Author: Philip Colls
Document comments: Created by the \'abHTML to RTF .Net\'bb 5.8.2.9

Populations booklet revision questions           NAME:
Q1.
Scientists investigated the process of succession on sand dunes. They measured the percentage cover of different species of plants on sand dunes of different ages.
Some of the results the scientists obtained are shown in Figure 1.
Figure 1

(a)     Describe how you would determine the mean percentage cover for beach grass on a sand dune.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
(3)
(b)     The scientists concluded that the results shown in Figure 1 were due to succession taking place.
Use Figure 1 to explain why the scientists reached this conclusion.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
________________________________________________________________ (4)
The scientists also investigated how the proportion of sunlight reaching the ground changed during succession. Some of the results the scientists obtained are shown in Figure 2.
Figure 2

(c)     Use Figure 1 to explain the results in Figure 2.
___________________________________________________________________
_________________________________________________________________(1)
(d)     Using evidence from Figure 2, what can you conclude about the net primary productivity (NPP) in the sand dunes that are older than 1000 years?
Explain your answer.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
_______________________________________________(2)   (Total 10 marks)
Q2.  The photograph shows marram grass growing on a sand dune.
 
Marram grass on sand dune by Nigel Chadwick [CC-BY-SA], via Wikimedia Commons
(a)     Describe how you would investigate the distribution of marram grass from one
side of the dune to the other.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
 (3)
(b)     Marram grass is a pioneer species that grows on sand dunes. It has long roots
and a vertically growing stem that grows up through the sand.
Sand dunes are easily damaged by visitors and are blown by the wind. Planting
marram grass is useful in helping sand dune ecosystems to recover from damage.
Use your knowledge of succession to explain how.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
(2)
(Total 5 marks)
Q3.
A 75 m tall tree released very large numbers of small seeds. Ecologists used quadrats along a transect to measure the number of these seeds at different distances from the tree. Their results are shown on the graph.
 
The seeds of this tree are dispersed by wind. The diagram shows the pattern of seed dispersal from this tree.
 
(a)     Describe how the ecologists could have used quadrats and a transect to obtain the data from which the graph was drawn.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
(2)
(b)     Look at the diagram showing the pattern of seed dispersal from this tree.
(i)      Suggest an explanation for the shape of the line enclosing the area where the seeds landed.
______________________________________________________________
______________________________________________________________
______________________________________________________________
______________________________________________________________
(2)
(ii)     The line enclosing the area where the seeds landed would be different for trees of this species that were of a different height. Suggest why.
______________________________________________________________
______________________________________________________________
______________________________________________________________
______________________________________________________________
(2)
(c)     In an ecological succession, trees that are pioneer species often have smaller seeds than those that are part of a climax community.
(i)      The species of tree in this investigation is adapted to colonising areas that have been cleared of vegetation. Use information given above to explain how.
______________________________________________________________
______________________________________________________________
______________________________________________________________
______________________________________________________________
(2)

(ii)     The seeds produced by this species of tree did not grow successfully in a climax community. Suggest why.
______________________________________________________________
______________________________________________________________
______________________________________________________________
______________________________________________________________
_____________________________________________(2)  (Total 10 marks)
Q4. Dengue is a serious disease that is caused by a virus. The virus is carried from one person to another by a mosquito, Aedes aegypti. One method used to try to reduce transmission of this disease is the Sterile Insect Technique (SIT). This involves releasing large numbers of sterile (infertile) male A. aegypti into the habitat. These males have been made infertile by using radiation.
(a)     Explain how using the SIT could reduce transmission of dengue.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
_________________________________________________________________(2)
(b)     Describe how the mark-release-recapture method could be used to determine the population of A. aegypti at the start of the investigation.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
_________________________________________________________________(3)
(c)     The release of radiation-sterilised A. aegypti has not been very successful in controlling the transmission of dengue.
Suggest one reason why.
___________________________________________________________________
___________________________________________________________________
(1)
(d)     Recently a new method was developed to control A. aegypti. Scientists produced transgenic males carrying a ‘lethal gene’ which kills their offspring before they can reproduce.
The scientists released transgenic males every week in one area of a city in Brazil. At regular intervals they determined the number of A. aegypti per km^2 in the area where transgenic males were released and in a control area where no transgenic males were released.
The graph shows their results.
 
Suggest why the scientists released more transgenic males every week.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
(1)
(e)     The release of transgenic males proved successful in reducing the number of A. aegypti.
Describe how the results in the diagram above support this conclusion.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
(2)  (Total 9 marks)
Q5. A student investigated an area of moorland where succession was occurring. She used quadrats to measure the percentage cover of plant species, bare ground and surface water every 10 metres along a transect. She also recorded the depth of soil at each quadrat. Her results are shown in the table.
 
| Percentage cover in each quadrat A to E
| A | B | C | D | E
Bog moss | 55 | 40 | 10 | – | –
Bell heather | – | – | – | 15 | 10
Sundew | 10 | 5 | – | – | –
Ling | – | – | – | 15 | 20
Bilberry | – | – | – | 15 | 25
Heath grass | – | – | 30 | 10 | 5
Soft rush | – | 30 | 20 | 5 | 5
Sheep’s fescue | – | – | 25 | 35 | 30
Bare ground | 20 | 15 | 10 | 5 | 5
Surface water | 15 | 10 | 5 | – | –
Soil depth / cm | 3.2 | 4.7 | 8.2 | 11.5 | 14.8
– Indicates zero percentage cover.
(a)     Explain how these data suggest that succession has occurred from points A to E  along the transect.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
________________________________________________________________ (3)
(b)     The diversity of animal species is higher at E than A. Explain why.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
 (2)
(c)     The student used the mark-release-recapture technique to estimate the size of the population of sand lizards on an area of moorland. She collected 17 lizards and marked them before releasing them back into the same area. Later, she collected 20 lizards, 10 of which were marked.
(i)      Give two conditions for results from mark-release-recapture investigations to be valid.
1. ____________________________________________________________
2. __________________________________________________________ (2)
(ii)     Calculate the number of sand lizards on this area of moorland. Show your working.

Answer = ____________________(2)                (Total 9 marks)
Q6. Since 1965 there has been a steady rise in the phosphate concentration in the water of Lake Windermere. Scientists have monitored the phosphate concentration and plant biomass over a period of time. The results are shown in the graphs.
 
(a)     Suggest one source of the phosphate in the lake.
___________________________________________________________________
___________________________________________________________________
(1)
(b)     Calculate the percentage decrease in plant biomass between 1985 and 1995. Show your working.

Answer ____________________
(2)
(c)     From these graphs, a student concluded that changes in phosphate concentration caused changes in plant biomass. Explain why this conclusion may not be valid.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
(2)
(d)     Between 1982 and 1992 the number of fish in the lake decreased. Explain how the change in phosphate concentration may have resulted in this decrease in the fish population.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
(6)
(Total 11 marks)
Q7. To reduce the damage caused by insect pests, some farmers spray their fields of crop plants with pesticide. Many of these pesticides have been shown to cause environmental damage.
Bt plants have been genetically modified to produce a toxin that kills insect pests. The use of Bt crop plants has led to a reduction in the use of pesticides.
Scientists have found that some species of insect pest have become resistant to the toxin produced by the Bt crop plants.
The figure below shows information about the use of Bt crops and the number of species of insect pest resistant to the Bt toxin in one country.
 
      Year
(a)     Can you conclude that the insect pest resistant to Bt toxin found in the years 2002 to 2005 was the same insect species? Explain your answer.
___________________________________________________________________
_________________________________________________________________(1)
(b)     One farmer stated that the increase in the use of Bt crop plants had caused a mutation in one of the insect species and that this mutation had spread to other species of insect. Was he correct? Explain your answer.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
________________________________________________________________ (4)
(c)     There was a time lag between the introduction of Bt crops and the appearance of the first insect species that was resistant to the Bt toxin.
Explain why there was a time lag.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________(3) (Total 8 marks)
Q8. (a)     What term is used to describe populations of different species living in the same habitat?
_________________________________________________________________(1)
(b)     Different species occupy different ecological niches. Explain the advantage of species occupying different niches.
___________________________________________________________________
_________________________________________________________________(1)
Scientists recorded the number of water beetle species in 30 lakes. In each lake, they measured the pH of the water and recorded whether there were any fish present. The graph shows their results. 
 
(c)     A student concluded that a decrease in acidity caused an increase in the number of water beetle species. Evaluate this conclusion.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
_________________________________________________________________(3)
(d)     Explain how the presence of fish in a lake could cause an increase in the number of water beetle species.
___________________________________________________________________
_________________________________________________________________(1)
(Total 6 marks)
Q9. The organic material in household waste can be used to make compost for use as a fertiliser. Scientists investigated changes during one process used to make this compost. The method involved placing the waste in large containers for 150 days. At regular intervals the containers were rotated. The scientists measured the temperature of samples of waste during the investigation.
Figure 1 shows the results they obtained. The vertical bars show standard deviations.
Figure 1

(a)     Explain how microorganisms contributed to the increase in temperature during processing of organic waste.
___________________________________________________________________
___________________________________________________________________
_________________________________________________________________(2)
(b)     Explain the advantage of showing the data using standard deviations rather than ranges.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
_________________________________________________________________(2)
(c)     Suggest two advantages of rotating the containers during the process.
1. _________________________________________________________________
___________________________________________________________________
2. _________________________________________________________________
_________________________________________________________________(2)
(d)     The scientists took a sample of the waste at the start of the process. They then took samples every 30 days. In each sample, they determined the numbers of particular types of bacteria. Figure 2 shows the changes in the number of three types of bacteria during the process.
Figure 2
 
The scientists concluded that the results in Figure 1 and Figure 2 are evidence for a form of succession during the process.
Use the information to suggest how they reached this conclusion.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
(3)
(Total 9 marks)

Mark schemes
Q1.
(a)     1.      Method of randomly determining position (of quadrats) e.g. random numbers table/generator;
Ignore line/belt transect
2.      Large number/sample of quadrats;
Accept many/multiple
Ignore point quadrat
If a specified number is given, it must be 20 or more
3.      Divide total percentage by number of quadrats/samples/readings;
3
(b)     1.      Beach grass is the pioneer (species);
2.      Pioneers/named species change the (abiotic) environment/habitat/conditions/factors;
Must convey idea of change being caused by a species
Accept example of change e.g. more humus
3.      (So) less hostile for named species
OR
(So) more suitable for named species;
4.      Conifer/hardwood trees represent climax community;
4
(c)     Trees block/reduce (sun)light;
Reject ‘blocks’ all of the light
1
(d)     1.      (NPP) remains constant;
2.      GPP/photosynthesis and respiration constant;
Accept GPP/photosynthesis equals respiration
OR
3.      (NPP) low/decreases;
4.      Less light so less photosynthesis/GPP;
Reject no photosynthesis
Mark in paired statements
1 and 2 or 3 and 4
2
[10]
Q2.
(a)     1.      Transect / lay line / tape measure (from one side of the dune to the other);
1. & 2.   Reject random in context of placing transect / quadrats
2.      Place quadrats at regular intervals along the line;
Accept references to stratified sampling / different seral stages
3.      Count plants / percentage cover / abundance scale (in quadrats)
Accept abundance scale
OR
         Count plants and record where they touch line / transect;
3 max
(b)     1.      Stabilises sand / stops sand shifting;
2.      Forms / improves soil / makes conditions less hostile;
Allow credit for example of making conditions less hostile such as:
Adds nutrients
Improves water retention
2
[5]
Q3.
(a)     1.      Quadrats placed at intervals along transect;
2.      Number of seeds counted per quadrat to calculate seeds per m^2;
2
(b)     (i)      1.      Wind from North East;
Accept blowing to South West
2.      Seeds blown further;
2
(ii)     1.      Seeds have different distances to fall / seeds have different times in air;
2.      Blown by wind a different amount;
3.      (Candidates investigation) shows that seeds travel further when dropped from higher;
Supported by reference to candidate’s investigation
2 max
(c)     (i)      1.      Produces large number of seeds / produces seeds blown by wind;
2.      Greater probability (of colonising);
Accept greater chance
2
(ii)     1.      Small size;
2.      Too little food in seed to become established;
3.      Not enough light for photosynthesis;
2 max
[10]
Q4.
(a)     1.      Compete (with fertile males) to mate / for food / resources
OR
intraspecific competition;
2.      Do not reproduce / breed
OR
Reduces population (of mosquitoes);
1.      Must convey idea of competition.
2.      Accept: ‘fewer mosquitoes’ / ‘fewer offspring’.
2
(b)     1.      Capture / collect / sample, mark and release;
2.      Leave time for mosquitoes / Aedes to disperse before second sampling / collection;
3.      (Population =) number in first sample × number in second sample divided by number of marked in second sample / number recaptured;
3.      Accept: correct equation.
3
(c)     (Radiation) affects their ‘attractiveness’ / courtship / survival / life span;
Accept: ‘die / less likely to survive due to radiation’.
Accept: ‘disease can be transmitted by other means’ (other than mosquitoes).
1
(d)     To maintain number / competition as they die / have a short life span;
Accept: to replace mosquitoes that have died.
1
(e)     1.      Number (of mosquitoes in treated area) is low / lower at / after 12/13/14/15/16 weeks = 2 marks;
2.      For one mark accept number (of mosquitoes in treated area) is low/lower without reference to relevant week;
Accept: amount for number.
Accept: comparison of numbers (of mosquitoes) for lower/low.
2
[9]
Q5.
(a)     1.      Decrease in (percentage cover) of bare ground / water linked to more plants / species / increase in plant coverage;
Allow one maximum mark for answers which describe all three changes without a suitable explanation for any change
Must be idea of more / increase not just change in species / plants
2.      Change in diversity / number of plant / species / named (species) as abiotic conditions altered / due to competition / more soil / less hostile;
Accept pioneer species replaced due to competition
Accept description of change in species
Accept ‘more suitable’ = less hostile
3.      Increase in depth of soil as plants die / humus formed;
3
(b)     1.      Greater variety of food / more food sources;
‘More food’ = neutral
2.      More / variety of habitats / niches;
Ignore ‘more homes’ or reference to ‘shelters’ 
2
(c)     (i)      1.      Marking is not removed / marking does not affect survival / predation;
2.      Limited / no immigration / emigration;
Accept ‘migration’ and descriptions of immigration / emigration
2. and 4. Increase / decrease in population is not sufficient – there must be a reason
3.      Sufficient time for (marked) individuals to mix (within the population);
Accept – ‘For mixing to occur between samples’ 
4.      No / little births / deaths / breeding;
5.      Sampling method is the same;
Ignore ‘random sampling’ 
2 max
(ii)     Correct answer of ...34 = 2 marks;
Allow one mark for an answer of 51 as candidate has misinterpreted the second sample as being = 30
Incorrect answer but shows correct formula in words or numbers
e.g. 17 × 20 ÷ 10;
Reject correct formula multiplied by 100
2
[9]
Q6.
(a)     Fertilisers / detergents / slurry / manure / sewage / faeces;
1
(b)     (31 – 5) / 31 x 100% / single error in otherwise correct method;
83.87 / 83.9 / 84%;
2
(c)     Have continuous data for phosphate but not for biomass;
Effect of named factor explained;
2
(d)     1.      Increased phosphate causes increase in plant growth / algal bloom;
2.      Plants (cover surface and) block out light so plants (under surface) die;
3.      Increase in (aerobic) bacteria / decomposers (which break down plants);
4.      Bacteria / decomposers use up oxygen / reduce oxygen conc. in water;
5.      In respiration;
6.      Plants unable to photosynthesise so less oxygen produced;
max 6
[11]
Q7.
(a)     (No – no mark)
Graph / bar chart only shows number of species, not the name of the species.
1
(b)     (No – no mark)
1.      Mutations are spontaneous / random;
2.      Only the rate of mutation is affected by environment;
3.      Different species do not interbreed / do not produce fertile offspring;
4.      So mutation / gene / allele cannot be passed from one species to another.
Ignore references to correlation does not prove causation
4
(c)     1.      Initially one / few insects with favourable mutation / allele;
2.      Individuals with (favourable) mutation / allele will have more offspring;
3.      Takes many generations for (favourable) mutation / allele to become the most common allele (of this gene).
3
[8]
Q8.
(a)     Community;
1
(b)     (Less) competition for food/resource;
Ignore: competition for niche/habitat.
Accept: space/named resource.
Reject: intraspecific competition.
1
(c)     1.      Correlation but does not mean a causal effect;
Ignore: positive/ negative (correlation).
2.      Other abiotic/biotic/named factor involved;
Accept: due to presence/absence of fish.
Reject: ‘other factors’ unless further qualified.
3.      Variation in numbers of beetles species at same/similar particular pH;
Accept: same number of beetles at different pHs.
Accept: ‘scattered results’ / ‘anomalies’ / ‘spread of results’.
4.       Large sample;
Max 3
(d)    Fish feed on predator/consumer of water beetle;
Accept: beetles feed on fish/faeces.
1
[6]
Q9.
(a)     1.      Respiration/metabolism/ammonification;
2.      (Releases/produces) heat;
Reject: ‘produces energy’.
2
(b)     1.      SD is spread of data around the mean;
Accept: variation around the mean.
Accept: range is difference between highest and lowest values/extremes or range includes anomalies/outliers.
2.      (SD) reduces effect of anomalies/ outliers;
Reject: (SD) removes anomalies/outliers.
3.      (SD) can be used to determine if (difference in results is) significant/not significant/due to chance /not due to chance;
Ignore: reliability/accuracy/validity.
2 max
(c)     1.       Distributes heat / prevents ‘hot’ spots;
2.      Distributes microorganisms;
3.      More enzyme-substrate complexes;
4.      Increases rate of decomposition;
Accept: increases nitrification/ammonification or ‘breaks down waste faster’.
5.       Aeration/provides oxygen;
2 max
(d)     1.      Microorganisms change the abiotic conditions/temperature/organic waste /provide nutrients;
Must refer to microorganisms or bacteria/named bacteria causing the change.
Ignore: change the environment.
2.      Less hostile conditions;
3.      Decline in Cocci and increase in rods;
Accept: ‘decrease in cocci, others are going up’.
Accept: decrease in cocci and increase in either rod type or increase in both types.
4.      Gram positive outcompete / better competitors;
Accept: rods outcompete (cocci) / better competitors.
3 max
[9]