IB DP Biology Topic 4: Ecology : 4.1 Species, communities and ecosystems Question Bank HL Paper 2


Dolly the sheep was the first mammal to be cloned from an adult somatic cell.

Which DNA did Dolly inherit?
A. Nuclear and mitochondrial DNA from the surrogate ewe
B. Nuclear and mitochondrial DNA from the Finn-Dorset
C. Mitochondrial DNA from the Scottish Blackface and nuclear DNA from the Finn-Dorset
D. Mitochondrial DNA from the Scottish Blackface and nuclear DNA from the surrogate ewe


Markscheme : C


Remote sensing satellites are used to monitor the Earth’s ecosystems. One measure of ecosystem status is leaf area index (LAI), which is the total area of leaves in square metres per square metre (\(m^2\) \(m^{-2}\)) of the Earth’s surface. The graph shows LAI estimates, calculated
using data from the Global Inventory Monitoring and Modelling System (GIMMS), during the period from 1981 to 2011. The data points are monthly averages in four latitudinal zones in the northern hemisphere

(a) Compare and contrast the LAI data for the arctic and temperate zones.

(b) Suggest reasons for the differences in LAI between the boreal and equatorial zones.

There is evidence of a change in mean LAI values on Earth over recent decades. Changes can be quantified by calculating LAI anomalies. These are differences between annual LAI values and the mean LAI for the entire given time period. The graph shows global LAI anomalies for the period from 1981 to 2014, based on data from GIMMS. It also shows mean global LAI anomalies between 1981 and 2009, based on data from three other remote sensing programmes. Vertical bars show the timing of El Niño events. The darkness of the bars indicates the intensity of the El Niño events. The darker the bar, the more intense the event.

(c) Analyse the data shown in the graph for evidence of a relationship between LAI and El Niño events.

(d) The data in the graph show a long-term trend in global LAI.
(i) State the trend.
(ii) Global ecosystem modelling suggests that most of the change in LAI is due to increases in atmospheric carbon dioxide. Explain how rising atmospheric carbon dioxide (\(CO_2\)) concentration could cause the observed change in LAI.

The 2015 Paris Agreement sets out an international framework for avoiding dangerous climate change. A key aspect is conserving and enhancing sinks of greenhouse gases, including forests. Free air carbon dioxide enrichment (FACE) experiments are being used to investigate whether increases in atmospheric \(CO_2\) concentration will cause biomass increases in existing forests. Three FACE experiments have been running for at least ten years in young, developing forests. Photosynthesis rates are measured in 25 to 30 m diameter plots. In control plots, carbon dioxide concentrations remain at current atmospheric levels (ambient \(CO_2\)). In treatment plots, the \(CO_2\) concentration is raised by 50% (elevated \(CO_2\)). The table gives some details of these experiments and the highest annual net primary production recorded during the period of the experiment. Net primary production is the mass of carbon absorbed and fixed by photosynthesis in plants that is not released due to plant respiration.

(e) State the effect of elevated \(CO_2\) on net primary production in these young, developing forests.

(f) Outline one benefit of conducting similar FACE experiments in multiple locations.

In each forest, there are two or three trial plots per \(CO_2\) treatment. The bar chart shows the allocation of carbon from net primary production to different parts of the trees in these trial plots.

(g) Evaluate the evidence from the bar chart that increases in carbon dioxide cause increases in carbon storage in young, developing forests.


Answer :

(a) Similarity
both rise to peak/maximum/are highest in summer/warmest
both lowest in winter/December/January
both rise then fall;
temperate always higher/higher overall/higher throughout year
temperate peak is higher/is one month later/is in August versus July in arctic;

a. climate/temperature/light consistent throughout year in equatorial but seasonal variation in boreal;
b. conditions suitable for photosynthesis throughout the year in equatorial but not in boreal;
c. temperatures higher/growing season longer in equatorial versus lower/shorter in boreal;
d. water frozen/unavailable in boreal during winter whereas always available in equatorial;
e. shorter daylengths in winter in boreal (than those months in equatorial so lower LAI);
f. boreal LAI higher (than equatorial) in July due to longer daylengths;
g. equatorial trees/plants are evergreen / boreal trees/plants are deciduous/have less/no leaves in winter;
h. variation in angle of light rays (between different latitudes);

a. decreases in LAI during El Niño
increases in LAI between El Niño events;
b. 1983-4/other example of a decrease during El Niño
1984-6/other example of increase between El Niño events;
94-95/2009 anomalous as LAI rises during El Niño event;
99-2000 anomalous as LAI decreases between El Niño events;
c. larger decrease (in LAI) with more intense/longer El Niño events
no/less decrease during less intense/briefer El Niño events;

i. Increase/increasing/upwards/rising (trend);
ii. a. more photosynthesis (with higher carbon dioxide concentration);
    b. more plant growth/more (plant) biomass/more leaves/more plants;

increases it/higher (maximum annual net primary production);

check whether trend is confirmed/replicated/not specific to some forests
investigate worldwide effects (of rising carbon dioxide)
(check whether results are affected by) differences in tree species/types of
tree/soil types/rainfall/temperature/climate/latitudes/conditions/biome/ecosystem;

a. more carbon stored/allocated (by the tree as a whole) with elevated carbon dioxide;
b. evidence (from the bar chart) is strong (for the trend/hypothesis);
c. all elevated plots have more carbon stored than all ambient plots in all sites/no
d. more/most carbon allocated to wood (in stems and roots) with elevated carbon
e. more carbon allocated to narrow roots/leaves with elevated carbon dioxide;
f. narrow roots increase most in Oak Ridge;
g. most increase in wood (in stems and roots) in Rhinelander and Duke;
h. much/more variation between plots at Oak Ridge (than at Rhinelander and
i. no error bars so significance of differences is uncertain;


  1. (a) Outline the roles of helicase and ligase in DNA replication. [4]
  2. (b) Explain how natural selection can lead to speciation. [7]
  3. (c) Outline the features of ecosystems that make them sustainable




a. unwinds/uncoils the DNA «double helix» ✔
b. breaks hydrogen bonds «between bases» ✔
c. separates the «two» strands/unzips the DNA/creates replication fork ✔ ligase:
d. seals nicks/forms a continuous «sugar-phosphate» backbone/strand ✔
e. makes sugar-phosphate bonds/covalent bonds between adjacent nucleotides ✔
f. after «RNA» primers are removed/where an «RNA» primer was replaced by DNA ✔
g. «helps to» join Okazaki fragments ✔


a. variation is required for natural selection/evolution/variation in species/populations ✔
b. mutation/meiosis/sexual reproduction is a source of variation ✔
c. competition/more offspring than the environment can support ✔
d. adaptations make individuals suited to their environment/way of life ✔
e. survival of better adapted «individuals)/survival of fittest/converse ✔
f. inheritance of traits/passing on genes of better adapted «individuals»
reproduction/more reproduction of better adapted/fittest «individuals» ✔
g. speciation is formation of a new species/splitting of a species/one population becoming a separate species ✔
h. reproductive isolation of separated populations ✔
i. geographic isolation «of populations can lead to speciation» ✔
j. temporal/behavioral isolation «of populations can lead to speciation» ✔
k. disruptive selection/differences in selection «between populations can lead to speciation» ✔
l. gradual divergence of populations due to natural selection/due to differences in environment ✔
m. changes in the gene pools «of separated populations»/separation of gene pools ✔
n. interbreeding becomes impossible/no fertile offspring «so speciation has happened» ✔


a. recycling of nutrients/elements/components/materials ✔
b. carbon/nitrogen/another example of recycled nutrient/element ✔
c. decomposers/saprotrophs break down organic matter/release «inorganic» nutrients ✔
d. energy supplied by the sun
energy cannot be recycled «so ongoing supply is needed»
energy is lost from ecosystems as heat ✔

energy flow along food chains/through food web/through trophic levels ✔ photosynthesis/autotrophs make foods/trap energy
autotrophs supply the food that supports primary consumers ✔

g. oxygen «for aerobic respiration» released by autotrophs/photosynthesis/plants ✔
h. carbon dioxide «for photosynthesis» released by respiration ✔
i. populations limited by food supply/predator-prey/interactions/competition
populations regulated by negative feedback
fewer/less of each successive trophic level «along the food chain»/OWTTE ✔
j. supplies of water from rainfall/precipitation/rivers/water cycle ✔


(a) Distinguish between the transfers of energy and inorganic nutrients in ecosystems. [2]

(b) Outline the role of methanogenic archaeans in the movement of carbon in ecosystems. [2]

(c) Describe how autotrophs absorb light energy.   [3]



a energy is lost (between trophic levels) / not all passed on / not reused / must be supplied; nutrients are recycled/reused;


a methane produced from organic matter;

b in anaerobic conditions;

c methane diffuses into atmosphere/accumulates in ground/soil;

d oxidized/converted to carbon dioxide (in atmosphere);


a light absorbed by (photosynthetic) pigments;

b chlorophyll absorbs blue and red / drawing of absorption spectrum for chlorophyll;

c photosystems are groups of pigment molecules/are light harvesting complexes;

d photosystems are located in thylakoid membranes; e electrons excited/raised to higher energy level;


The image shows a food web.

Using the food web, identify a detritivore.


Using the food web, identify a saprotroph.


State the name of the domain to which birds, such as the Elf owl, belong.


Outline the energy flow through this food web.






Do not accept protozoans or nematodes as they are consumers.




a. light energy of Sun is converted by plant/autotroph to chemical energy «in carbon compounds through photosynthesis» 

b. detritivores/saprotrophs decay plant material «that accumulates in the soil» to obtain energy  OWTTE

c. consumers release energy from the carbon compounds by cell respiration energy lost as heat 

d. energy is used by organisms for metabolism 

e. energy is transferred between organisms/trophic levels through the food chains/web  
For mp e, accept specific example such as energy is transferred from primary to secondary consumer etc.

f. energy is lost at each trophic level «so lengths of food chains/web are restricted»
approximately 80/90 % of energy is lost «between trophic levels»
Vice versa

Award mark points that refer to the specific organisms from this food web.



Common shrews (Sorex araneus) are small mammals found in Northern Europe. Their diet includes insects, slugs, spiders, worms and amphibians. They do not hibernate in winter because their bodies are too small to store sufficient fat reserves.

To study brain size in shrews, researchers anesthetize them, X-ray their skulls and measure the height of the braincase (BCH) where the brain is located. The graph shows the relationship between BCH and the brain mass of individual adult shrews.

(a) State the relationship between BCH and brain mass of shrews. [1]

(b) Outline how the shrew labelled P differs from the normal relationship between BCH and brain mass. [1]

(c) Suggest a reason that researchers use BCH rather than brain mass to indicate brain size. [1]

The researchers found that the BCH of any individual adult shrew could vary seasonally. They collected shrews at different times of the year. The BCH of each shrew was compared with its body mass. The results are displayed in the chart.

(d) State the season when shrew brain mass is greatest.[1]

(e) Compare and contrast the results for winter and spring.[2]

(f) Suggest a reason for the difference in BCH in summer and winter. [1]

Shrews were observed in different seasons and the time they spent on a particular activity was recorded and expressed as a percentage of the total observation time. The circles in the kite shapes represent the mean value of time for each activity.

(g) State the activity and season that occupied the greatest mean percentage of observation time. [1]

(h) Suggest a reason for the difference in the time observed eating and drinking. [2]

The researchers were interested in the seasonal differences in searching for food. They set up a square arena with sides of 110cm and four entrances (A, B, C and D). Containers were placed in the arena, some with food and others with no food. The diagram shows a top-down view of the arena.

Each shrew was starved of food for two hours before its cage was opened at one of the entrances to the arena. The length of the path taken by the shrew to obtain food was measured. This was standardized by dividing the path length by the straight-line distance from the entrance to the containers with food. Each shrew was used for 10 trials.

The graph shows the standardized mean path length taken by all the shrews at different seasons of the year. The letters show where the cages were placed for each trial.

(i) Calculate the percentage of containers that contained food. [1]

(j) Outline a reason that the path length was standardized. [1]

(k) Compare and contrast the results for trials 2 and 9.[2]

(l) With reference to all the data, suggest a reason for the difference in standardized mean path length for summer and winter. [2]


a positive correlation/the greater the BCH the greater the brain mass;

b a. high BCH but brain mass is low/lower than expected/lower than others with similar BCH;

b. (fairly) low brain mass but BCH is high/higher than expected/higher than others with similar brain mass;

c easier to measure/doesn’t require dissection/non-invasive / shrew not harmed/killed/more ethical;

d Summer;

e Compare part of answer = similarity:

a. both have low BCH (compared with summer); Contrast part of answer:
b. greater body mass in spring than winter;
overall/mean/average BCH higher in spring than in winter;
more variation in body mass in spring than winter;

f a. large brain (indicated by large BCH) requires/uses much energy;
b. shrews need/use much energy in winter (other than for the brain);
c. much energy used in winter for keeping warm/searching for food;
d. food/energy more abundant in summer/less abundant in winter;
e. growth between winter and summer (so BCH larger in summer);

g resting in spring; 
h a. more food/energy eaten/required in winter/cold;

b. food needed to maintain temperature/stay warm/generate heat;
c. more loss of body heat in cold conditions;
d. more energy used hunting for food;
e. food less available in winter/harder to find enough food;

i 4(%);

j compensates for the different distances between entrances and food/OWTTE;

to enable (fair/valid) comparison/OWTTE;

k Similarity between 2 and 9:

a. winter path length longer (than spring and summer) in both (trials 2 and 9/from
entrances B and C);
Contrast between 2 and 9:
b. path length longer in trial 2 than 9/from entrance B than entrance C (in all  seasons);
error/bar/standard deviation/variation in data greater in trial 2 than 9/from entrance B than entrance C (in all seasons);

l a. in winter shrews have smaller brains/smaller BCH / converse for summer;

b. lower/poorer memory/thinking/cognitive skills/learning/intelligence/senses/sense of smell/ability to find food in winter/ converse for summer;

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