Author: Philip Colls
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Genetic diversity (selection and speciation) booklet   NAME:
Q1.
(a)     A student used a dilution series to investigate the number of cells present in a liquid culture of bacteria.
Describe how he made a 1 in 10 dilution and then used this to make a 1 in 1000 dilution of the original liquid culture of bacteria.
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(3)
(b)     Using an optical microscope, the student determined there were 15 cells in 0.004 mm^3 of the 1 in 1000 dilution of the culture.
Calculate the number of cells in 1 cm^3 of undiluted liquid culture.
Answer = ____________________ Number of cells
(2)

(c)     The student looked at cells in the 1 in 10 dilution during his preliminary work. He decided not to use this dilution to determine the number of cells in the undiluted liquid culture.
Suggest an explanation for the student’s decision.
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(d)     On some farms, animals are routinely given antibiotics in their food.
Scientists investigated whether these farm animals had antibiotic-resistant bacteria in their intestines. They tested the bacteria for resistance to two antibiotics, tetracycline and streptomycin.
Their results are shown in the table.
 
Antibiotic | Percentage of antibiotic-resistant bacteria
Tetracycline | 29
Streptomycin | 13
Suggest and explain one reason why bacteria resistant to tetracycline are more common than bacteria resistant to streptomycin in these farm animals.
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(e)     In recent years, these farm animals have not been given tetracycline in their food. Despite this, the percentage of bacteria resistant to tetracycline has remained constant.
Suggest one reason why.
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(1)
(Total 10 marks)
Q2.
The table shows the taxons and the names of the taxons used to classify one species of otter. They are not in the correct order.
 
| Taxon | Name of taxon
J | Family | Mustelidae
K | Kingdom | Animalia
L | Genus | Lutra
M | Class | Mammalia
N | Order | Carnivora
O | Phylum | Chordata
P | Domain | Eukarya
Q | Species | lutra
(a)     Put letters from the table above into the boxes in the correct order. Some boxes have been completed for you.
 
| | | | O | | M | | | | | | L | | Q
(1)
(b)     Give the scientific name of this otter.
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(1)

Scientists investigated the effect of hunting on the genetic diversity of otters. Otters are animals that were killed in very large numbers for their fur in the past.
The scientists obtained DNA from otters alive today and otters that were alive before hunting started.
For each sample of DNA, they recorded the number of base pairs in alleles of the same gene. Mutations change the numbers of base pairs over time.
The figure below shows the scientists’ results.

                        Allele size / number of base pairs
(c)     The scientists obtained DNA from otters that were alive before hunting started.
Suggest one source of this DNA.
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(1)
(d)     What can you conclude about the effect of hunting on genetic diversity in otters? Use data from the figure above to support your answer.
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(2)

(e)     Some populations of animals that have never been hunted show very low levels of genetic diversity. Other than hunting, suggest two reasons why populations might show very low levels of genetic diversity.
1. _________________________________________________________________
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2. _________________________________________________________________
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(Total 7 marks)
Q3. (a)     What is the name of a position of a gene on a chromosome?
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(b)     What is meant by genetic diversity?
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A geneticist investigated genetic diversity in four different breeds of dog. She compared DNA base sequences of the same genes from a large number of dogs from each breed.
The geneticist calculated the mean genetic diversity for each breed of dog. The value of this mean was between 0 and 1.
•        A mean value of 1 shows maximum genetic diversity.
•        A mean value of 0 shows no genetic diversity.
Her results are shown in the table
 
Breed of dog | Mean genetic diversity | Standard deviation
Airedale terrier | 0.51 | ± 0.03
Bull terrier | 0.38 | ± 0.02
Jack Russell terrier | 0.76 | ± 0.01
Miniature terrier | 0.47 | ± 0.02
(c)     What do these data show about the differences in genetic diversity between these breeds of dog?
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(d)     Miniature terriers were first bred from bull terriers in the 19th century.
Suggest one explanation for the observed difference in genetic diversity between miniature terriers and bull terriers.
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(Total 7 marks)
Q4.
 Sugar beet is a crop grown for the sugar stored in its root. The sugar is produced by photosynthesis in the leaves of the plant. Plant breeders selected high-yielding wild beet plants. They used these plants to produce a strain of sugar beet to grow as a crop.
The drawings show a wild beet plant and a sugar beet plant. The drawings are to the same scale.
 
(a)     Use the drawings to describe two ways in which a sugar beet plant is different from a wild beet plant.
Explain how each of these differences would give an increased yield of sugar.
Difference 1 _________________________________________________________
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Explanation _________________________________________________________
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Difference 2 _________________________________________________________
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Explanation _________________________________________________________
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(b)     Sugar beet plants have been selected for a faster rate of growth. Suggest how the faster rate of growth may increase profit for a farmer.
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(c)     Describe and explain how selection will have affected the genetic diversity of sugar beet.
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Q5. The Amazonian forest today contains a very high diversity of bird species.
•        Over the last 2 000 000 years, long periods of dry climate caused this forest to separate into a number of smaller forests.
•        Different plant communities developed in each of these smaller forests.
•        Each time the climate became wetter again, the smaller forests grew in size and merged to reform the Amazonian forest.
(a)     Use the information provided to explain how a very high diversity of bird species has developed in the Amazonian forest.

(5)
(b)     Speciation is far less frequent in the reformed Amazonian forest. Suggest one reason for this.
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Q6. Scientists investigated the presence of bacteria resistant to the antibiotic neomycin in turkeys, chickens and the farmers who kept the turkeys and chickens. They looked for Escherichia coli (E. coli) resistant to neomycin. At 46 farms, the scientists obtained samples of bacteria from faeces of turkeys, turkey farmers, chickens and chicken farmers. The turkey farmers very often used turkey food containing neomycin. The chicken farmers did not use chicken food containing neomycin very often.
The bacteria were grown on nutrient agar in cultures. The nutrient agar contained neomycin. Any resistant bacteria grew and divided to form visible colonies. The results are shown in the table
 
Samples taken from | Percentage of samples of faeces containing E. coli resistant to neomycin
Turkeys | 81
Turkeys farmers | 57
Chickens | 24
Chicken farmers | 8
(a)     Suggest two hypotheses the scientists were testing in this investigation.
Hypothesis 1 ________________________________________________________
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Hypothesis 2 ________________________________________________________
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(b)     (i)      Describe what the results in the table show.
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(ii)     Suggest and explain one reason for the observed differences in percentage of neomycin-resistant E. coli in turkeys and chickens.
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(c)     The scientists followed strict safety guidelines when collecting samples of faeces. Apart from the risk of contamination from E. coli this was especially important when collecting samples from humans. Explain why.
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(d)     Use the information provided to identify and explain one way in which the scientists increased the reliability of their method.
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(e)     Suggest how the scientists could use DNA to investigate whether the neomycin-resistant bacteria in farmers were identical to the strain of bacteria in the birds they kept.
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(f)     At one time, most animal feeds contained antibiotics that increased the rate of animal growth. In the UK, fewer animal feeds now contain antibiotics.
Suggest reasons why.
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___________________________________________________ (4) (Total 15 marks)
Q7. Some birds feed on animals found in mud in estuaries. The drawing shows the heads of three species of these birds and their prey.
 
(a)     Use the information in the drawing to explain how interspecific competition between the birds is reduced.
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(2)
(b)     Explain how competition might have played a part in the evolution of the long curved beak of the curlew.
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(4)

(c)     Mud higher up the shore receives fresh water draining from the land. Ragworms are able to survive in this mud because they can tolerate the absorption of water into their tissues. Explain what causes a ragworm to absorb water when higher up the shore.
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(2)
(Total 8 marks)
Q8.
The graph shows the variation in length of 86 Atlantic salmon.
 
(a)     Give two possible causes of this variation that result from meiosis during gamete formation.
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2. _________________________________________________________________
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(2)
(b)     When comparing variation in size between two groups of organisms, it is often considered more useful to compare standard deviations rather than ranges. Explain why.
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(2)
(Total 4 marks)
Q9. Figure 1 shows a fresh-water shrimp.
Figure 1
 
Biologists collected shrimps from a stream inside a cave and from the same stream when it was in the open. They measured the maximum diameter of each shrimp’s eye. They also measured the length of its antenna. From these measurements they calculated the mean values for each site. Figure 2 shows their results.
Figure 2
 
| Shrimps from the stream
| Inside the cave | In the open
Mean diameter of eye /mm | 0.09 | 0.24
Mean length of antenna /mm | 8.46 | 5.81
(a)     The biologists measured the maximum diameter of each shrimp’s eye. Explain why they measured the maximum diameter.
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(b)     A scientist working many years earlier suggested that animals which live in caves had similar adaptations. These adaptations included
•        smaller eyes
•        greater use of sense organs such as those involved in detecting touch.
(i)      Do the data in Figure 2 support this scientist’s suggestion? Explain your answer.
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(ii)     The data in Figure 2 are mean values. Explain how standard deviations of these cmean values would help you to interpret the data in Figure 2.
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(2)
(c)     The biologists investigated shrimps living in other streams. They measured the length of the antennae of these shrimps. They also measured their body length. Figure 3 shows the mean antenna length plotted against mean body length for each site.
Figure 3
 
(i)      What does the information in the graph suggest about the body lengths of shrimps living in caves and living in the open?
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(ii)     Do the data in the graph support the conclusion that shrimps with longer bodies have longer antennae? Give the reason for your answer.
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(1)
Other biologists investigated the genetic diversity of these shrimps. Figure 4 shows some of the data they collected.
Figure 4
 
Gene | Allele | Percentage of shrimps with this allele in steam
| | Inside a cave | In the open
PGI | A | 0.9 | 2.5
| B | 0.0 | 3.3
| C | 98.2 | 66.4
| D | 0.9 | 6.6
| E | 0.0 | 21.3
ACO2 | J | 0.0 | 5.6
| K | 0.0 | 76.7
| L | 100.0 | 17.8
(d)     The biologists concluded that the shrimps in the open had a higher genetic diversity than those in the cave. Explain how the data in Figure 4 support this conclusion.
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(1)
(e)     The percentage of shrimps with allele L in the cave is different from the percentage of shrimps with allele L in the open. Use your knowledge of the founder effect to suggest a reason for this difference.
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(3)

(f)      The biologists who studied these shrimps wanted to know if the shrimps living in the cave were the same species as those living in the open. They used breeding experiments to investigate this.
(i)      Describe how the biologists should carry out these breeding experiments.
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(ii)     The results of breeding experiments would help the biologists to decide whether the shrimps were the same species. Explain how.
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(3)
(Total 15 marks)
 
Q10. Lake Malawi in East Africa contains around 400 different species of cichlids which are small, brightly coloured fish. All these species have evolved from a common ancestor.
(a)     Describe one way in which scientists could find out whether cichlids from two different populations belong to the same species.
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(b)     During the last 700 000 years there have been long periods when the water level was much lower and Lake Malawi split up into many smaller lakes. Explain how speciation of the cichlids may have occurred following the formation of separate, smaller lakes.
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(c)     Many species of cichlids are similar in size and, apart from their colour, in appearance. Suggest how the variety of colour patterns displayed by these cichlids may help to maintain the fish as separate species.
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(2)
(Total 8 marks)
Q11.
A student investigated the effect of three types of disinfectant on the growth of Lactobacillus bacteria.
During the investigation, the student:
•   boiled the agar before pouring the agar plates
•   transferred 0.5 cm^3 of a diluted liquid culture of Lactobacillus onto each agar plate
•   left some agar plates as controls
•   added to other agar plates different concentrations of the disinfectants as shown in the table in part (a).
After 2 days, she counted the number of colonies of bacteria on each agar plate.
(a)     Explain the purpose of:
boiling the agar ______________________________________________________
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transferring the same volume of liquid culture onto each agar plate.
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(2)

The three disinfectants used by the student were Lysol, propan-2-ol and ammonia.
The table shows the student’s results.
 
Concentration of disinfectant / arbitrary units | Number of colonies of bacteria
| Lysol | Propan-2-ol | Ammonia
0 | 300 | 300 | 300
5 | 0 | 290 | 300
10 | 0 | 195 | 295
15 | 0 | 0 | 275
20 | 0 | 0 | 240
The liquid culture the student transferred was diluted by 1 in 10 000 (10^−4).
(b)     Use information in this question to calculate how many bacteria were present in 1 cm^3 of undiluted liquid culture.
Answer = ____________________
(2)
(c)     The student concluded that the minimum concentration of propan-2-ol needed to stop the growth of Lactobacillus was 15 units. This conclusion is incorrect.
Describe how you could obtain a more accurate estimate of the minimum concentration of propan-2-ol needed to stop the growth of this species of bacterium.
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(2)
(Total 6 marks)

Q12.
Scientists investigated treatment of a human bladder infection caused by a species of bacterium. This species of bacterium is often resistant to the antibiotics currently used for treatment.
They investigated the use of a new antibiotic to treat the bladder infection. The new antibiotic inhibits the bacterial ATP synthase enzyme.
(a)     Place a tick (✔) in the appropriate box next to the equation which represents the reaction catalysed by ATP synthase.
 
ATP ⟶ ADP + P_i + H_2O |
ATP + H_2O ⟶ ADP + P_i |
ADP + P_i ⟶ ATP + H_2O |
ADP + P_i + H_2O ⟶ ATP |
(1)
(b)     The new antibiotic is safe to use in humans because it does not inhibit the ATP synthase found in human cells.
Suggest why human ATP synthase is not inhibited and bacterial synthase is inhibited.
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(1)
(c)     The scientists tested the new antibiotic on mice with the same bladder infection. They divided these mice into three groups, C, R and A.
•   Group C was the control (untreated).
•   Group R was treated with an antibiotic currently used against this bladder infection.
•   Group A was treated with the new antibiotic.
They removed samples from the bladder of these mice after treatment and estimated the total number of bacteria in the bladder.
Their results are shown in the graph.
 
The antibiotics were given to the mice at a dose of 25 mg kg^−1 per day. Calculate how much antibiotic would be given to a 30 g mouse each day. Show your working.
Answer = ____________________ mg
(2)
(d)     Calculate the percentage difference in actual numbers of bacteria in group A compared with group R. The actual number of bacteria can be calculated from the log_10 value by using the 10^x function on a calculator.
Show your working.
Answer = ____________________ %
(2)
(e)     The scientists suggested that people newly diagnosed with this bladder infection should be treated with both the current antibiotic and the new antibiotic.
Explain why the scientists made this suggestion.
Use information from the graph in part (c) and your knowledge of evolution of antibiotic resistance in bacteria in your answer.
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(3)
(Total 9 marks)

Mark schemes
Q1.
(a)     1.      Add 1 part (bacteria) culture to 9 parts (sterile) liquid (to make 10^–1 dilution);
Accept water / nutrient / broth for liquid
2.      Mix (well);
Accept stir
3.      Repeat using 9 parts fresh (sterile) liquid and 1 part of 10^–1 and 10^–2 dilutions to make 10^–3 dilution;
OR
Add 1 part 10^–1 (suspension) to 99 parts (sterile) liquid (to make 10^–3 dilution);
Accept water / nutrient / broth for liquid
Reject 1 part (undiluted) culture added to 999 parts liquid
3
(b)     3.75 × 10^9 / 3 750 000 000;;
Accept for 1 mark: 3750 000 / 3.75 × 10^6 (cells per mm^3)
OR
3.75 × 10^12 (wrong volume conversion)
OR
3750 (cells per mm^3 of diluted culture)
OR
Evidence of using correct dilution conversion and correct volume conversion, i.e., × 1000 and × 1000
2
(c)     1.      Count unlikely to be accurate / repeatable / reproducible / reliable;
2.      Because too many cells;
OR
Because cells overlapping / not spread out;
2
(d)     1.      Tetracycline used more often / in higher doses;
2.      Resistant bacteria more likely to (survive and reproduce and) pass on allele/gene for (tetracycline) resistance;
OR
3.      More / higher frequency of mutations (for tetracycline resistance);
Reject reference to mutation being caused by use of antibiotic
4.      (so) gene passed on to more bacteria;
OR
5.      Tetracycline used over longer time period;
6.      More time for (chance) mutation to occur / for selection to occur;
Ignore reference to resistant animals
Ignore reference to immunity
2
(e)     No selection against resistant bacteria / resistance gene/allele;
OR
Bacteria pass on (resistance) gene / allele when they reproduce;
OR
Bacteria resistant to tetracycline are passed on from one generation of farm animals to the next (probably via faeces);
OR
Environment does not change, so stabilising selection occurs;
Accept no selection to get rid of it
Reject reference to mitosis or immunity
1
[10]
Q2.
(a)      PKNJ.
1
(b)     Lutra lutra.
1
(c)     Bone / skin / preserved remains / museums.
1
(d)     1.      (Hunting) reduced population size(s), so (much) only few alleles left;
Accept bottleneck
2.      Otters today from one / few surviving population(s);
Accept founder effect
3.      Inbreeding.
Allow any two
2 max
(e)     1.      Population might have been very small / genetic bottleneck;
2.      Population might have started with small number of individuals / by one pregnant female / founder effect;
3.      Inbreeding.
Allow any two
2 max
[7]
Q3.
(a)     Locus;
Accept: loci
1
(b)     Differences in DNA / differences in base sequence of DNA;
Accept: number of different alleles / size/variation in gene pool
Reject: genes
1
(c)     1.      Jack Russell (genetic) diversity is (significantly) greatest;
2.      Bull terrier (genetic) diversity is (significantly) smallest / is most inbred;
3.      Miniature terrier and Airedale terriers are similar;
1-3: do not credit just a list of values
4.       Standard deviations do not overlap / do overlap with correct ref to significance;
Reference to significance must be relevant to examples given
Max 3
(d)     1.      (Bull terrier) breeding has included a genetic bottleneck/ small population/more inbreeding/ greater selection (pressure);
Accept: founder effect
2.      Reduced number of different alleles/size of gene pool;
Reject: decrease in number of genes
Ignore ref to mutations
OR
3.      Miniature (terrier) breeding has included more outbreeding/less selection (pressure);
4.      Increased number of different alleles/larger gene pool/more variety of alleles;
Reject if genes used instead of alleles
Reject: lower frequency of alleles
Ignore ref to mutations
2
[7]
Q4.
(a)     2 of the following pairs:
Mark for explanation must be paired with correct change in structure
1.      Larger leaves;
2.      Photosynthesis;
OR
Accept converse descriptions of leaves, root and stem: longer root, taller stem, smaller leaves
3.      Larger / bigger / thicker root;
4.      Storage;
OR
5.      Stem shorter / absent;
Accept converse correct explanation
6.      Less energy used in stem growth / more energy for producing sugar;
4 max
(b)     Beet ready quicker / less time required / allows land to be used again / harvested earlier;
Allow more crops / many harvests. Ignore references to yield / profit
1
(c)     1.      (Diversity) reduced / fewer different alleles / less variation / smaller gene pool;
2.      As alleles have been chosen / rejected;
2
[7]
Q5.
(a)     1.      No interbreeding / gene pools are separate / geographic(al) isolation;
Accept: all marks if answer written in context of producing increased diversity of plants
1 Do not award this mark in context of new species being formed and then not interbreeding
1 Accept reproductive isolation as an alternative to no interbreeding
2.      Mutation;
2 Accept: genetic variation
3.      Different selection pressures / different foods / niches / habitats;
3 Accept: different environment / biotic / abiotic conditions or named condition
3 Neutral: different climates
4.      Adapted organisms survive and breed / differential reproductive success;
5.      Change / increase in allele frequency / frequencies;
5
(b)     Similar / same environmental / abiotic / biotic factors / similar / same selection pressures / no isolation / gene flow can occur (within a species);
Accept: same environment
1
[6]
Q6.
(a)     1.      Type of feed affects (antibiotic) resistant bacteria (in animals);
Accept: null hypotheses
Accept predictions, for example
More antibiotic resistant bacteria form in animals fed with antibiotics in their food
2.      (Antibiotic) resistant resistant infect /are passed on to animals/farmer / resistant resistant are passed between animals;
Accept: bird to bird/bird to human/human to human
Accept: a link (exists) between (antibiotic) resistance in animals and their keepers/farmers – as lowest level QWC
3.      Incidence of (antibiotic) resistant resistant differs in chickens and turkeys;
Accept: a comparison, eg ‘more resistant bacteria in chickens than turkeys'
4.      Incidence of (antibiotic) resistant resistant differs in chicken farmers and turkey farmers;
Accept: a comparison, eg ‘more resistant bacteria in chickens than turkeys'
Max 2
(b)     (i)      1.      Large(r) percentage of resistant bacteria in turkeys/low(er) percentage of resistant bacteria in chickens;
Accept: E coli for bacteria
Ignore: number, eg. ignore ‘more’/’fewer’ turkeys/chickens
2.      Large(r) percentage of resistant bacteria in turkey farmers/low(er) percentage of resistant bacteria in chicken farmers;
2
(ii)     1.      (More) antibiotic in turkey feed kills (more) non-resistant bacteria / resistant bacteria survive;
Accept: antibiotic creates selection pressure
Survive must be explicit, not implied by ‘reproduce’
2.      (Resistant bacteria) reproduce / pass on gene for resistance;
2
(c)     (Human) faeces contain pathogens;
Accept: harmful organisms
1
(d)     1.      Large number of farms / farmers (surveyed) / 46;
‘Reliable’ is used in the question stem
2.      So results are (likely to be) representative / can identify anomalous results;
Ignore: reproducible / accurate / valid / reliable
Accept valid explanation of replicates minimising effects of chance
2
(e)     1.      (DNA) hybridisation (of gene for resistance in bacteria taken from bird and farmer);
2.      (Identical) strands separate at high(est) temperature;
OR
3.      Compare base/nucleotide sequence (of gene for resistance in bacteria taken from bird and farmer);
4.      (Identical strains) have identical/same base sequences
Mark in pairs, do not mix and match.
Accept: bacteria in bird and farmer/both types of bacteria have identical base sequences = 2 marks
2
(f)      1.      (Antibiotic use has) increased cases of bacterial resistance;
Accept: number
2.      Transfer/horizontal transmission of (resistance) gene to pathogens/harmful bacteria;
Accept: conjugation
3.      (Antibiotic) resistant bacteria cause harm / medical treatments less effective;
Accept: superbug
4.      Avoids side effects on animals;
5.      Increased demand for organic food;
6.      Antibiotic/resistant bacteria could be present in human food;
7.      High cost of antibiotics;
8.      Legislation has controlled antibiotic use;
Accept: EU/government guidelines
4 max
[15]
Q7.
(a)     description of interspecific competition / competition between species / birds with beaks of different lengths;
link length of beaks to different positions of prey / reference to named bird with particular prey e.g. curlews with longer beaks able to feed on ragworms;
2
(b)     variation in beak length in curlews / one species;
longer / more curved beaked curlews outcompete / at advantage / 
suggested advantage e.g. larger / curled beaks access more food;
reproduction;
genes passed on (to offspring);
4
(c)     body has lower water potential;
water diffuses along a water potential gradient / by osmosis;
2
[8]
Q8.
(a)     (i)     Continuous variation – range of values / not discrete categories / many
categories / no gaps;
1
(ii)     Crossing over / chiasmata;
Random segregation / independent assortment;
In meiosis I and meiosis II;
max 2
(b)     Range influenced by single ‘outlier’ (accept anomaly) / 
converse for S.D.;
S.D. shows dispersion / spread about mean / range only shows highest
and lowest values / extremes;
Or
S.D. allows statistical use;
Tests whether or not differences are significant;
max 2
[4]
Q9.
(a)     (So results) can be compared / so measurement is the same each time / because eye is not perfectly round / uniform;
Accept eye opens to different amounts
1
(b)     (i)      1.      Eye (diameter) is smaller and antennae longer;
2.      Antennae detecting touch;
3.      Data only refers to shrimps / data may not apply to all animals / only in one area;
The principle here is that candidate has recognised that both features confirm suggestion. Exact wording does not matter.
2 max
(ii)     1.      Standard deviation gives a measure of spread / variation;
2.      More standard deviations overlap, the less likely it is that differences are real / significant / the more likely they are caused by chance;
Do not accept range
Accept converse.
Although we are looking for the idea of significance, we cannot require this term.
2
(c)     (i)      Qualitative statement about
          difference in size / 
          difference in variation / 
          overlap in size;
Quantitative statement about
          difference in size / 
          difference in variation / 
          overlap in size;
Supported by relevant two sets of figures from graph;;
Note simplistic answer involving a quantitative statement gains 1 mark.
More specific answer involving quantitative information gains 2 marks.
2
(ii)     (No) for same body length, antenna are longer / antenna are shorter / some with longer body have short antennae / some with shorter body length have longer antennae;
OR
(Yes) positive correlation in open / in cave;
Habitat not critical as a term.
Must refer to idea of same habitat
Accept description
1
(d)     More alleles of each gene / shrimps in open have all the alleles;
Candidates are required to use the information from the table. Must therefore refer to alleles.
1
(e)     1.      A small number of shrimps were / went into the cave;
2.      All / high proportion of shrimps had allele L;
3.      Cave population descended from these / these reproduce;
3
(f)      (i)      1.      Cross shrimps from two sites / watch courtship;
2.      Breed young together / observe mating;
3.      Allow 1 mark for any method of improving quality of results e.g. carry out reciprocal crosses / large number of crosses / isolate beforehand;
Other valid equivalent suggestions should be accepted.
(ii)     If same species the shrimps would breed, producing fertile young / courtship species specific;
Accept any form of evidence – mating / laying eggs / giving birth to young.
3
[15]
Q10.
(a)     breed together;
if fertile offspring, then same species;
2
(b)     isolation of two populations;
variation already present due to mutations;
different environmental conditions / selection pressures leading to
selection of different features and hence different alleles;
different frequency of alleles;
separate gene pools / no interbreeding;
4
(c)     selection of mate dependent on colour pattern;
prevents interbreeding / keeps gene pools separate;
2
[8]
Q11.
(a)     1.      So no contamination / other bacteria;
2.      So same number of bacteria transferred to allow comparison;
1.      Accept sterilisation / kills all (bacteria)
2.      Allow amount / concentration for number
2
(b)     6 000 000
OR
6 × 10 ^6;
1 mark for 3 000 000
OR
3 × 10 ^6
Allow 1 mark for 600 (in 1cm ^3 of diluted culture)
2
(c)     1.      (Several) values between 10 and 15 (units);
2.      Repetitions of each;
1.      Accept descriptions of this
Ignore repeat the investigation / repeat at 10 and 15 units.
2
[6]
Q12.
(a) 
ATP ⟶ ADP + P_i + H_2O |
ATP + H_2O ⟶ ADP + P_i |
ADP + P_i ⟶ ATP + H_2O |
ADP + P_i + H_2O ⟶ ATP |
1
(b)     1.      Human ATP synthase has a different tertiary structure to bacterial ATP synthase
OR
Human ATP synthase has a different shape active site to bacterial ATP synthase
OR
Antibiotic cannot enter human cells/mitochondria
OR
Antibiotic not complementary (to human ATP synthase);
1
(c)     0.75;
One mark for showing 30 g = 0.03 kg;
One mark for showing 0.025 mg g^−1
2
(d)     Answer in range 97.0 − 97.8%;
OR
Answer in range 3288 − 4368%;
2.      1 mark for correct log_10 readings from graph converted to actual numbers
(16.98 − 19.50 and 660.7 − 758.6)
2
(e)     1.      (From the graph in part c) New / old antibiotic does not kill all bacteria;
OR
(From the graph in part c) Some bacteria are resistant to the new / old antibiotic;
2.      Resistant bacteria will reproduce to produce (more) resistant bacteria;
3.      (Use of both) one antibiotic will kill bacteria resistant to the other antibiotic;
OR
Unlikely that bacteria are resistant to both the new and the old antibiotic;
OR
Use of both antibiotics (likely to) kill all / most bacteria;
Accept use of ‘A’ for ‘new antibiotic’ and ‘R’ for ‘old antibiotic’.
1.      Must relate to the bacteria that are still present – ‘some bacteria are killed’ or ‘the bacteria number is reduced ’ is insufficient.
2.      Accept ‘resistant bacteria reproduce to pass on resistance gene / allele’
3.      ‘Use of both antibiotics will be more effective’ is insufficient.
3
[9]