Author: Philip Colls
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Speciation and succession Booklet revision questions   NAME:
Q1.
Ecologists investigated the size of an insect population on a small island. They used a mark-release-recapture method. To mark the insects they used a fluorescent powder. This powder glows bright red when exposed to ultraviolet (UV) light.
(a)     The ecologists captured insects from a number of sites on the island. Suggest how they decided where to take their samples.
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(b)     Give two assumptions made when using the mark-release-recapture method.
1. _________________________________________________________________
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2. _________________________________________________________________
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(c)     Suggest the advantage of using the fluorescent powder in this experiment.
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(2)

The ecologists did not release any of the insects they captured 1–5 days after release of the marked insects.
The table below shows the ecologists’ results.

Days after 
release

Number of marked 
insects remaining
in population

Number of insects
captured

Number of 
captured insects 
that were marked

1 | 1508 | 524 | 78
2 | 1430 | 421 | 30
3 | 1400 | 418 | 18
4 | 1382 | 284 | 2
5 | 1380 | 232 | 9
(d)     Calculate the number of insects on this island 1 day after release of the marked insects.
Show your working.

 
Answer = ____________________
(2)
(e)     The ecologists expected to obtain the same result from their calculations of the number of insects on this island on each day during the period 1–5 days after release. In fact, their estimated number increased after day 1.
During the same period, the number of insects they caught decreased.
The method used by the ecologists might have caused these changes.
Use the information provided to suggest one way in which the method used by the ecologists might have caused the increase in their estimates of the size of the insect population.
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(2)
(Total 10 marks)
Q2. There are nine subspecies of giraffe. These subspecies evolved when populations of giraffe were separated for long time periods. Each subspecies has distinct coloured skin markings. Some biologists have suggested that up to six of these subspecies should be classified as different species.
(a)     Explain how different subspecies of giraffe may have evolved from a common ancestor. Use information from the passage in your answer.
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(b)     Biologists compared the mitochondrial DNA of the different subspecies of giraffe. They used the results from comparing this DNA to conclude that six of the nine subspecies are separate species.
Suggest how they came to this conclusion.
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(Total 7 marks)
Q3.
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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 (2) (Total 8 marks)
Q4. Malaria is a disease caused by a parasite. Scientists investigated the effect of malaria on competition between two species of Anolis lizard on a small Caribbean island. They sampled both populations by collecting lizards from a large number of sites on the island.
(a)     (i)       Explain the importance of collecting lizards from a large number of sites.
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(ii)     Describe one method the scientists could have used to ensure that the sites were chosen without bias.
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(iii)    The population number of both species of lizard varied at different times of the year. Suggest two reasons why.
1. ____________________________________________________________
2. __________________________________________________________ (2)
The scientists investigated the percentage of lizards of both species that were infected with malaria at different sites on the island. They collected samples of both lizards at intervals of 3 months for 1 year. They also recorded the elevation (height above sea level) of each site. Some of their results are shown in the table.

Site

Elevation of
collection
site /
metres

Total number
of
A. gingivinus
collected in
one year

Percentage of
A. gingivinus
infected with
malaria

Total number
of
A. wattsi
collected in
one year

Percentage of
A. wattsi
infected with
malaria

1 | 10 | 13 | 0 | 0 | 0
2 | 80 | 30 | 0 | 0 | 0
3 | 120 | 35 | 23 | 3 | 0
4 | 200 | 40 | 30 | 7 | 0
5 | 300 | 52 | 46 | 12 | 0
6 | 315 | 35 | 31 | 13 | 1
7 | 370 | 155 | 37 | 79 | 2
8 | 414 | 124 | 44 | 68 | 4
(b)     When analysing their results, the scientists used the percentage of lizards infected at each site, rather than the number of lizards infected. Explain why.
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(c)     A preliminary study suggested that malarial infections were more common at higher elevations. Use the information provided to evaluate this suggestion.
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(d)    (i)      As a result of this investigation, the scientists concluded that the presence of malaria provided a competitive advantage to A. wattsi. Use the information provided to explain how they reached this conclusion.
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(ii)     The malarial parasite of Anolis lizards destroys both red and white blood cells.Suggest how an increase in the percentage of A. gingivinus infected with malaria could result in A.wattsi having a competitive advantage.
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(2)
(iii)    The scientists carried out a statistical test to determine whether the correlation between the number of A. wattsi collected and the percentage of A. gingivinus infected was significant. They obtained a value for P of < 0.01.
Use the terms probability and chance to help explain what this means.
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Q5. Shrews are small mammals. Three species of shrew live in mainland Britain. The table shows some features of these shrews.

Species

Mean body
mass / g

Mean length of head and
body / mm

Food

Common shrew | 10 | 79 | Mainly insects and
Pygmy shrew | 5 | 58 | other small
Water shrew | 13 | 85 | invertebrates
A team of biologists investigated a method of estimating the abundance of shrews. They used plastic tubes, called hair tubes. Some of the hairs from a shrew that enters one of these tubes stick to glue in the tube. These hairs can be used to identify the species of shrew. The diagram shows a set of these hair tubes.
 
(a)     (i)      Faunagoo is a glue that remains sticky after wetting and drying. Explain the advantage of using Faunagoo in these hair tubes.
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(ii)     The diagram shows that the biologists partly blocked the entrances to the tubes with tape. Suggest why they partly blocked the entrances.
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(b)     The biologists needed to find a way of distinguishing between the hairs of the three species of shrew. They collected hairs from shrews of each species. For each species, they selected hairs at random and made different measurements.
Explain why the biologists selected the hairs at random.
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(c)     Repeatable measurements are measurements of the same feature that are very similar.
In this investigation, each measurement was made by two observers. This helped the team to check the repeatability of these measurements.
(i)      Explain why it was important to check the repeatability of the measurements.
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(ii)     You could use a scatter diagram to check the repeatability of measurements made by two observers. Describe how.
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(d)     The biologists used hair tubes to find the abundance of shrews along the edges of some fields. They also used traps that caught shrews without harming them. They selected areas where all three species of shrew were present.
•        They put sets of hair tubes at 5 m intervals along the edges of the fields. They inspected the tubes one week later and recorded the number of sets of tubes that contained shrew hairs. They called this the hair tube index.
•        At each site where they used hair tubes, they set traps immediately after using the hair tubes. They recorded the number of different shrews caught in these traps.
(i)      The research team found the hair tube index. Explain why they could not use the hair tubes to find the total number of shrews present.
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(ii)     The research team set the traps immediately after using the hair tubes. Explain why setting the traps immediately after using the hair tubes would make comparisons between the two methods more reliable.
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(2)
The graphs are types of scatter diagram called bubble plots. They show hair tube index plotted against the number of shrews caught in traps. The area of the bubble is proportional to the number of records plotted.

(e)     Explain why a statistical test was necessary in analysing the results for the common shrew. Use the terms chance and probability in your answer.
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(f)      (i)      The biologists concluded that hair tubes were a reliable way of measuring the abundance of common shrews. Give evidence from the graph to support this conclusion.
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(ii)     Use information in this question to evaluate the use of hair tubes as a way of measuring the abundance of pygmy shrews.
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Q6. 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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(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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(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)

Q7.
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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(2)
(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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(c)     The farmers carried out their investigation during the summer.
Suggest one advantage and one disadvantage of carrying out this investigation during the summer.
Advantage __________________________________________________________
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Disadvantage________________________________________________________
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(2)
(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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Q8.
When coal is mined by open-cast mining, the top layer of soil is first scraped off and stored in a large heap. Once mining has finished, the area can be reclaimed. Soil from this store is then spread back over the surface.
Some of the bacteria living in the soil store respire aerobically and some respire anaerobically. Table 1 shows the numbers of aerobic and anaerobic bacteria found at different depths in a soil store.
 
Depth / cm | Mean number of bacteria per gram of soil (× 10^7)
| Aerobic bacteria | Anaerobic bacteria
| after 1 month | after 6 months | after 1 month | after 6 months
0 | 12.0 | 12.1 | 0.6 | 0.8
50 | 10.4 | 8.6 | 0.8 | 1.3
100 | 10.1 | 6.1 | 0.7 | 4.1
150 | 10.0 | 3.2 | 0.7 | 7.9
200 | 11.6 | 0.8 | 0.7 | 8.4
250 | 11.9 | 0.7 | 0.8 | 8.8
300 | 11.0 | 0.8 | 0.6 | 9.1
Table 1
(a)     Some of the soil used to determine bacterial numbers was collected from the surface of the soil store. Describe how you would ensure that this soil was collected at random.
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(2)
(b)     (i)      Describe how the numbers of aerobic bacteria after 6 months change with depth.
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(ii)     Explain the difference in the numbers of aerobic bacteria at a depth of 300 cm between 1 and 6 months.
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(c)     Explain how the changes in bacterial numbers which take place at 150 cm illustrate the process of succession.
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(3)
Dehydrogenase is an enzyme involved in aerobic respiration. Dehydrogenase activity in a soil sample can be used as a measure of the activity of aerobic bacteria. The graph shows the mean dehydrogenase activity of soil samples taken from the same depth in a soil store at different times. The bars on the graph represent two standard errors above and below the mean.

(d)     (i)      From what depth in the soil store would you expect these soil samples to have been taken? Use information from Table 1 to explain your answer.
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(ii)     How would you expect dehydrogenase activity to vary with depth after 6 months? Use information from Table 1 to explain your answer.
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(e)     What do the error bars tell you about the difference between the mean dehydrogenase activity at 6 months and 3 years? Explain your answer in terms of probability and chance.
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(f)      Table 2 shows the dehydrogenase activity and the number of aerobic bacteria present in some soil samples.
 
Dehydrogenase activity / arbitrary units | Number of aerobic bacteria per gram of soil (× 10^7)
13.1 | 12.0
9.2 | 8.7
5.5 | 6.5
3.0 | 4.6
2.2 | 2.7
0.4 | 0.6
Table 2
A sample of soil was found to have dehydrogenase activity of 8.7 arbitrary units. Explain how you would use the data in Table 2 to predict the likely number of aerobic bacteria in 1 g of this soil sample.
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(3)
(Total 20 marks)

Mark schemes
Q1.
(a)     1.      Draw grid over (map of) area;
2.      Select squares / coordinates at random.
2
(b)     1.      No emigration / immigration;
2.      No losses to predation;
3.      Marking does not affect survival;
4.      Birth rate and death rate equal;
5.      (In this case) all belong to one population.
2 max
(c)     1.      Only glows brightly with UV, so doesn’t make insects more visible;
2.      So doesn’t affect / increase predation;
OR
1.      Glows brightly with UV marking visible;
2.      So makes it easy to pick out labelled insects.
2
(d)     10 130.
Tolerance of ±1
 = 1 marks
2
(e)     1.      Scientists removed large numbers of insects (which were not returned) from same area / same population;
2.      Affecting ratio of marked to unmarked.
2
[10]
Q2.
(a)     1.      No interbreeding / gene pools are separate / geographic(al) isolation;
Accept: reproductive isolation as an alternative to no interbreeding.
2.      Mutation linked to (different) markings/colours;
3.      Selection/survival linked to (different) markings/colours;
4.      Adapted organisms breed / differential reproductive success;
Note: ’passed on to offspring’ on its own is not sufficient for reproduction.
5.       Change/increase in allele frequency/frequencies;
5
(b)     1.      (Compare DNA) base sequence / base pairing / (DNA) hybridisation;
Ignore: compare chromosomes / ‘genetic make-up’.
Accept: (compare) genes / introns / exons.
Note: reference to only comparing alleles is 1 max.
2.      Different in six (species) /different in different species / similar in three (subspecies) /similar in same species/subspecies;
Ignore: compare chromosomes / ‘genetic make-up’.
Reject: ‘same alleles/ same DNA bases in three species/subspecies’.
Note: mark point 2 can be awarded without mark point 1.
2
[7]
Q3.
(a)     Samples collected at random;
Method for choosing random sites – random
coordinates / position from tables / calculator / other suitable
means;
Other named factor constant e.g.:
Same size of net / same width of opening of net / use of one
quadrat / Quadrats of same size / of stated size / same area
disturbed / collect each 
Sample for same time;
3
(b)     Caenidae in deep water – because highest standard
deviation / ‘S.D.= 7.92’
1
(c)     (i)      An organism’s role / in the ecosystem / community;
[ALLOW refs. To trophic levels / named]
(IGNORE refs. To habitat)
1
(ii)     Caenidae found mainly in deep water AND Baetidae in
shallow water / one family mainly in deep water AND the
other in shallow water;
1
(iii)     Reduces competition for named factor – e.g. food / shelter / O_2 ;
To ensure both types survive / otherwise better adapted 
type displaces other type;
OR
Ref. to ‘Competitive exclusion principle’ = 2 marks
max 2
[8]
Q4.
(a)     (i)      Reliable / representative / for statistical tests;
Accept: identify anomalies
Neutral: accurate / valid / bias
1
(ii)     1.      Find coordinates (on a grid) / split area into squares / number the sites;
1. Ignore references to tape measures, metre rulers etc
2.      Method of generating / finding random numbers eg calculator / computer / random number generator / random numbers table;
2. Accept: numbers out of a hat / use of dice
2
(iii)    1.      Breeding (of lizards);
Neutral: weather / climate / hurricanes / hibernation / migration / emigration / immigration
2.      Food source / prey;
3.      Predator;
4.      Variation in malarial infection;
5.      Temperature variation;
6.      Availability of water eg drought / ߢrainy season’
2 max
(b)     1.      Number in sample varies;
2.      Allow a (valid) comparison;
2
(c)     1.      (Overall)  positive correlation  (for either / both species);
Neutral: only one study / no repeats
2.      Reference to (site) 5 / 300 metres;
3.      Limited results for A. wattsi / small sample / number / percentage infected for A. wattsi;.
2 max
(d)     (i)      1.      Fewer A.wattsi infected / more A. gingivinus infected;
2.      Higher number of A.wattsi present when higher percentage / number of A.gingivinus infected / no A.wattsi present when A.gingivinus has zero infection;
2
(ii)     1.      Reduced immunity / increased susceptibility to disease;
1. Accept: idea that energy / resources are used to combat malaria
2.      Reduced oxygen transport / uptake / respiration / reduced activity / movement;
2
(iii)    1.      There is a probability of less than 1% / 0.01;
1. Reject: probability is / equal to 1% / 0.01;
1. Reject 0.01% / 5% / 0.05 / 0.05%
2.      That result(s) / correlation / it is due to chance;
2. Allow correct interpretation using above (incorrect) figures eg there is a probability of less than 5% that the results are due to chance =1 mark
OR
3.      There is a probability of more than 99% / 0.99;
4.      That result(s) / correlation / it is not due to chance;
Note: there is a probability of more than 5% that the results are due to chance =0 marks
3. Reject: probability is / equal to 99% / 0.99;
3. Reject 0.99% / 95% / 0.95 / 0.95%
4. Allow correct interpretation of above figures ie 0.99% / 95% / 0.95 / 0.95% but reject if less than
2
[15]
Q5.
(a)     (i)      Will work in all weather conditions / hairs will stick to it even if shrew / animal is wet / withstand rain;
1
(ii)     So shrews come into contact with glue;
1
(b)     Avoids bias / allows statistical tests to be carried out;
Allow description
1
(c)     (i)      Increases the reliability of the measurements;
If measurements are repeatable, differences less likely to be due to measurement / personal error / anomalies unlikely;
Accept advantages of repeatable results. E.g. identifying anomalies / remove errors
2
(ii)     Plot graph / scatter diagram of one set of results against the other;
Q To gain first marking point, candidates must say what has been plotted.
Expect to see points lying close to line / Line should slope upwards / show positive correlation;
If what is being plotted is not clear, second point cannot be awarded.
OR
Plot measurement against hair number;
Look for overlying / corresponding points;
2
(d)     (i)      One mark for a valid explanation based on individual shrews entering more than one hair tube / many hairs from same shrew / shrews enter without leaving hair;
1
(ii)     Rules out differences due to changes in population / changes in environmental conditions;
That could be produced by births / deaths / migration / specific example of environmental conditions affects results;
2
(e)     (A statistical test) determines the probability of results being due to chance;
Enables null hypothesis / description of null hypothesis to be accepted / rejected / determines whether correlation / result is significant;
2
(f)      (i)      (Curve / line of best fit shows) positive correlation / description of positive correlation;
1
(ii)     Curve / line of best fit (almost) parallel to x-axis / horizontal / level / no correlation / index is independent of number of shrews;
Hair tubes with positive results when no shrews trapped;
Small size of shrews means shrews may not trigger traps;
2 max
[15]
Q6.
(a)     (i)      transect line may not go through representative areas / may avoid certain areas;
1
(ii)     large sample;
how random coordinates are generated / how random places
chosen;
2
(b)     (i)      spread of values around the mean height of the plant;
1
(ii)     smaller plants at higher altitude;
greater the altitude the lower the standard deviation ;
reference to figures to make a comparison;
2 max
(iii)     the plants measured were grown under uniform conditions;
1
[7]
Q7.
(a)     Greater when treated with herbicide G;
Same number but total biomass larger;
Can be shown by figures
2
(b)     Fewer weeds left to produce seeds;
Less contamination of crop (by weeds); / fewer weeds to separate from crop; / less competition (between crop and weeds);
2
(c)     Advantage
Weeds growing fast / photosynthesising fast so effect will be seen / 
will have large effect;
Disadvantage
No information about winter / other seasons / 
weeds not growing fast / 
could kill (beneficial) insects / 
crop may be harvested before effects noticeable;
One mark for advantage and
one mark for disadvantage
2
(d)     Limitations of investigation
1. No control / untreated field;
2. Amount of herbicide may be different;
3. May be differences between fields; Eg soil Nutrients / fertiliser added Type of weed Microclimates
4. May be different number of weeds (at start);
Limitations of results
5. No replicates / one set of data;
6. Field size may vary / not specified;
Scientific Research
7. Scientific research / example of scientific research has led to greater yield;
When marking please number the marking points
e.g.  means a mark award for point 5
5 max
[11]
Q8.
(a)     Tapes / string / axes laid out at right angles / grid area;
Method of obtaining random co-ordinates;
Do not allow “Use random number generator”
2
(b)     (i)      Decrease then remain constant;
From 200 cm / over 150 cm;
2
(ii)     Oxygen decreasing because soil becomes more compacted / not
replaced;
Decrease in oxygen leads to fewer aerobes surviving;
2
(c)     Anaerobic bacteria replace aerobic as oxygen decreased by aerobic bacteria;
Remove competition;
Aerobic bacteria no longer able to survive in these conditions;
3
(d)     (i)      Near the surface / in top 50 cm;
Table shows decrease with time at greater depths;
2
(ii)     Decrease;
Fewer aerobic bacteria with depth;
Oxygen concentration decreases / less oxygen at depth;
3
(e)     Probability greater than 95% / 0.95;
Results are not due to chance / results are significant;
Because bars do not overlap;
3
(f)      Plot as graph;
Draw line of best fit;
Read off appropriate value;
3
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