D4.
2 Past paper practice [123 marks]
1. [Maximum mark: 6] 24M.2.HL.TZ1.119
Discuss how wild fish populations are assessed to ensure sustainable
fishing practices. [6]
2. [Maximum mark: 6] 24M.2.HL.TZ2.119
Discuss the risks and benefits associated with the use of phosphate
fertilizers in agriculture. [6]
3. [Maximum mark: 11] 19N.2.SL.TZ0.5
(a) Outline the principles used by scientists to classify organisms. [4]
(b) Explain the movement of energy and inorganic nutrients in an
ecosystem. [7]
4. [Maximum mark: 1] 24N.1A.SL.TZ1.18
A simple sealed terrestrial mesocosm was set up to demonstrate that
natural ecosystems can be sustainable over long periods of time.
What indicates that the mesocosm is still sustainable after several
months?
A. Wastes are constantly recycled.
B. The diversity of living organisms increases.
C. Energy is conserved.
D. The mass of carbon increases.
[1]
5. [Maximum mark: 1] 23N.1A.HL.TZ1.11
Which factor(s) would be expected to vary in a closed terrestrial
mesocosm?
I. Carbon content
II. Temperature
III. Biomass
A. I only
B. I and II only
C. II and III only
D. I, II and III [1]
6. [Maximum mark: 1] 21N.1A.SL.TZ0.17
What is exchanged between a sealed mesocosm and the surrounding
external environment?
A. Energy
B. Water
C. Air
D. Nothing can pass [1]
7. [Maximum mark: 1] 19M.1A.SL.TZ2.19
Which is not essential in a viable mesocosm?
A. Light source
B. Autotroph
C. Saprotroph
D. Herbivore
[1]
8. [Maximum mark: 8] SPM.2.HL.TZ0.9
Various mechanisms can lead to inhibition in biological systems. A toxin is a
substance capable of disrupting metabolic processes in organisms.
(a) Describe how toxins such as DDT might concentrate in the
bodies of birds. [4]
(b) Rotenone is a naturally occurring toxin that blocks the electron
transport chain in insects and fish. Outline the consequences of
exposure to a toxin like rotenone for cell respiration. [4]
9. [Maximum mark: 6] 24N.2.SL.TZ1.113
Mount Saint Helens, located in the Pacific Northwest of the United States,
erupted in 1980. This 2007 photograph shows the growth of vegetation on the
base and sides of the volcano.
[Source: Curved Light USA / Alamy Stock Photo, 2009. Regrowth in the blast plain in front of Mount St Helens volcano.
[image online] Available at: https://www.alamy.com/stock-photo-regrowth-in-the-blast-plain-in-front-
of-mount-sthelens- volcano-37924867.html [Accessed 3 April 2019]. Source adapted.]
(a) Outline the process of primary succession following the
eruption of a volcano like Mount Saint Helens. [3]
(b) In communities next to Mount Saint Helens, there is a
relationship between the red squirrel (Tamiasciurus hudsonicus) and
the Sitka spruce tree (Picea sitchensis). The main food source of the
squirrel is the seeds found in the cones produced by the spruce
trees. The squirrel buries the cones but does not always find
them again to eat the seeds.
(b.i) Describe how the squirrel and the spruce tree benefit from the
interactions between them. [2]
(b.ii) Identify the trophic level of the squirrel in this food chain. [1]
10. [Maximum mark: 5] 24N.2.SL.TZ2.116
The sinking of the tanker Eurobulker off the coast of Greece in September 2000
resulted in a spill of 700 tonnes of crude oil. The sands in the oil spill region were
categorized according to the level of pollution and the presence of indicator
species.
The graph shows the trends in richness of all species in the five ecological quality
status categories in sands after the oil spill.
[Source: Simboura, N. and Zenetos, A., 2002. Mediterranean Marine Science 3(2), pp. 77–111. Reference redacted.
Source adapted.]
(a) Analyse the data to show that pollution affects biodiversity. [2]
(b) Outline how the biomagnification of chemicals from crude oil
could occur in marine food chains. [3]
11. [Maximum mark: 5] 24M.2.HL.TZ1.103
Growth rates of marine algae can be investigated using experimental
mesocosms such as those shown.
[Source: Mosley, L., Reid, R., 2015. Figure 9. [image online] Available at:
https://www.researchgate.net/figure/Variation-in-mesocosmplant-composition-and-probes-for-
continuous-monitoring-of-pH-Eh_fig5_328661328.
University of Hawaiʻi at Mānoa, 2003. Grac parvis herb2. [image online]. Available at:
http://www.hawaii.edu/reefalgae/invasive_algae/rhodo/grac%20parvis%20herb%202.jpg [Accessed 22
August 2019].
Novák, J., n.d. Ulva lactuca L. – Sea Lettuce. [image online] Available at: https://www.biolib.cz/en/image/id7080/
[Accessed 22 August 2019].]
Data are shown for percentage growth rates of red algae, grown in their natural
environment and using mesocosms. The conditions investigated included
competition from green algae and from elevated CO2, as well as competition
from green algae combined with elevated CO2.
[Source: Young, C.S. and Gobler, C.J., 2017. The organizing effects of elevated CO2 on competition among
estuarine primary producers. Nature, [online] Available at: https://www.nature.com/articles/s41598-017-
08178-5 [Accessed 22 August 2019]. Source adapted.]
(a) Outline the effect of elevated CO2 on the percentage growth
rate of the red algae. [2]
(b) Suggest a possible reason for the elevated percentage growth
rates of red algae in the mesocosms compared with the
percentage growth rate in their natural environment. [1]
(c) Describe how the photosynthetic pigments in the algae can be
identified. [2]
12. [Maximum mark: 10] 24M.2.HL.TZ1.116
Aedes japonicus and Aedes albopictus are invasive mosquito species that have recently
become established in Western Europe. A. japonicus is more suited to the cooler
regions in central Europe, while A. albopictus is adapted to warmer temperatures of
the Mediterranean regions.
[Source: CDC/Frank Collins, PhD. https://phil.cdc.gov/details.aspx?pid=7887. Public domain.
CDC/James D. Gathany. https://phil.cdc.gov/details.aspx?pid=4487. Public domain.]
(a) Outline two other ways, apart from preferred climate, in which
the niches of these species may differ. [2]
(b) Suggest a possible impact of increasing mean temperatures in
Europe on the distribution of A. albopictus. [1]
(c) Predict possible outcomes for the two species in regions of
Europe where the niches overlap. [2]
(d) Discuss the benefits and risks of using DDT to control
mosquitoes. [3]
(e) Outline the environmental concerns surrounding marine
macroplastic pollution. [2]
13. [Maximum mark: 8] 24M.2.HL.TZ2.5
In fruit flies (Drosophila melanogaster), the allele for brown body (B) is dominant to
black body (b) and the allele for long wings (L) is dominant to short wings (l). A
dihybrid cross was made between a fruit fly heterozygous for both traits and a
black, short-winged fruit fly, as shown in the image.
The expected and observed ratios of offspring of the cross are given.
(a) Explain the differences between the expected and observed
phenotypic ratios of the cross. [3]
(b) Fruit flies are sometimes kept in enclosed glass mesocosms to
study their population dynamics, genetics and interactions with
the abiotic environment.
Explain the advantages of using mesocosms in these studies. [2]
(c) Outline the experiment carried out by Hershey and Chase that
provided evidence that DNA is the genetic material in
organisms. [3]
14. [Maximum mark: 5] 24M.2.HL.TZ2.118
An investigation was undertaken in Gåsbreen, Norway, in a freshly de-glaciated
area to look at the organisms present at different times since the retreating
glacier had exposed the land. A linear transect and 1 m2 quadrat were used
starting at the edge of the retreating glacier. The first producers were recorded at
a distance of 426 m from the glacier.
[Source: Wietrzyk, P., et al., 2016. Fig. 2. Stages of succession on the Gåsbreen foreland. [graph] (Polish
Polar Research, 37(4), p. 499).]
(a) Outline how a transect and quadrats can be used in ecological
fieldwork. [2]
(b) Identify which group of organisms had the highest percentage
coverage of the area studied. [1]
(c) Outline the type of succession shown here. [2]
15. [Maximum mark: 6] 24M.2.SL.TZ1.103
Growth rates of marine algae can be investigated using experimental
mesocosms such as those shown.
[Source: Mosley, L., Reid, R., 2015. Figure 9. [image online] Available at:
https://www.researchgate.net/figure/Variation-inmesocosmplant-composition-and-probes-for-
continuous-monitoring-of-pH-Eh_fig5_328661328.
University of Hawaiʻi at Mānoa, 2003. Grac parvis herb2. [image online]. Available at:
http://www.hawaii.edu/reefalgae/invasive_algae/rhodo/grac%20parvis%20herb%202.jpg [Accessed 22
August 2019].
Novák, J., n.d. Ulva lactuca L. – Sea Lettuce. [image online] Available at: https://www.biolib.cz/en/image/id7080/
[Accessed 22 August 2019].]
Data are shown for percentage growth rates of red algae, grown in their natural
environment and using mesocosms. The conditions investigated included
competition from green algae and from elevated CO2, as well as competition
from green algae combined with elevated CO2.
[Source: Young, C.S. and Gobler, C.J., 2017. The organizing effects of elevated CO2 on competition among
estuarine primary producers. Nature, [online] Available at: https://www.nature.com/articles/s41598-017-
08178-5 [Accessed 22 August 2019]. Source adapted.]
(a) Outline the effect of elevated CO2 on the percentage growth
rate of the red algae. [2]
(b) State one advantage of conducting research using mesocosms. [1]
(c) Explain how to set up a mesocosm in a sealed container. [3]
16. [Maximum mark: 5] 24M.2.SL.TZ2.113
(a) The red lionfish (Pterois volitans) is an aggressive predator that
inhabits coral reefs. It is native to the Indo-Pacific ocean but has
recently been found in Florida, the Gulf of Mexico and the
Caribbean and is considered to be an invasive species.
[Source: Pterois volitans, NMNZ P.039101. [image online] Available at:
http://fishesofaustralia.net.au/Images/Image/PteroisVolitansNORFANZ.jpg. Photo
by NORFANZ Founding Parties, 2003.]
[3]
Discuss the impact that the presence of this fish could have in
the Gulf of Mexico.
(b) Outline the effect of DDT on the environment. [2]
17. [Maximum mark: 7] 23N.2.HL.TZ2.116
Feeding relationships between organisms on rocky shores along the Pacific
Coast of North America were studied. The food web shows the proportions of the
total energy consumed by the two carnivorous species, a starfish (Pisaster ochraceus)
and a small gastropod (Thais emarginata).
[Source: Food web: Used with permission of University of Chicago Press -
Journals, from The American Naturalist, Essex Institute, American Society of Naturalists,
Vol 100, No 910, 1966; permission conveyed through Copyright Clearance Center,
Inc.
Pisaster image: jkirkhart35, CC BY 2.0 https://creativecommons.org/licenses/by/2.0,
via Wikimedia Commons.]
Thais image: H. Zell, CC BY-SA 3.0 https://creativecommons.org/licenses/by-sa/3.0,
via Wikimedia Commons.]
Chitons image: Ryan Wick. https://flic.kr/p/5CRYNs. Licensed under CC BY 2.0
https://creativecommons.org/licenses/by/2.0/.
Limpets image: EllaGervaise. https://flic.kr/p/5MQENM. Licensed under CC BY 2.0
https://creativecommons.org/licenses/by/2.0/. Image adapted.
Bivalves image: Oxford University Museum of Natural History.
Acorn barnacles image: Kandukuru Nagarjun. https://flic.kr/p/Q9FUGa. Licensed
under CC BY 2.0 https://creativecommons.org/licenses/by/2.0/.
Mytilus image: Dentren at English Wikipedia, CC BY-SA 3.0
https://creativecommons.org/licenses/by-sa/3.0, via Wikimedia Commons.]
(a) Identify the main source of energy of Thais. [1]
(b) Limpets feed on photosynthetic algae. Identify the trophic level
of limpets. [1]
(c) Predict what would happen to this community if the following
organisms were removed from the ecosystem.
(c.i) Mytilus: [1]
(c.ii) Acorn barnacles: [2]
(c) Pisaster is considered a keystone species. Explain the effects of
Pisaster on this community. [2]
18. [Maximum mark: 7] 23N.2.HL.TZ2.117
Stonefly nymphs (Plecoptera) are good indicators of unpolluted streams and rivers.
Graph I shows the effect of a sewage outfall on oxygen concentration and
biochemical oxygen demand (BOD) in a stream. Graph II shows the distribution
curves of three different aquatic species living in the stream.
[Source: Hynes, H.B.N., 1960. The Biology of Polluted Waters. Liverpool: Liverpool
University Press.]
(a) Identify which curve in graph II shows the distribution of
stonefly nymphs. [1]
(b) Outline the use of indicator species such as stoneflies to assess
the quality of aquatic environments. [3]
(a) Explain the effect of eutrophication on BOD. [3]
19. [Maximum mark: 5] 23M.1B.SL.TZ2.3
Laboratory-scale mesocosms were built to investigate the effect of very small
contaminants (nanoparticles) on ramshorn snails (Planorbarius corneus).
[Source: Material from: Auffan, M., Tella, M., Santaella, C., Brousset, L., Pailles, C., Barakat, M., Espinasse, B.,
Artells, E., Issartel,
J., Masion, A., Rose, J., Wiesner, M.R., Achouak, W., Thiery, A. and Bottero, J.-Y., An adaptable mesocosm
platform
for performing integrated assessments of nanomaterial risk in complex environmental systems,
published 2014, Nature
Scientific Reports, reproduced with permission of SNCSC.]
(a) State two variables measured by the probes.
1:
[2]
2:
(b) Suggest one advantage of using a mesocosm in this type of
research. [1]
(c) Outline the requirements for sustainability within a sealed
mesocosm. [2]
20. [Maximum mark: 2] 19N.2.SL.TZ0.b
Models are used as representations of the real world. Evaluate the use
of food webs to represent ecological communities. [2]
21. [Maximum mark: 2] 19N.2.SL.TZ0.c
Describe the major characteristics of a eutrophic lake. [2]
22. [Maximum mark: 3] 19N.2.SL.TZ0.13
(a) Explain why some biologists think protecting keystone species
would help preserve biological diversity in an ecosystem. [1]
(b) Compare and contrast fundamental and realized niche of a
species. [2]
23. [Maximum mark: 5] 19M.2.SL.TZ1.14
The graph shows how the world rock phosphate production and world
population changed between 1900 and 2005.
[Source: Patrick D’ery and Bart Anderson]
(a) Describe the relationship between rock phosphate production
and world population. [2]
(b) Phosphate can be lost from agricultural land in several different
ways. State one of these. [1]
(c) Describe how the changes in world rock phosphate production
after 1985 may have affected world food supplies. [2]
24. [Maximum mark: 7] 19M.3.SL.TZ1.10
2
Torre Guaceto is a marine protected area which covers over 22 km of the
Adriatic Sea in south-eastern Italy. The diagram shows a food chain within this
area.
The data refers to the numbers of these three species inside the marine protected
area, where fishing is limited, and outside the marine protected area, where
fishing is allowed.
[Source: data provided by The Science of Marine Reserves Project (PISCO), based
on Guidetti 2006 Ecological Applications]
(a) State the trophic level of the sea urchin. [1]
(b) Compare and contrast the community structure within and
outside the marine protected area. [3]
(c) With respect to this food chain, outline what is meant by a
keystone species. [3]
© International Baccalaureate Organization, 2025
