The image shows a transect through a stream and a field.

Which calculation would test for the association between two species of plants from quadrat data from section A and section B of the field?

A. Correlation coefficient

B. Random numbers sampling

C. Standard deviation

D. Chi-squared

D

What favours the production of peat?

I. Presence of organic matter

II. Anaerobic conditions

III. Acidic conditions

A. I and II only

B. I and III only

C. II and III only

D. I, II and III

D

Which processes occur in an ecosystem?

I. Biomass increases in each successive trophic level.

II. Inorganic nutrients are recycled.

III. Chemical energy is stored in carbon compounds.

A. I and II only

B. I and III only

C. II and III only

D. I, II and III 

C

What contributes to rising atmospheric concentrations of carbon dioxide and increases in average global temperature?

A. An increase in the shorter wavelength radiation emitted by Earth
B. An increase in longer wavelength radiation emitted by Earth
C. An increase in the combustion of fossilized organic matter
D. The depletion of ozone in the stratosphere

C

The diagram shows the food web for an aquatic ecosystem in which letters R–Z represent individual species.

[Source: © International Baccalaureate Organization 2019]

Which organism is a tertiary consumer?

A. Organism T

B. Organism U

C. Organism W

D. Organism Y

B

What is a potential consequence of the rise in global temperatures?

A. Increased exposure to UV light due to ozone depletion

B. Increase in ocean pH threatening the survival of marine organisms that require calcium carbonate

C. Decrease in the number and severity of storms due to the increased evaporation

D. Changes to circulating ocean currents

D

This was the only question where the percentage of candidates answering correctly dropped below the guess-level of 25 %. A and B were both more popular choices than the actual answer. A is incorrect because ozone depletion is not a cause of global warming. B is incorrect because increases in ocean pH are due to raised carbon dioxide concentrations, not global warming. It would clearly be prudent to assume that diploma candidates do not start the course with an understanding of the causes of the enhanced greenhouse effect, and this topic should therefore be taught thoroughly.

The three-toed sloth, Bradypus variegatus, lives in tree tops where it feeds on leaves. It also feeds on algae and fungi which live in its fur.

[Source: Image from https://commons.wikimedia.org/wiki/File:Bradypus_variegatus.jpg. Christian Mehlführer.
Licensed under CC by 2.5 https://creativecommons.org/licenses/by/2.5/deed.en]

In which trophic group should the three-toed sloth be classified?

A. Autotroph

B. Consumer

C. Detritivore

D. Saprotroph

B

Plankton are major producers in marine ecosystems. Only a small proportion of the energy harvested by plankton is passed to the primary consumers. Which process in phytoplankton results in the largest loss of energy that could otherwise be utilized by consumers?

A. Reproduction

B. Homeostasis

C. Excretion

D. Respiration

D

The global carbon cycle involves sinks where carbon is stored, and fluxes where carbon is transferred. What are the largest sink and flux?

C

In Topic 4.3 candidates had to estimate carbon fluxes due to processes in the carbon cycle. Candidates should have known that respiration and combustion return carbon dioxide to the atmosphere while photosynthesis uses this carbon dioxide. The total amount for the carbon dioxide released to the atmosphere is equal or smaller than the carbon dioxide absorbed, therefore eliminating answers A and B. Unfortunately, many capable candidates chose these options, making this question a bad discriminator. The ocean is by far the largest sink.

Deforestation and agricultural activities including the production of crops and livestock are thought to play a major role in the greenhouse effect. The graph shows annual trends in rates of deforestation and the production of soybeans and cattle in the state of Mato Grosso in Brazil in the period from 2001 to 2010.

[Source: 'Decoupling of deforestation and soy production in the southern Amazon during the late 2000s.'
Marcia N. Macedo, Ruth S. DeFries, Douglas C. Morton, Claudia M. Stickler, Gillian L. Galford, and Yosio E.
Shimabukuro PNAS January 24, 2012, 109 (4) 1341–1346; https://doi.org/10.1073/pnas.1111374109,
used with permission]

What conclusion can be drawn from the information in this graph?

A. The decline in rates of deforestation led to an increase in production of CO2.

B. Soybean production accounted for a greater proportion of deforestation than cattle production.

C. Forest habitats declined during the first few years of the study.

D. The decline in rates of deforestation is due to an increase in soybean production.

C

Candidates and some teachers found the graph complicated perhaps because of the twin y-axes and although the discrimination index was reasonable, fewer candidates answered correctly than had been anticipated. Answer A could be eliminated because no data on carbon dioxide production was supplied and D could also be eliminated because an increase in soybean production would if anything increase deforestation rates. Of the remaining two answers, fewer candidates chose the correct answer C than B. The graph shows that rates of deforestation increased between 2001 and 2003 so forest habitats will have declined during the first few years of the study. Presumably some candidates saw the increase on the graph and misinterpreted it as an increase in forest cover rather than in deforestation. The answer that most candidates chose was that soybean production accounted for a greater proportion of deforestation than cattle production. We cannot conclude this because the data provided is for production of soybeans and cattle and we do know what amounts of deforestation were involved in this production.

Which process contributes to the formation of limestone?

A. Partial decomposition of biomass in waterlogged soils

B. Fossilization of biomass in anaerobic conditions in waterlogged soils

C. Decomposition of soft tissues of marine animals in sea beds

D. Fossilization of hard parts from marine animals in sea beds

D

How is peat formed?

A. From methanogenic archaeans under anaerobic and acidic conditions in deep sea vents
B. From partially decomposed organic matter under anaerobic and acidic conditions in waterlogged soils
C. From porous limestone under high pressure, aerobic and alkaline conditions in ocean beds
D. From bituminous coal under high pressure, anaerobic and acidic conditions below ground

B

Hummingbirds eat flower nectar and small insects. To which nutritional group do they belong?

A. Autotrophs

B. Consumers

C. Detritivores

D. Saprotrophs

B

The table shows features of greenhouse gases in the atmosphere.

According to the data in the table, which greenhouse gas contributes the most to climate change?

A. Carbon dioxide because it is the most abundant greenhouse gas

B. Methane because it has the shortest lifespan

C. Nitrous oxides because they absorb the greatest amount of shortwave radiation

D. CFCs because they destroy the ozone layer

A

Very easy question with 93 % of candidates answering correctly.

The graph shows atmospheric oxygen levels over time.

About 2.5 billion years ago, a significant rise in atmospheric oxygen occurred. What was the cause of this rise?

A. Photosynthesis by non-vascular land plants

B. Photosynthesis by vascular land plants

C. Oxygen produced by photosynthetic bacteria being released from the ocean into the atmosphere

D. Volcanic activity

C

This question was based on the first Application in 2.9 (Photosynthesis) which requires a study of changes to the Earth's atmosphere due to photosynthesis. The graph shows the oxygenation of the atmosphere happening between 2.5 and 2 billion years ago. To answer the question correctly candidates had to choose which group of photosynthesizers were most likely to have caused this. Over 55 % correctly chose photosynthetic bacteria in the oceans, but large numbers also chose vascular land plants, including some of the stronger candidates. This group appeared less than 0.5 billion years ago. Detailed knowledge of the timings of plant evolution are not expected but students are expected to appreciate that the Great Oxygenation Event was due to prokaryotes photosynthesizing in the oceans.

Methanogens produce methane gas. What is this gas converted to in the atmosphere?

A. Carbon dioxide and oxygen

B. Ethanol and carbon dioxide

C. Carbon monoxide and ozone

D. Carbon dioxide and water

D

The diagram shows the carbon flux in gigatonnes per year between some of the Earth’s global reservoirs.

[Source: Figure 7.3 and Table 7.1 from Denman, K.L., G. Brasseur, A. Chidthaisong, P. Ciais, P.M. Cox, R.E. Dickinson, D.
Hauglustaine, C. Heinze, E. Holland, D. Jacob, U. Lohmann, S Ramachandran, P.L. da Silva Dias, S.C. Wofsy and
X. Zhang, 2007: Couplings Between Changes in the Climate System and Biogeochemistry. In: Climate Change
2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the
Intergovernmental Panel on Climate Change [Solomon, S., D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt,
M. Tignor and H.L. Miller (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.]

What can be deduced from the information in the diagram?

A. Arrows S are mainly due to respiration of marine plants and animals.

B. Photosynthesis is a component of both arrows Q and S.

C. Every day, more carbon is removed from the ocean than is added.

D. Ocean carbon is stored as dissolved calcium carbonate.

B