays eggs until she has produced a full clutch of 4 to 6 eggs. After the eggs hatch, the parent birds feed the young on insects.
Figure 3 shows the mean date on which chaffinches laid their first egg.
Figure 3

The data from which this graph was drawn were collected by volunteers. They used standard record cards. The volunteers used one record card for each nest they found. Each card was used to record
•        the geographical location
•        the habitat in which the nest site was situated
•        the date of each visit to the nest by the volunteer
•        the number of eggs present in the nest at each visit.
Visits were made to the nests at least once every 5 days.
(a)     Do the data in Figure 1 and Figure 2 support the idea that there has been a rise in the mean temperatures in southern England between 1970 and 2000? Explain your answer.
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(b)     Describe briefly how you would use a statistical test to find whether there is a significant correlation between mean March temperature and the date when chaffinches laid their first egg.
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(c)     In chaffinches, the date of laying the first egg is determined by a number of factors. These include day length and temperature. What is the advantage to the bird of egglaying being determined by
(i)      daylength
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(ii)     temperature?
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(d)     Scientists found that there was a correlation between mean annual temperature and the date when chaffinches laid the first egg. Can you conclude that higher temperatures cause earlier laying of the first egg?
Explain your answer.
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(e)     How does the way in which the data were collected affect the conclusions which can be drawn from Figure 3?
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Q12.          (a)     The concentrations of carbon dioxide in the air at different heights above ground in a forest changes over a period of 24 hours. Use your knowledge of photosynthesis to describe these changes and explain why they occur.
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(b)     In the light-independent reaction of photosynthesis, the carbon in carbon dioxide becomes carbon in triose phosphate. Describe how.
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(Total 10 marks)
Q13.          Much of Indonesia is covered with forest. Large areas of forest have been cleared and planted with oil-palm trees to be used in the production of fuel.
(a)     In these forests, nitrogen in dead leaves is made available to growing plants by the action of bacteria. Describe the role of bacteria in making the nitrogen in dead leaves available to growing plants.
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(b)     During photosynthesis, oil-palm trees convert carbon dioxide into organic substances. Describe how.
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(Total 11 marks)
Q14.          Scientists measured the mean temperature in a field each month between March and October. The table shows their results.
 
| Month | Mean temperature /°C
| March | 9
| April | 11
| May | 14
| June | 17
| July | 20
| August | 18
| September | 16
| October | 14

(a)     The gross productivity of the plants in the field was highest in July.
Use the data in the table to explain why.
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(b)     (i)      Give the equation that links gross productivity and net productivity.
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(ii)     The net productivity of the plants in the field was higher in August than in July. Use the equation in part (b)(i) and your knowledge of photosynthesis and respiration to suggest why.
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(c)     A horse was kept in the field from March to October. During the summer months, the horse was able to eat more than it needed to meet its minimum daily requirements.
Suggest how the horse used the extra nutrients absorbed.
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(d)     The horse’s mean energy expenditure was higher in March than it was in August. Use information in the table to suggest why.
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(Total 8 marks)
Q15.(a)     The table contains statements about three biological processes.
Complete the table with a tick if the statement in the first column is true, for each process.
 
| | Photosynthesis | Anaerobic respiration | Aerobic respiration
| ATP produced | | |
| Occurs in organelles | | |
| Electron transport chain involved | | |

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(b)     Write a simple equation to show how ATP is synthesised from ADP.
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(c)     Give two ways in which the properties of ATP make it a suitable source of energy in biological processes.
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(d)     Humans synthesise more than their body mass of ATP each day. Explain why it is necessary for them to synthesise such a large amount of ATP.
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(Total 8 marks)

Q16.(a)     ATP is useful in many biological processes. Explain why.
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(b)     Describe how ATP is made in mitochondria.
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(c)     Plants produce ATP in their chloroplasts during photosynthesis. They also produce ATP during respiration. Explain why it is important for plants to produce ATP during respiration in addition to during photosynthesis.
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Q17.A scientist investigated the use of a new source of carbohydrate in the production of ethanol for biofuel. He wanted to find the optimum time to leave a mixture of yeast and this carbohydrate to produce ethanol. The scientist set up an airtight container containing yeast and this carbohydrate. He then measured the oxygen, carbon dioxide and ethanol concentrations over 8 hours.
The results of his investigation are shown in the graph below.

 
(a)     The scientist used a container that was airtight.
Give two explanations why the container had to be airtight.
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(b)     Explain the relationship between the concentration of oxygen and the concentration of carbon dioxide between 0 and 3 hours.
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(c)     The scientist concluded that yeast starts to respire anaerobically when the oxygen concentration falls below a certain concentration. What is the oxygen concentration when the yeast starts to respire anaerobically? Explain your answer.
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(d)     (i)      The scientist worked for a biofuel company. Give two suggestions for further work he should do to make sure that the results he presented to the company were reliable.
Explain how each of your suggestions would make the results more reliable.
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(ii)     The scientist recommended that when the ethanol is produced commercially as biofuel the reaction should be stopped at 6 hours. Use the graph to suggest why.
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(iii)    The scientist’s work was funded by a biofuel company. Explain why the source of funding can cause problems with scientific work.
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(Total 16 marks)
Q18.Figure 1 shows the effect of wavelength on the percentage of light absorbed by the chlorophyll from these seaweeds.
Figure 1

Some scientists investigated the growth of these seaweeds in artificial conditions.
They investigated the effect of different lamps on the rate of photosynthesis of the seaweeds.
•        Lamp P produced light containing all wavelengths of visible light. (450 to 750 nm)
•        Lamp Q only produced light of wavelength 460 nm.

The scientists measured photosynthesis by recording the rate of oxygen production. Their results are shown in Figure 2.
Figure 2
 
| | Mean rate of photosynthesis / arbitrary units ( ± standard deviation)
| Species | Lamp P Light of all wavelengths of visible light | Lamp Q Light of wavelength 460nm
| Ulva pertusa | 1300.9 ( ± 125.4) | 776.6 ( ± 105.6)
| Mastocarpus yendoi | 318.9 ( ± 69.5) | 299.6 ( ± 83.2)

(a)     Between 500 and 700 nm, what range of wavelengths of light is absorbed least by chlorophyll?
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(b)     The scientists measured the oxygen produced by the light-dependent reaction of photosynthesis. Name two other substances produced by the light-dependent reaction.
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(c)     (i)      The scientists measured the rate of photosynthesis of the seaweeds in this investigation in terms of oxygen produced.
Suggest the units they should use.
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(ii)     This investigation was carried out in bright light. Explain why reducing the light intensity would affect the amount of oxygen released by the seaweeds.
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(d)     In this investigation, the scientists kept the temperature at 15 °C. A student suggested that repeating the investigation at 20 °C would not affect the amount of oxygen released by the seaweed. Evaluate this suggestion.
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(e)     (i)      Did the type of lamp used affect the rate of photosynthesis in M. yendoi? Explain the evidence for your answer.
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(2)

(ii)     The different lamps resulted in different rates of photosynthesis by U. pertusa. Explain why there was a higher rate of photosynthesis when the seaweed was illuminated with lamp P.
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(Extra space) ........................................................................................
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(3)
(Total 16 marks)
Q19.(a)     Energy enters most ecosystems through the light-dependent reaction of photosynthesis. Describe what happens during the light-dependent reaction.
(5)

(b)     Changes in ecosystems can lead to speciation. A high concentration of copper in soil is toxic to most plants. In some areas where the soil is polluted with copper, populations of grasses are found to be growing. These populations of grass belong to a species also found growing on unpolluted soils.
It has been suggested that a new species of grass may evolve on soil that has been polluted with copper. Explain how this new species might evolve.

(5)
(Total 10 marks)
Q20.(a)     On islands in the Caribbean, there are almost 150 species of lizards belonging to the genus Anolis. Scientists believe that these species evolved from two species found on mainland USA. Explain how the Caribbean species could have evolved.

(6)
(b)     Anolis sagrei is a species of lizard that is found on some of the smallest Caribbean islands. Describe how you could use the mark-release-recapture method to estimate the number of Anolis sagrei on one of these islands.

(4)

(c)     Large areas of tropical forest are still found on some Caribbean islands. The concentration of carbon dioxide in the air of these forests changes over a period of 24 hours and at different heights above ground.
Use your knowledge of photosynthesis and respiration to describe and explain how the concentration of carbon dioxide in the air changes:
•        over a period of 24 hours
•        at different heights above ground.

(5)
(Total 15 marks)
Q21.Multiple sclerosis (MS) is a condition caused when the body’s own immune system attacks the myelin sheath around axons. The cell bodies of the neurones themselves can also be damaged or destroyed. People with MS usually have periods of time when their MS gets no worse, followed by relapses when it gets worse.
Scientists investigated the effects on neurones of damage to myelin. The scientists obtained a modified antigen from the myelin sheath of humans and injected it into mice. After a number of days, this injection of antigen resulted in the myelin sheaths in the mice being damaged. Some cell bodies of neurones were also damaged.
(a)     Suggest how the injection of the antigen resulted in the myelin sheaths being damaged.
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(3)
(b)     The scientists compared the ultrastructure of normal and damaged neurones. They found that damaged neurones contained many mitochondria with an unusual ultrastructure.
The diagram shows a mitochondrion with normal ultrastructure and one with the unusual ultrastructure.
 
Suggest why having a large number of mitochondria with this unusual ultrastructure could lead to neurones dying.
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 (3)
(c)     The scientists took a large number of photographs of thin sections through neurones.
Using these photographs, they found that 40% of mitochondria had the unusual ultrastructure in damaged neurones.
(i)      What sort of microscope would the scientists use to take the photographs?
Give one reason for your answer.
Type of microscope....................................................................................
Reason ......................................................................................................
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(1)
(ii)     Suggest how the scientists found the percentage of mitochondria with the unusual ultrastructure.
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(3)
(Total 10 marks)
Q22.          Figure 1 shows part of a sarcomere.

Figure 1
(a)     (i)      Name the main protein in structure B.
.............................................................................................................(1)
(ii)     Name the structure in box A.
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(1)
(b)     (i)      Describe how calcium ions cause the myofibril to start contracting.
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(2)
(ii)     Describe the events that occur within a myofibril which enable it to contract.
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(3)
Slow and fast skeletal muscle fibres differ in a number of ways. Slow fibres get their ATP from aerobic respiration while anaerobic respiration provides fast fibres with their ATP. Figure 2 shows a bundle of fast and slow fibres seen through an optical microscope. The fibres have been stained with a stain that binds to the enzymes which operate in the electron transport chain.

Figure 2
S       (c)     (i)      Describe how you could calculate the percentage of fast fibres in this bundle.
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(1)

(ii)     The figure calculated by the method in part (c)(i) may not be true for the muscle as a whole. Explain why.
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(1)

(d)     The fibres in Figure 3 correspond to those in region X of Figure 2. They were stained with a substance that binds to enzymes involved in glycolysis. Shade Figure 3 to show the appearance of the fibres. Use the shading shown in the key.

Figure 3
(2)

S       (e)     Recent research has shown that the difference in fibre types is due in part to the presence of different forms of the protein myosin with different molecular shapes.
Explain how a new form of myosin with different properties could have been produced as a result of mutation.
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(4)
(Total 15 marks)

Q23.Anti-diuretic hormone (ADH) is released into the blood in response to a shortage of water in the body. ADH enters the collecting duct cells in nephrons and causes the increased synthesis of one type of protein molecule. These protein molecules are inserted into the plasma membranes of the collecting duct cells where they act as channels. Only water molecules can pass through these channels, increasing the reabsorption of water from the kidney filtrate.
(a)     Name the gland which releases ADH.
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(1)

(b)     (i)      Explain how the structure of protein molecules allows them to form channels through which only water molecules can pass.
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(2)

(ii)     Explain how the cells of the collecting duct are able to absorb water from the filtrate through the protein channels in their plasma membranes.
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(2)
(Total 5 marks)

Q24.          Secretion of neurotransmitters into a synaptic cleft may produce an action potential in a postsynaptic neurone.
(i)      Explain how the release of acetylcholine at an excitatory synapse reduces the membrane potential of the postsynaptic membrane.
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(2)

(ii)      Explain what causes transmission at a synapse to occur in only one direction.
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(2)

(iii)     GABA is a neurotransmitter which inhibits the production of action potentials.
The diagram and the graph show how the release of GABA from a presynaptic membrane affects the membrane potential of a postsynaptic membrane.

When the postsynaptic membrane is stimulated by acetylcholine, an action potential is less likely if GABA is released at the same time. Explain why.
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Q25.          The flow chart outlines an investigation to determine from where the calcium ions involved in muscle contraction are released.
Calcium ion transport proteins were
isolated from human tissue.
↓
These proteins were injected into a rabbit.
↓
The rabbit formed antibodies to the
proteins. These antibodies were collected
and labelled with gold particles.
↓
Muscle tissue was treated with the
labelled antibodies and examined with an
electron microscope. High concentrations
of gold particles were observed attached
to the sarcoplasmic reticulum.
S       (a)     Labelled antibodies and an electron microscope can be used to produce images locating proteins on the surface of organelles, but cannot be used to observe cross bridge cycling in muscle cells. Explain why.
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 (5)
(b)     Describe the role of calcium ions and ATP in muscle contraction.
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(5)
(Total 10 marks)
Q26.(a)     The control of water balance in the body involves negative feedback.
(i)      Describe what is meant by negative feedback.
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(1)

(ii)     Water is removed from the body via the kidneys. Give two other ways in which water is removed from the body.
1 ............................................................................................................
2 ............................................................................................................
(2)

(iii)    Name the part of the brain which acts as the coordinator in the control of water balance.
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(1)

(b)     Figure 1 shows the cells lining the collecting duct in a human kidney. ADH molecules bind to the receptor proteins and this triggers the vesicles containing aquaporins to bind with the plasma membrane next to the lumen. Figure 2 shows an aquaporin which is a large channel protein.
Figure 1

Figure 2

(i)      From which gland is ADH released?
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(1)

(ii)     Use the information given to explain how ADH increases the movement of water from the lumen of the collecting duct into the blood.
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(4)

(c)     The gene for the ADH receptor proteins is found on the X chromosome. One allele of this gene causes a non-functioning receptor protein to be made. This allele is recessive and is one cause of the condition called diabetes insipidus.
(i)      What would be the most obvious symptom of diabetes insipidus?
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(1)
(ii)     Suggest why diabetes insipidus is more common in males.
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(2)
(iii)    A recessive allele which has harmful effects is able to reach a higher frequency in a population than a harmful dominant allele. Explain how.
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(3)
(Total 15 marks)
Q27.          (a)     Sucrose, maltose and lactose are disaccharides.
(i)      Sucrase is an enzyme. It hydrolyses sucrose during digestion. Name the products of this reaction.
................................................... and ..................................................
(2)

(ii)     Sucrase does not hydrolyse lactose. Use your knowledge of the way in which enzymes work to explain why.
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(2)
(b)     A woman was given a solution of sucrose to drink. Her blood glucose concentration was measured over the next 90 minutes. The results are shown on the graph.

(i)      Describe how the woman’s blood glucose concentration changed in the period shown in the graph.
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(2)
(ii)     Explain the results shown on the graph.
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(2)

(Total 8 marks)
Q28.(a)    Describe the part played by each of the following in myofibril contraction.
(i)      Tropomyosin
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(2)

(ii)     Myosin
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(2)
(b)     The table shows features of fast and slow muscle fibres.
 
| Feature | Fast muscle fibre | Slow muscle fibre
| Type of respiration | Mainly anaerobic | Mainly aerobic
| Glycogen | High concentration | Low concentration
| Capillaries | Few | Many

Use information from the table to suggest and explain one advantage of:
(i)      the high glycogen content of fast muscle fibres
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(2)

(ii)     the number of capillaries supplying slow muscle fibres.
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(2)
(Total 8 marks)
Q29.Multiple sclerosis (MS) is a disease that involves damage to the myelin sheaths of neurones. Movement in MS sufferers may be jerky or slow.
(a)     Damage to the myelin sheaths of neurones can lead to problems controlling the contraction of muscles.
Suggest one reason why.
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[Extra space] ................................................................................................
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(2)

Scientists investigated the use of substances called cannabinoids to control muscle problems caused by MS.
(b)     Cannabinoids are hydrophobic molecules. In the body, they easily pass into neurones.
Explain why.
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........................................................................................................................(1)
(c)     Cannabinoid receptors are found in the pre-synaptic membrane of neuromuscular junctions. When a cannabinoid binds to its receptor, it closes calcium ion channels.
Suggest how cannabinoids could prevent muscle contraction.
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[Extra space] ................................................................................................
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(d)     Cannabinoids include substances found in cannabis that can enter brain tissue. Scientists are developing artificial cannabinoids that can enter neuromuscular junctions but cannot enter brain tissue.
Suggest why these artificial cannabinoids would be better to use than cannabis when treating someone with MS.
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[Extra space] ................................................................................. (2)(Total 9 marks)
Q30.Malaria is a disease that is spread by insects called mosquitoes. In Africa, DDT is a pesticide used to kill mosquitoes, to try to control the spread of malaria.
Mosquitoes have a gene called KDR. Today, some mosquitoes have an allele of this gene, KDR minus, that gives them resistance to DDT. The other allele, KDR plus, does not give resistance.
Scientists investigated the frequency of the KDR minus allele in a population of mosquitoes in an African country over a period of 10 years.
The figure below shows the scientists’ results.
  
          Year
(a)     Use the Hardy–Weinberg equation to calculate the frequency of mosquitoes heterozygous for the KDR gene in this population in 2003.
Show your working.

 
 
Frequency of heterozygotes in population in 2003 ...................................(2)
(b)     Suggest an explanation for the results in the figure above.
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The KDR plus allele codes for the sodium ion channels found in neurones.
(c)     When DDT binds to a sodium ion channel, the channel remains open all the time.
Use this information to suggest how DDT kills insects.
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........................................................................................................................(2)
(d)     Suggest how the KDR minus allele gives resistance to DDT.
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........................................................................................................................(2)
(Total 10 marks)
Q31.Interferon gamma is a substance secreted by some types of white blood cells, including helper T cells. It regulates the production of a number of proteins by target cells. Which protein is produced depends on the type of target cell.
The diagram shows how interferon gamma regulates three genes.

(a)     Use information in the diagram to suggest how the binding of interferon gamma to its receptor protein leads to the production of phosphorylated STAT1.
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(2)

(b)     Name the two transcription factors in the diagram.
1 ..........................................................................................................................
2 ..........................................................................................................................
(2)
(c)     The regulation of the formation of helper T cells by interferon gamma is an example of positive feedback.
Explain why it is an example of positive feedback.
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(d)     The IRF gene can be a tumour suppressor gene.
Use the information in the diagram to explain how the IRF gene acts as a tumour suppressor gene.
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.............................................................................................................................(3)
(Total 9 marks)
Q32.Answers should be written in continuous prose, where appropriate.
Quality of Written Communication will be assessed in these answers.
The kidney plays an important part in the regulation of blood water potential. This involves control of the amount of water reabsorbed from the filtrate produced in the kidney tubules. The amount of water reabsorbed affects the volume of urine produced, the rate at which the bladder fills and how often it has to be emptied.
(a)     Explain how the loop of Henle maintains the gradient of ions which allows water to be reabsorbed from filtrate in the collecting duct.
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 (5)

(b)     Explain how ADH is involved in the control of the volume of urine produced.
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(4)

(c)     The diagram shows the systems involved in controlling the emptying of the bladder. In babies, emptying of the bladder is controlled by an autonomic reflex involving the internal sphincter muscle. Conscious control is learnt between the ages of two and three and involves the external sphincter as well.

Using information in the diagram,
explain how the autonomic reflex arc is different from a simple reflex arc involving voluntary muscle;
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(2)
(Total 11 marks)

Q33.          (a)     A woman takes moderate exercise. Explain what causes her heart rate to increase while she exercises.
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(6)
(b)     An electrocardiogram (ECG) measures the electrical changes occurring in cardiac muscle as a heart is beating. An ECG trace for a healthy person and an ECG trace for a person suffering from heart disease are shown.

(i)      Describe the route taken when electrical impulses are transmitted from the sinoatrial node to the muscles of the ventricles in a healthy heart.
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(2)

(ii)     Explain how information from these ECG traces suggests that the damage caused to the diseased heart is unlikely to have affected the sinoatrial node.
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(2)
(Total 10 marks)
Q34.          (a)     A woman takes moderate exercise. Explain what causes her heart rate to increase while she exercises.
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(6)

(b)     An electrocardiogram (ECG) measures the electrical changes occurring in cardiac muscle as a heart is beating. An ECG trace for a healthy person and an ECG trace for a person suffering from heart disease are shown.

(i)      Describe the route taken when electrical impulses are transmitted from the sinoatrial node to the muscles of the ventricles in a healthy heart.
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(2)

(ii)     Explain how information from these ECG traces suggests that the damage caused to the diseased heart is unlikely to have affected the sinoatrial node.
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(2)
(Total 10 marks)

Q35.          (a)     Explain how a rise in blood pressure results in a decrease in the rate of heartbeat.
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(6)

(b)     Some drugs inhibit the transmission of nerve impulses to the heart. Explain how these drugs reduce high blood pressure.
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(2)
(Total 8 marks)
 
TOPICS 3.7 and 3.8 + comprehension question practice

Q1.A species of flowering plant can have white, red or purple flowers. The colour of the flowers is controlled by two genes. Each gene is found on a different chromosome, and is responsible for one step in a biosynthetic pathway. The biosynthetic pathway is

Gene 1 has the dominant allele A and the recessive allele a. Gene 2 has the dominant allele B and the recessive allele b. In both cases, the dominant allele needs to be present for the production of the associated enzyme.
(a)     Explain how the two genes are involved in producing white, red or purple flowers.
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(6)

(b)     (i)      A homozygous red-flowered plant was crossed with a homozygous white-flowered plant. All the flowers of the offspring were purple. What was the genotype of
the red-flowered parent;
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the white-flowered parent?
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(2)

(ii)     The purple-flowered offspring were crossed. What phenotypic ratio would you expect in the next generation? Use a genetic diagram to explain your answer.

 
 
(4)

(c)     (i)      Genetically, there are different types of white-flowered plants of this species. Give their different genotypes.
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(1)

(ii)     You have samples of fresh petals from the two homozygous types of white flowers, and a pure sample of the red pigment, K. Explain, in outline, how you might distinguish the two types of petal from each other.
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(2)
(Total 15 marks)

Q2.The diagram shows the inheritance of coat colour in pigs through three generations.

(a)     Explain one piece of evidence from the diagram which shows that coat colour is not controlled by one gene with two codominant alleles.
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(3)

Two hypotheses were put forward to explain the results, each based on the action of two pairs of alleles.
 
| | Hypothesis 1 | Hypothesis 2
| Phenotype | Genotype | Genotype
| Red | A_B_ | A_B_ or A_bb
| Sandy | A_bb or aaB | aaB_
| White | aabb | aabb

( _ represents either a dominant or a recessive allele of the gene)
(b)     Assuming that Hypothesis 1 is correct, give one possible genotype for each of the following individuals in the diagram.
11 .....................................................
10 .....................................................
2 .......................................................
(2)

(c)     Explain one piece of evidence from the diagram which shows that Hypothesis 2 should be rejected.
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(2)

(d)     Individual 18 was crossed with a pig of genotype Aabb.
Use Hypothesis 1 to predict the genotypes and the ratio of phenotypes expected in the
offspring of this cross.
 
| | Individual 18 | Other parent
| Parental genotypes | ................................. | Aabb

Parental
gametes

Offspring
genotypes

Offspring
phenotypes

Expected ratio
of offspring
phenotypes

(4)
(Total 11 marks)

Q3.          The vegetation on a large heap of waste from an old mine was investigated. The table shows the results of the measurements of certain factors in 1m^2 frame quadrats placed on the south-facing slope.

Quadrat

Angle of
slope / °

Vegetation
cover / %

Moisture
content of
soil / %

pH of
soil

1
2
3
4
5
6

45
30
25
12
7
1

60
70
68
100
85
100

17.2
14.6
20.3
23.5
21.0
21.2

5.6
4.2
5.2
7.1
5.4
6.8

(a)     Which of the factors measured are abiotic?
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(1)

(b)     Describe how the investigators could obtain the value for vegetation cover in each quadrat.
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(2)

(c)     The correlation between vegetation cover and soil moisture content was tested statistically. These two factors were found to be positively correlated, and p < 0.05. Explain what this result means.
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(2)

S       (d)     At first the waste heap had no plants growing on it. Some of the first plants to colonise it were small herbaceous plants. Explain one way in which colonisation by herbaceous plants could change the physical environment.
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(2)
(Total 7 marks)

Q4.          A sex-linked gene controls fur colour in cats. Ginger-coloured fur is controlled by the allele G, and black-coloured fur is controlled by the allele g. Some female cats have ginger and black patches of fur. They are described as tortoiseshell. Male cats cannot be tortoiseshell.
(a)     What is meant by a sex-linked gene?
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(1)

(b)     A male cat with the genotype X^g Y mates with a tortoiseshell female.
(i)      Give the phenotype of the male.
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(1)

(ii)     Give the genotype of the tortoiseshell female.
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(1)

(iii)     Complete the genetic diagram to show the genotypes and the ratio of phenotypes expected in the offspring of this cross.
Parents                                     Male                     Tortoiseshell female
Parental genotypes                  X^g Y                        ........................
 
Parental gametes

Offspring genotypes

Offspring phenotypes
 
Ratio							(3)
(c)     The effect of the G and g alleles is modified by another gene. This gene is not sex-linked and it has two alleles. The allele d changes the ginger colour to cream and the black colour to grey. The dominant allele D does not modify the effect of G or g.
A cream-coloured male cat mated with a black female whose genotype was X^gX^g Dd. Male kittens of two different colours were produced. Complete the genetic diagram.
          Parental                                  Cream-coloured                     Black
phenotypes                                     male                              female
 
          Parental                                    .....................                        X^gX^g Dd
genotypes
 
          Parental
gametes
 
          Male kitten
genotypes
 
          Male kitten
colours							(3)   (Total 9 marks)
Q5.          Figure 1 and Figure 2 show the chromosomes from a single cell at different stages of meiosis.

Figure 1                                                                    Figure 2
(a)     What is the diploid number of chromosomes in the organism from which this cell was taken?
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(1)

(b)     Describe what is happening to the chromosomes at the stage shown in
(i)      Figure 1;
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(2)

(ii)     Figure 2.
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(2)

(c)     (i)      The genotype of this organism is Bb. The locus of this pair of alleles is shown in Figure 1.
Label two chromosomes on Figure 2 to show the location of the B allele and the location of the b allele.
(1)

(ii)     How many genetically different gametes can be produced by meiosis from a cell with the genotype, Bb Cc Dd? Assume these genes are located on different pairs of homologous chromosomes. Show your working.

 
 
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(2)
(Total 8 marks)
Q6.          (a)     The diagram shows a number of stages in an ecological succession in a lake.

Explain how the diagrams illustrate the features of an ecological succession.
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(b)     Several small rivers flow into this lake. These rivers flow through forested areas.
Explain how deforestation might affect the process of succession in the lake.
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S       (c)     Stage 5 illustrates the final stage of succession which is known as the climax community. During this stage the number of different species in the habitat and the size of each population remain fairly constant. Explain what limits the size of populations in a climax community.
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(Total 13 marks)
Q7.          Climatic factors, such as temperature and rainfall, vary greatly over short distances across mountain ranges. In an investigation, populations of the plant, Achillea lanulosa, were sampled from several sites on a transect across a mountain range. At each sampling site, seeds were collected at random. Each batch of seeds was germinated and grown to maturity under the same experimental conditions.
The diagram shows
•        a profile indicating the position and altitude of the sampling sites
•        the mean height of mature plants grown from each sample of seeds
•        the standard deviation of heights of the mature plants grown from each sample of seeds.

(a)     (i)      Give one limitation of using a line transect to collect these data.
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(1)

(ii)     Suggest how plants should be chosen at each sampling site to avoid bias and to be representative.
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(b)     (i)      What information does the bar representing standard deviation give about the plants in a sample?
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(ii)     Describe what the results show about the variation of the height of the plants in relation to altitude.
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S       (iii)     There was a significant difference between the mean heights of the plants grown from seeds taken from sites A and D. Describe the evidence from the information given which shows that this is likely to be due to genetic differences between the two populations.
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(1)
(Total 7 marks)

Q8.          The production of pigment in rabbit fur is controlled by two genes.
One gene controls whether any pigment is made. This gene has three alleles. Allele A codes for the production of one form of the enzyme tyrosinase, which converts tyrosine into a black pigment. Allele A^h codes for the production of a second form of the enzyme, which becomes inactive at temperatures close to a rabbit’s core body temperature, so only the face, ears, legs and tail are pigmented. A third allele, a, fails to code for a functional tyrosinase.
The other gene controls the density of pigment in the fur. This gene has two alleles. Allele B is dominant and results in the production of large amounts of pigment, making the fur black.
Allele b results in less pigment, so the fur appears brown.
(a)     How do multiple alleles of a gene arise?
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(2)
(b)     The table shows some genotypes and phenotypes.
 
Genotype | Phenotype
A–B– | all fur black
aaB– | all fur white (albino)
A^habb | white body fur with brown face, ears, legs and tail (Himalayan)

(i)      What do the dashes represent in the genotype of the black rabbit?
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(1)

(ii)     Give all the possible genotypes for a Himalayan rabbit with black face, ears, legs and tail.
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(2)

(iii)     Suggest an explanation for the pigment being present only in the tail, ears, face and legs of a Himalayan rabbit.
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(2)

(c)     Using the information given, explain why the phenotypes of rabbits with AABB and AA^hBB genotypes are the same.
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(2)(Total 9 marks)
Q9.          The shore crab is common in Britain. It lives both in the sea and in river estuaries, where it feeds on a wide variety of species.
(a)     The shore crab has recently spread to, and has established large populations in, the coastal waters of the USA, where it is not a native species. Explain how the shore crab has been able to establish large populations and why this is causing concern to ecologists in the USA.
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(5)

In Britain, crabs living in an estuary and along the neighbouring coast were studied. Crabs were collected from four different sites, A to D, as shown in the map.

The graph shows the mean water potential of the blood of samples of crabs from the four sites in relation to the water potential of the environment at the same sites. The isotonic line shows values at which the water potential of the blood and surrounding water would be the same.

(b)     Describe the relationship between the mean water potential of the blood of the crabs and the water potential of the surrounding water.
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S       (c)     Is there any net movement of water in or out of the blood of the crabs at sites A and B? Explain your answer.
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S       (d)     Crabs living at sites C and D actively transport salts into their blood through their gills.
(i)      Explain how this enables crabs to survive at these sites.
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(2)
(ii)     Crabs are unable to control their body temperature. In winter, when the water temperature falls, crab populations at sites C and D migrate towards the sea. Suggest the advantage of this behaviour.
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(3)
(Total 12 marks)
Q10.          In a sand dune succession the pioneer community (A) colonises bare sand. This community is replaced over time by other communities (B and C) until a climax community of woodland (D) is formed.

(a)     The communities A to D are composed of different species. Explain how the change in species composition occurs in a succession.
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(b)     Which community, A to D, is the most stable? Explain what makes this the most stable community.
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S       (c)     Many species in the pioneer community are xerophytes. Suggest and explain how having sunken stomata is an advantage to these plants.
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(3)

(d)     Explain why it would be more appropriate to use a transect rather than random quadrats when investigating this succession.
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(1)
(Total 9 marks)

 

Q11.          Lemmings are small mammals which live in the Arctic. Their main predator is the stoat, a small carnivorous mammal, which feeds almost entirely on lemmings. The graph shows the changes in the numbers of lemmings and stoats from 1988 to 2000.

(a)     Describe and explain the changes which occur in the lemming and stoat populations.
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S       (b)     Lemmings often live in isolated populations. From time to time some lemmings move and join other populations. Explain how this movement is important in maintaining genetic variability in lemming populations which have large fluctuations in size.
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S       (c)     James Bay is a large ocean bay in northern Canada. It was formed by the melting of glaciers. One species of lemming inhabits the eastern side of James Bay and another species of lemming inhabits the western side. Before the glaciers melted there was only one species of lemming present. Explain how two species of lemming evolved from the original species.
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Q12.          (a)     Explain what is meant by
(i)      succession;
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(ii)     a climax community.
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Heather plants are small shrubs. Heather plants are the dominant species in the climax community of some moorlands. The structure and shape of a heather plant changes as it ages. This results in changes in the species composition of the community. A large area of moorland was burnt leaving bare ground. The table shows four stages of succession in this area.

Time after burning / years

Appearance of
heather plant

Mean
percentage
cover of heather

Other plant species present

4 | | 10 | Many
12 | | 90 | Few
19 | | 75 | Several
24 | | 30 | Many
 
(b)     Explain why the number of other plant species decreases between 4 and 12 years after burning.
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(2)
S       (c)     The rate at which a heather plant produced new biomass was measured in g per kg of heather plant per year. This rate decreased as the plant aged. Use the information in the table to explain why.
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(Total 8 marks)
Q13.(a)     Explain one way in which the behaviour of chromosomes during meiosis produces genetic variation in gametes.
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(2)
(b)     In mosquitoes, the sex of an individual is determined by one gene. Males have the genotype Mm and females mm.
Another gene is carried on the same chromosome. Normal males and females are homozygous dd for this gene. Abnormal males have a dominant D allele.
The possible genotypes are shown below. The vertical lines represent homologous chromosomes.

During meiosis, allele D causes the homologous chromosome carrying the m allele to disintegrate. Cells lacking this chromosome do not develop further.
Complete the genetic diagram to show how allele D is transmitted from an abnormal male to his offspring.
 
| Parental phenotypes | Abnormal male | Normal female
| Parental genotypes | |
| Gametes | ....................... | .......................
| Offspring genotype(s) | ............................................................
| Offspring phenotype(s) | ............................................................

(3)(Total 5 marks)
Q14.          In the activated sludge method of sewage treatment, organic matter in untreated sewage supplies nutrients to bacteria in the treatment tank. These bacteria include decomposers and nitrifying bacteria. The bacteria are eaten by ciliated protoctistans, which are, in turn, eaten by carnivorous protoctistans.
(a)     (i)      Explain the roles of the decomposers and the nitrifying bacteria in converting nitrogen in organic compounds in the sewage into a soluble, inorganic form.
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(3)

(ii)     Nitrifying bacteria are one kind of bacteria that are important in the nitrogen cycle; nitrogen-fixing bacteria are another kind. Describe the part played by nitrogen-fixing bacteria in the nitrogen cycle.
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(2)

(b)     The organic matter in untreated sewage consists of small particles, which are suspended in water. Activated sludge consists of solid lumps (flocs) of organic matter and bacteria. When the two are mixed in the treatment tank, bacteria from the flocs become dispersed in the water and feed on the suspended organic matter, converting it to flocs. Different types of ciliated protoctistans feed on the bacteria.
•        Free-swimming protoctistans are able to move throughout the tank.
•        Crawling protoctistans can only move over the surface of the flocs.
The diagram shows the change in the nature of the organic matter in the treatment tank and the changes in the numbers of the different types of organisms present.

(i)      Explain the changes in the numbers of dispersed bacteria and the numbers of free-swimming protoctistans.
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(3)

(ii)     Explain how the changes that occur in the treatment tank illustrate the process of succession.
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(4)
(Total 12 marks)
Q15.(a)     The guinea pig, Cavia porcellus, is a small mammal. Complete the table to show the classification of the guinea pig.
 
| Kingdom |
| | Chordata
| | Mammalia
| | Rodentia
| Family | Caviidae
| Genus |
| Species |
(2)
(b)     In South America, there are several species of guinea pig. They are thought to have arisen by sympatric speciation.
Explain how sympatric speciation may have occurred.
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(3)

(c)     In guinea pigs, hair length and hair colour are controlled by two genes on different chromosomes. The hair may be either long or short and its colour either black or brown.
A male guinea pig and a female guinea pig both had short, black hair. The male was homozygous for hair length, and the female was homozygous for hair colour. Repeated crossings of these two guinea pigs resulted in offspring of four different genotypes, all of which had short, black hair.
Complete the genetic diagram to explain these results. Write in the box the symbols you will use to represent the alleles.
 
| Allele for short hair = ................. Allele for black hair = ................. | Allele for long hair = .................. Allele for brown hair = ...............

 
| Parental phenotypes | Male Short, black hair | Female Short, black hair
| Parental genotypes | .......................... | ..........................
| Gamete genotypes | .......................... | ..........................
| Offspring genotypes | ..........................................................
| Offspring phenotypes | Short, black hair

(4)
(d)     In another investigation, the same female guinea pig was twice mated with another male which had long, brown hair. Of the 14 offspring, 10 had short, black hair and 4 had long, black hair. The investigators expected equal numbers of offspring with these two phenotypes. They used a χ^2 test to determine whether the observed results fitted the expected 1:1 ratio.
Give a suitable null hypothesis for the investigation.
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(1)
(Total 10 marks)
Q16.          Snow geese fly north to the Arctic in the spring and form breeding colonies. Different colonies form at different latitudes. The greater the latitude, the further north is the colony. The further north a breeding colony forms, the colder the temperature and the greater the risk of snow.
(a)     There is a positive correlation between the size of snow geese and how far north they breed. A large size results in snow geese being adapted for breeding in colder conditions. Explain how.
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(2)

Snow geese are either white or blue in colour. The table shows the percentage of white snow geese in colonies at different latitudes at different times over a 40-year period. The blank cells in the table are years for which no figures are available.
 
Colony | Latitude in degrees north | Percentage of white snow geese each year
| | 1930 | 1950 | 1960 | 1970
A | 72 | 100 | | 100 | 100
B | 71 | | > 99 | > 99 | > 99
C | 66 | 95 | 85 | 76 |
D | 63 | 86 | 75 | 67 | 65
E | 55 | | 62 | | 28

(b)     (i)      Describe how the percentage of white snow geese varies with distance north.
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(1)

(ii)     The further north, the greater the risk of snow. Use this information to explain how natural selection might have accounted for the effect of latitude on the percentage of white snow geese.
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(3)
(c)     The percentage of white snow geese in these colonies changed over the period shown in the table. Use your knowledge of climate change to suggest an explanation.
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(2)
(d)     Snow geese breed in large colonies. Scientists studied the nests in one colony. For each nest, they recorded the day on which the first egg hatched. They also recorded the number of young that survived from the nest. They used the data to plot a graph.

(i)      What type of natural selection is shown in the graph?
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(ii)     Describe the evidence for your answer.
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(Total 10 marks)
Q17.          (a)     Succession occurs in natural ecosystems. Describe and explain how succession occurs.
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(b)     Changes in ecosystems can lead to speciation. In Southern California 10 000 years ago a number of interconnecting lakes contained a single species of pupfish. 
Increasing temperatures caused evaporation and the formation of separate, smaller lakes and streams. This led to the formation of a number of different species of pupfish. Explain how these different species evolved.
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Q18.          (a)     (i)      Explain what is meant by a recessive allele.
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(ii)     Explain what is meant by codominant alleles.
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(b)     The Rhesus blood group is genetically controlled. The gene for the Rhesus blood group has two alleles. The allele for Rhesus positive, R, is dominant to that for Rhesus negative, r. The diagram shows the inheritance of the Rhesus blood group in one family.

(i)      Explain one piece of evidence from the diagram which shows that the allele for Rhesus positive is dominant.
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(ii)     Explain one piece of evidence from the diagram which shows that the gene is not on the X chromosome.
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(c)     Sixteen percent of the population of Europe is Rhesus negative. Use the Hardy-Weinberg equation to calculate the percentage of this population that you would expect to be heterozygous for the Rhesus gene.
Show your working.

 

 
Answer .....................................................
(3)      (Total 9 marks)
Q19.Herbicides are substances that kill weeds. Three farmers wanted to know which herbicide to use to control weeds in fields of barley. They chose eleven fields of barley and used a different herbicide in each field. Four weeks later they collected, counted and weighed the weeds in each field. Their results are shown in Figure 1 and Figure 2.
Figure 1

Figure 2
 
(a)     Describe the difference in biomass of each of the weed plants in fields treated with herbicides G and H. Explain how you arrived at your answer.
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(b)     The farmers decided that K would be the best herbicide to use.
Explain why herbicide K would give a higher crop yield.
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(2)
(c)     The farmers carried out their investigation during the summer.
Suggest one advantage and one disadvantage of carrying out this investigation during the summer.
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(d)     One of the farmers told a local newspaper reporter of their findings. The newspaper published an article with the following headline: “Local farmers show scientists the way to bigger crop yields.” Was this headline justified? Explain your answer.
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(5)
(Total 11 marks)

Q20.          Scientists manufactured large quantities of human insulin using genetic engineering.
They started by isolating mRNA from pancreas cells. From this they produced DNA which coded for insulin.
(a)     (i)      Suggest two reasons why it was better to start with mRNA from pancreas cells rather than with the DNA from these cells.
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(ii)     The scientists used two enzymes, Enzyme 1 and Enzyme 2, to produce DNA from mRNA.
The reactions catalysed by these enzymes are shown below. 

Name enzymes 1 and 2.
Enzyme 1 .......................................................................................
Enzyme 2 .......................................................................................(2)

(iii)     In a double-stranded DNA molecule, the two strands are held together by weak bonds.
Name this type of bond.
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(b)     The scientists used the polymerase chain reaction (PCR) to make copies of the DNA.
The diagram shows the stages of the PCR.

(i)      P and Q are short lengths of  single-stranded DNA.
What name is given to molecules such as P and Q?
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(1)
(ii)     The mixture is cooled from 95°C to 55°C at step 2.
Explain why.
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(iii)     Explain the function of  molecules P and Q.
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(iv)    How many copies of  each original DNA molecule would be present after 5 cycles of  PCR?

(1)
(Total 10 marks)
 
Q21.          Scientists found a correlation between prostate cancer and exposure to cadmium ions.
The scientists investigated the effects of cadmium ions on cells from a human prostate gland.
They grew a culture of these cells in liquid growth medium and removed samples at intervals.
For each sample they measured
•    how much DNA was not methylated,
•    the activity of the enzyme methyltransferase.
Methyltransferase is an enzyme that adds methyl groups to some of the bases in DNA.
The addition of a methyl group is called methylation.

(a)     The scientists set up another culture as a control.
Describe how the scientists would have set up a control experiment for this investigation.
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(2)

(b)     Figures 1 and 2 show the scientists’ results.
Figure 1                                                                        Figure 2

(i)      The scientists expressed their results as percentages of the control values.
Suggest why.
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(1)

(ii)     Use information from Figure 1 to describe how exposure to cadmium ions affected the methylation of DNA.
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(1)

(iii)     Use information from Figure 2 to suggest what caused the change to the DNA shown in Figure 1.
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(1)
(c)     Prostate gland cells contain a tumour suppressor gene called p16.
During the investigation, the scientists also measured the amount of  p16 protein produced.
Figure 3 shows their results.
Figure 3

The scientists found that the promoter DNA of the p16 gene had become methylated. The promoter is the sequence of bases where the enzyme RNA-polymerase binds to a DNA molecule.
Explain how methylation of the promoter sequence of the p16 gene could cause the changes shown in Figure 3.
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(d)     Each week of the investigation, the scientists took samples of the cadmium-treated prostate cells from the laboratory cultures. They injected these cells into mice and monitored the mice for the growth of tumours.
It was only the samples taken in the tenth week that caused tumours to begin to grow in the mice.
Use information from Figures 1, 2 and 3 to suggest why.
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Q22.          (a)     Describe how a gene can be isolated from human DNA.
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(b)     Describe how an isolated gene can be replicated by the polymerase chain reaction (PCR).
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(4)

(c)     (i)      Describe how a harmless virus, genetically engineered to contain a CFTR gene, can be used to insert the gene into a cystic fibrosis sufferer.
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(2)

(ii)     A virus used in gene therapy has RNA as its genetic material and has an enzyme called reverse transcriptase. Inside a human cell, reverse transcriptase uses viral RNA to make viral DNA.
Explain why the enzyme is called reverse transcriptase.
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(1)(Total 9 marks)
Q23.          (a)     Plasmids can be modified by genetic engineering and inserted into bacteria. These bacteria can then make useful substances normally made by another organism. Explain how modified plasmids are made by genetic engineering and how the use of markers enable bacteria containing these plasmids to be detected.
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(6)
(b)     In gene therapy, genes are introduced into a person who has defective genes which do not produce an important substance. Three experiments were done to compare techniques for introducing an important substance into a person with defective genes.
1.   The substance was injected directly.
2.   Harmless viruses carrying genes coding for the substance were injected.
3.   The genes were put into a protein capsule which was inserted into the tissues.
The graph shows results of the experiments.

Takahiro Ochiya et al, Biomaterials for Gene Delivery: Studies on Metastasis, 
(National Cancer Centre, Research Institute, Tokyo, Japan) 1999

(i)      Describe the results of the three experiments.
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(3)

(ii)     Using the information in the graph, suggest one advantage and one disadvantage of the capsule method compared to the others.
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(2)
(Total 11 marks)

 

Q24.          One hypothesis for the cause of cancer of the colon (large intestine) is that Clostridium bacteria present in the gut can convert bile steroids into cancer-causing substances.
S       (a)     Explain the presence of bile in the colon.
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(2)

(b)     The concentrations of bile steroids and numbers of Clostridium bacteria were measured in people with colon cancer and in controls without colon cancer. The table shows the results.
 
Concentration of bile steroids | Number of Clostridium bacteria | Percentage of cancer patients | Percentage of controls | P

high
high
low
low

high
low
high
low

76
13
7
4

9
8
34
49

<0.01 <0.01 <0.01 <0.01

A statistical test showed there was a significant difference between the cancer patients and the controls in each of the four categories.
(i)      Explain how the results could be used to support the hypothesis that Clostridium bacteria convert bile steroids into substances which cause colon cancer.
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(ii)     Explain how the results indicate that other factors may be involved in causing colon cancer.
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(1)
S       (c)     Human cells contain genes that control their growth and division. One of these genes codes for a protein that prevents cell division. The substances formed from bile steroids by Clostridium bacteria may cause gene mutation. Describe and explain how these substances could cause colon cancer.
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(Total 9 marks)
Q25.          The polymerase chain reaction is a process which can be carried out in a laboratory to replicate DNA. The diagram shows the main stages involved in the polymerase chain reaction.

(a)     Explain why DNA is heated to 95 °C.
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(1)

(b)     What is the role of
(i)      a primer in this process;
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(1)

(ii)     DNA polymerase?
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(c)     (i)      How many DNA molecules will have been produced from one molecule of DNA after 6 complete cycles?
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(ii)     Suggest one use of the polymerase chain reaction.
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(d)     Give two ways in which the polymerase chain reaction differs from the process of transcription.
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(2)
(Total 7 marks)
Q26.          (a)     Cystic fibrosis can be caused by any one of several mutant alleles of the cystic fibrosis gene. The most common of these mutant alleles accounts for about 70% of cases of cystic fibrosis. The use of gene probes can identify individuals carrying this allele. Gene probes are single strands of DNA which are radioactively labelled. They have a base sequence that is complementary to a mutant allele. The main stages in using a gene probe are shown in the diagram.
 
Sample of DNA extracted from a person’s tissue and heated to separate the strands

↓

Radioactive gene probe added
to the DNA

↓
Excess probe washed away

↓
Sample tested for radioactivity

Using the information given, explain how the use of a gene probe could enable the presence of a mutant allele of the cystic fibrosis gene to be detected.
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(4)

(b)     Sheep have been genetically engineered to produce alpha-1-antitrypsin which is used to treat cystic fibrosis. Use your knowledge of this process to explain one argument for and one against using sheep in this way. 
For
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Against
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(2)
(Total 6 marks)

Q27.          (a)     An antigen in a vaccine leads to the production of antibodies. Describe the part played by B lymphocytes in this process.
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(4)

S       (b)     Hepatitis B vaccine contains a viral antigen produced by genetically modified bacteria. Describe how the isolated gene that codes for a protein in the virus’s coat could be transferred to the bacterial cells.
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Q28.          Read the following passage.
Malaria is a disease so deadly that it has devastated armies and destroyed great civilisations.
It has been estimated that in the course of history malaria has been responsible for the death
of one out of every two people who have ever lived. Even today, with all the advantages of
modern technology, it is still responsible for some three million deaths a year.
5     The first half of the twentieth century was a time of hope for malarial control. The drugs
chloroquine and proguanil had just been discovered and there seemed a real possibility of a
malaria-free world. Unfortunately, this honeymoon ended almost as soon as it had started,
with the emergence of drug-resistant parasite populations. Scientists now accept that whatever
new drug they come up with, it is likely to have a very limited effective life. As a result, they
10   are increasingly looking at combinations of drugs.
The approach to malaria control which holds the best hope is the production of a vaccine. One
of these is being developed by a researcher in South America. His vaccine is based on a small
synthetic polypeptide called SPf66 which is dissolved in a saline solution and given as an
injection. A series of early trials on human volunteers produced confusing results. In one trial
15   the effectiveness of the vaccine was claimed to be 80% while, in others, the results were
statistically insignificant. Not only were the results inconclusive but the methods used were
challenged by other scientists. In particular, the controls were considered inappropriate.
Another, possibly more promising, approach has been the development of a DNA-based
vaccine. In theory, all that is required is to identify the DNA from the parasite which encodes
20   key antigens. Unfortunately, scientists have hit snags. Although they have succeeded in
sequencing the human genome, the genome of the malarial parasite has created major
difficulties. This is partly because of the very high proportion of the bases adenine and
thymine. In some places these two bases average 80%, and on chromosomes 2 and 3 nearly
100% of the bases present are adenine and thymine. Because of this, it has proved impossible
25   to cut the relevant DNA with the commonly available restriction enzymes into pieces of a
suitable size for analysis.

          Use information from the passage and your own knowledge to answer the following questions.
(a)     Explain how a resistant parasite population is likely to arise and limit the life of any new anti-malarial drug (lines 8 - 9).
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(b)     A person has a 1 in 500 probability of being infected by a chloroquine-resistant strain of malarial parasite and a 1 in 500 probability of being infected by a proguanil-resistant strain. Use a calculation from these figures to explain why scientists are “increasingly looking at combinations of drugs” (lines 9 - 10).
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(c)     (i)      Explain why trials of the SPf66 vaccine needed a control.
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(1)
(ii)     The controls for the SPf66 vaccine trials were considered inappropriate (line 17).
Suggest how the control groups in these trials should have been treated.
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(2)
(d)     In some of the DNA of a malarial parasite, the proportion of adenine and thymine bases averages 80% (lines 22 - 23). In this DNA what percentage of the nucleotides would you expect to contain
(i)      phosphate; ..........................................................................................
(ii)     guanine? .............................................................................................
(2)
(e)     (i)      Use your knowledge of enzymes to explain why restriction enzymes only cut DNA at specific restriction sites.
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(3)
(ii)     Restriction enzymes that can cut the DNA of chromosomes 2 and 3 produce pieces that are too small for analysis. Explain why these restriction enzymes produce small DNA fragments.
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(2)
(Total 15 marks)

Q29.          Read the following passage.
In 1991, nine skeletons were found in Russia. They were believed to be those of Tsar Nicholas II, his family and staff who were killed in 1917 during the Russian revolution. Very small amounts of DNA were isolated from these skeletons. This DNA was used in the polymerase chain reaction (PCR). Genetic fingerprinting was then carried out on this DNA to identify the skeletons.
The chart shows some of the results obtained from the genetic fingerprinting of seven of the skeletons, three children and four adults.

Use information from the passage and your own knowledge to answer the following questions.
(a)     Explain why the polymerase chain reaction was used in this investigation.
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(2)

(b)     In the polymerase chain reaction, DNA is heated to 95 °C and nucleotides, enzymes and DNA primers are added to the mixture.
(i)      Explain why the DNA is heated to 95 °C.
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(1)

(ii)     What are DNA primers?
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(1)

(iii)     Why are DNA primers added during the polymerase chain reaction?
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(1)

(iv)    What is the advantage of the enzyme used in the polymerase chain reaction being thermostable?
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(2)

(c)     Describe how genetic fingerprinting is carried out.
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(6)

(d)     All three children on the chart had the same parents. One of the parents was Adult 1.
Which of the other three adults on the chart was the other parent? Give the reason for your answer.
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(Total 15 marks)
Q30.          Read the following passage.
Soon a single drop of blood might be enough to reveal, at a very early stage, if a patient has
cancer. It could also tell us what type of cancer it is and whether it is treatable. Fragments of
DNA from body cells are present in blood plasma. Some of these fragments may be from
cancer cells. The fragments can be detected by a new test in which a test strip containing
5     nucleic acid binds to sections of altered DNA.
Other cancer-detecting techniques involve removing a tissue sample from a patient. The
tissue sample is used to obtain mRNA. By examining the mRNA, scientists can discover 
whether cancer is present.
Use information from the passage and your own knowledge to answer the questions.
(a)     Describe how altered DNA may lead to cancer.
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(6)
(b)     Explain why fragments of DNA from cancer cells may be present in blood plasma 
(lines 3-4).
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(2)

(c)     Explain why the nucleic acid on the test strip will only bind to altered DNA (lines 4-5).
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(2)

(d)     This test strip will allow cancers to be detected at a very early stage. Explain why cancer is more likely to be treated successfully if the disease is detected at a very early stage.
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(2)

(e)     Explain how examining mRNA (line 7) enables scientists to discover whether cancer is present.
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(3)
(Total 15 marks)
Q31.          Read the following passage.
Shark-fin soup is an expensive delicacy. To provide the basic ingredient, fishermen catch the sharks, hack the fins off and throw the dead bodies back into the ocean. But sharks are slow to mature and produce only a few offspring at a time, so they are vulnerable to overfishing.
Monitoring the shark-fin trade is difficult, as once a fin has been cut off, it can be
5  extremely difficult to work out precisely from which species it was taken.
The DNA from different species of sharks shows some differences in base sequence. This has enabled a new genetic fingerprinting technique to be developed. This technique would allow conservationists and fisheries managers to assess which of the 400 shark species are most threatened by the trade in shark fins.
10   An identification process has been developed using a range of “primers”. These are short
pieces of single-stranded DNA that are complementary to a particular sequence of DNA.
Each primer is specific to the DNA of one shark species.
The primers are added to DNA taken from a shark’s fin and the polymerase chain reaction is carried out. Only two primers, one at each end of a certain piece of DNA, will bind. The piece
15   of DNA between the primers is replicated by the polymerase chain reaction. The primers that bind are specific to a particular species of shark and the length of the DNA fragment
replicated differs for each species. When this DNA is run in an electrophoresis gel it produces a single band, enabling the researchers to identify which species of shark is involved.
Use information from the passage and your own knowledge to answer the questions.
(a)     (i)      Explain why the DNA for each species of shark shows differences in base sequence (line 6).
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(2)

(ii)     Each primer is specific to the DNA of one shark species (line 12).
Explain why a particular primer will only bind to the DNA of one species.
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(2)

(iii)     The length of the replicated DNA fragment is different for each species.
Explain why this is important in identifying the shark species involved.
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(b)     In conventional DNA fingerprinting, a series of bands is produced on the electrophoresis gel, resembling the rungs of a ladder. When the DNA in this new genetic fingerprinting technique is run in an electrophoresis gel it produces just one of these ‘rungs’.
Explain the reason for the difference in the number of ‘rungs’ produced.
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(c)     Describe the polymerase chain reaction.
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(6)
(Total 15 marks)
Q32.          Read the following passage.
Herpes viruses cause cold sores and, in some cases, genital warts. Scientists are well
on the way to producing an antibody which will counteract herpes infection. This antibody works
by sticking to the virus and blocking its entry into cells. It has proved very effective in animal
tests.
5       One drawback with this approach, however, is that antibodies are at present produced using hamster ovary cells. This method is expensive and only produces limited amounts. A new technique is being developed to produce antibodies from plants. It involves introducing the DNA which codes for the required antibody into crop plants such as maize.
          Use information from the passage and your own knowledge to answer the questions.
(a)     (i)      What is an antibody?
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(ii)     Describe how antibodies are produced in the body following a viral infection.
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(b)     Describe how the antibody gene could be isolated from an animal cell and introduced into a crop plant such as maize (lines 7-8).
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(c)     Taking a course of these antibodies from plants to treat a herpes infection would not produce long-term protection against disease. Explain why.
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(d)     Explain one advantage of using antibodies from plants to treat a disease, rather than antibodies produced in an experimental animal (lines 5-6).
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(Total 15 marks)
Q33.          Read the following passage.
DNA tests were used to confirm the identity of deposed Iraqi leader Saddam Hussein, after his capture in December 2003. DNA tests were carried out to prove the suspect was not one of the many alleged “look alikes” of the former leader.
Firstly, the DNA was extracted from the mouth of the captured man using a swab. Great
5 	care was taken to check that the swab did not become contaminated with any other DNA. DNA extracted from the swab was then subjected to a standard technique called the polymerase chain reaction (PCR), which takes a couple of hours. Lastly, the sample was “typed” to give the genetic fingerprint. This was produced within 24 hours of Saddam Hussein’s capture. 
Tests for use in criminal cases often take much longer because samples are very small or
10      contaminated.It appears that Hussein’s genetic fingerprint was already stored away for comparison. This was
obtained from personal items such as his toothbrush. DNA from the toothbrush would have
been subjected to PCR before a DNA fingerprint could have been obtained.
Source: adapted from SHAONI BHATTACHARYA, New Scientist 15 December, 2003
          Use information from the passage and your own knowledge to answer the questions.
(a)     Describe how the technique of genetic fingerprinting is carried out and explain how it can be used to identify a person, such as Saddam Hussein.
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(6)

(b)     Explain how DNA could be present on a toothbrush (line 12).
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(2)

(c)     (i)      Explain why the polymerase chain reaction was used on the sample of DNA from the toothbrush (lines 12-13).
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(2)

(ii)     Explain one way in which the polymerase chain reaction differs from DNA replication in a cell.
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(d)     Tests for use in criminal cases often take much longer because samples are very small or contaminated (lines 8-10). Explain why it takes longer to obtain a genetic fingerprint if the sample is
(i)      very small;
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(ii)     contaminated.
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(Total 15 marks)
Q34.          Read the following passage.
The idea that bacteria could be used as a cancer treatment originated over 100 years
ago. A doctor noticed that some cancer patients with bacterial infections showed signs of recovery from the cancer. Attempts to use the bacteria as a treatment were
disappointing, however. Experiments showed that the bacteria made an impressive
5        onslaught on tumours, but a ring of cancerous tissue around the edge usually
survived.
Bacteria are once again being used in the war on cancer. Scientists have genetically
engineered a harmless strain of Clostridium to carry the gene for an enzyme. This
enzyme converts a harmless “prodrug” into an active drug which acts as a powerful
10      toxin. In people, this strain of Clostridium will only grow in tumours. Scientists hope
that when they inject the prodrug into a cancer patient’s blood, the bacteria will
convert it into an active drug. This will destroy tumours from the inside, leaving
healthy tissues unharmed.
The idea of converting a harmless prodrug into an active drug that only kills cancer
15      cells is not new. Apart from the use of genetically modified Clostridium, other
methods have been tried. One of these involved attaching an enzyme to an antibody
that binds only to cancer cells. This enzyme then activates the drug. Unfortunately,
different types of cancer require different antibodies, making the treatment expensive
to develop. Scientists hope their bacterial approach will offer a way of delivering the
20      enzymes to any cancer cell.
(a)     Describe how scientists could genetically engineer Clostridium bacteria to produce the enzyme which activates the prodrug. (lines 7-8)
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(6)
(b)     Explain why it is important to destroy all the cancer cells in a tumour.
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(2)
(c)     Explain how the use of antibodies (lines 16-17) results in a drug only killing cancer cells.
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(3)

(d)     Cancer drugs usually interfere with DNA replication. Use this information to explain why the cancer drugs are administered as prodrugs and not the active form.
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(4)
(Total 15 marks)

Q35.          Read the following passage.
The giant panda is one of the rarest animals in the world and is considered to be on the brink of extinction in the wild. Giant pandas have been kept and bred in zoos with the hope that they could be released into the wild. One worry is that small populations, like those in zoos, reduce the genetic variation needed to allow the species to
5        adapt to changing conditions. Unfortunately, pandas find it difficult to reproduce in captivity. Fertilisation of the females is guaranteed only by insemination with semen from several males. With so many potential fathers, the true paternity of the cubs is not clear. It is important to identify the fathers to maintain genetic variation.
10      Panda faeces can be collected in the wild. The faeces contain DNA from the panda, from the bamboo on which they feed and from bacteria. The DNA is subjected to the polymerase chain reaction (PCR). The primers used attach only to the panda DNA. The resulting DNA is subjected to genetic fingerprinting. This can help us to count the number of individuals in the wild because it allows us to identify individual pandas.

Use information in the passage and your own biological knowledge to answer the questions.

(a)     Describe how genetic fingerprinting may be carried out on a sample of panda DNA.
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(6)

(b)     (i)      Explain how genetic fingerprinting allows scientists to identify the father of a particular panda cub.
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(2)

(ii)     When pandas are bred in zoos, it is important to ensure only unrelated pandas breed. Suggest how genetic fingerprints might be used to do this.
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(1)

(c)     (i)      Suggest why panda DNA is found in faeces. (line 10)
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(1)
(ii)     Explain why the PCR is carried out on the DNA from the faeces. (line 12)
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(1)
(iii)     Explain why the primers used in the PCR will bind to panda DNA, but not to DNA from bacteria or bamboo. (line 12)
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(2)
(d)     DNA from wild pandas could also be obtained from blood samples. Suggest two advantages of using faeces, rather than blood samples, to obtain DNA from pandas.
1 ...................................................................................................................
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(2)
(Total 15 marks)