What is the ecological term for a group of different types of organisms that live together and interact with each other?

A. Community

B. Domain

C. Ecosystem

D. Population

A

Which conditions favour peat formation?

B

What restricts the length of a food chain?

A. Energy losses between the trophic levels
B. A greater biomass at the higher trophic levels
C. The number of species in the food web
D. The consumption of waste by detritivores

A

In the diagram, which of the processes labelled A to D transfers the largest mass of carbon per year in a woodland ecosystem?

[Source: © International Baccalaureate Organization 2019]

B

The Australian pitcher plant (Cephalotus follicularis) is a green plant that traps and feeds on flies and other live insects. What is this plant’s mode of nutrition?

A.  Producer and saprotroph

B.  Autotroph and detritivore

C.  Autotroph and heterotroph

D.  Consumer and saprotroph

C

Which organisms produce methane in anaerobic environments such as waterlogged soils?

A. Archaea

B. Fungi

C. Eukaryotes

D. Eubacteria

A

The diagram shows interactions between food chains in an ecosystem in the African savannah.

Which arrows indicate the flow of chemical energy?

A.  I and II only

B.  I and III only

C.  II and III only

D.  I, II and III

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

Which gases have made the most significant contributions to global warming?

A. Water and carbon dioxide

B. Carbon dioxide and methane

C. Methane and nitrous oxide

D. Carbon dioxide and ozone

A

Though most candidates opted for answer B (carbon dioxide and methane), the question discriminated well with the better students correctly giving response A (water and carbon dioxide). This should have been one of the easier questions as the required knowledge came directly from 4.4 in the guide (Climate change):

Carbon dioxide and water vapour are the most significant greenhouse gases.

Other gases including methane and nitrogen oxides have less impact.

The use of the term water rather than water vapour may have confused some candidates.

In an area of forest measuring 100 m by 100 m, samples were taken to estimate the number of silver maple (Acer saccharinum) trees in the forest. The number of trees counted in each of five areas of 400 m² was recorded.

Approximately how many silver maple trees are in the 10000m² area of forest?

A. 5

B. 25

C. 125

D. 625

C

What describes a possible cause of a negative carbon flux in the atmosphere due to processes occurring in a forest ecosystem?

A. The trees grew more so fixed more carbon dioxide.

B. There was more respiration by soil organisms.

C. There was more burning of forests.

D. There was more decomposition of leaf litter.

A

The bacterium Neisseria gonorrhoeae causes infections related to the human reproductive system. The graph shows the percentage of samples in which this bacterium showed resistance to six antibiotics over a period of ten years.

What is a possible explanation for the total percentage resistance being larger than 100% in 2010?

A. People do not take the antibiotics as prescribed.

B. More people have been sampled in that year.

C. There was an epidemic of Neisseria gonorrhoeae in that year.

D. Some bacteria are resistant to more than one antibiotic.

D

Cladograms can be created by comparing DNA or protein sequences. The cladogram on the left is based on DNA sequences and the cladogram on the right is based on comparing protein sequences.

What is the reason that cladograms based on DNA sequences are more reliable predictors of the phylogenetic relationship of species than cladograms based on protein sequences?

A. Amino acids are not as chemically stable as DNA nucleotides.

B. DNA mutates but amino acids do not.

C. Several different triplets of bases can code for the same amino acid.

D. There are 20 different amino acids but only 4 nucleotides.

C

In an ecosystem, in the transfer of carbon from producers to consumers, what is carbon transferred as?

I. Carbon dioxide

II. Protein

III. Hydrogencarbonate ions

A. I only

B. II only

C. I and II only

D. I and III only

B

Limpets are molluscs with conical shells that cling tightly to rocks on seashores. In a study of two species of limpets found on rocks along the Oregon coast, 30 randomly placed quadrats were used to determine how often the two species occurred together. The table shows the data that were collected.

Which statistical method will determine whether these two species occur together by chance or by some kind of interaction?

A.  Chi-squared test

B.  t-test

C.  Standard deviation

D.  Means and ranges

A

Which organism would be classified as a saprotroph?

A. A single-celled eukaryote that obtains its carbon compounds by photosynthesis and ingestion of other single-celled organisms

B. A jellyfish that uses the stinging cells in its tentacles to paralyse its prey, which is passed to an internal gastric cavity through a single opening

C. A fungus that feeds by secretion of digestive enzymes onto its food and absorption of digested material

D. A dung beetle that feeds on the fecal material left behind by other animals

C

What is lost between trophic levels in ecosystems and cannot be recycled?

A. Heat

B. Nitrogen

C. Carbon compounds

D. Biomass

A

The image shows a food web.

[Source: Adapted from Thompsma/Wikipedia]

Which organism in the food web is assigned to its method of nutrition?

A. A violet webcap fungus is both an autotroph and a heterotroph.

B. A pillbug is a secondary consumer.

C. Bacteria are saprotrophs.

D. A violet webcap fungus is a detritivore.

C

The oceans absorb much of the carbon dioxide in the atmosphere. The combustion of fossil fuels has increased carbon dioxide ocean concentrations. What adverse effect does this have on marine life?

A. Heterotrophs consume more phytoplankton.

B. Phytoplankton have increased rates of photosynthesis.

C. Corals deposit less calcium carbonate to form skeletons.

D. Increased pH reduces enzyme activity in marine organisms.

C

What material is formed when organic matter is not fully decomposed in acidic waterlogged soils?

A. Coal

B. Hydrogen

C. Oil

D. Peat

D

What is the classification of an organism that is able to make organic compounds from inorganic nutrients?

A. Autotroph
B. Consumer
C. Detritivore
D. Saprotroph

A

In a woodland ecosystem, each tree provides food for numerous aphids which feed on the sap of the tree. The aphids are eaten by carnivorous beetles, as shown in the food chain.

Oak Tree → Aphids → Beetles

Which pyramid of energy represents this relationship?

C

The table contains information about the diet of some animals.

Which pyramid of energy represents this information?

C

Euglena is a unicellular organism that feeds on bacteria and uses CO₂ as a carbon source. Which describes the nutrition of this organism?

A. Autotrophic only

B. Heterotrophic only

C. Saprotrophic only

D. Autotrophic and heterotrophic

D

The Venus flytrap (Dionaea muscipula) is a photosynthetic plant. It obtains nitrogen but not energy by digesting captured insects.

[Source: adapted from www.flytrapcare.com] 

Which term describes this plant?

A. Secondary consumer

B. Autotroph

C. Primary consumer

D. Saprotroph

B

Which level(s) of ecological complexity involve(s) biotic factors but not abiotic factors?

I. Community

II. Ecosystem

III. Population

A. I only

B. II only

C. I and II only

D. I and III only

D

Nearly 80 % of candidates answered this question correctly, despite it being multiple completion, which often causes difficulty. The relatively low discrimination index is expected when most candidates answer a question successfully. We can be pleased with questions such as this that widespread understanding of an aspect of biology is demonstrated. Here the understanding was of the differences between populations, communities and ecosystems.

Which activity directly contributes the most to recent increases in atmospheric CO₂ concentrations?

A. Landfills

B. Planting trees

C. Cattle rearing

D. Burning of fossil fuels

D

This was an easy question for most candidates with 89 % answering correctly.

In 1789 Gilbert White, a naturalist, observed eight breeding pairs of swifts (Apus apus) in the English village of Selborne. On average, each pair of swifts produces two offspring per year. This would allow the population to rise to 1030 swifts over 200 years. A bird survey carried out in 1983 revealed only 12 breeding pairs in this village.

What could have prevented the numbers rising to 1030?

I.   The number of nesting sites remained the same.

II.  The food supply of the swifts remained constant.

III. Predatory birds in the area were exterminated.

A.  I only

B.  I and II only

C.  II and III only

D.  I, II and III

B

How can a chi-squared test be used in ecological research?

A. To test the effect of an abiotic factor on one plant species

B. To test whether two species tend to live together

C. To test whether one population of plants is taller than another

D. To test whether one species is more tolerant to heavy metals than another

B

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 is not essential in a viable mesocosm?

A. Light source

B. Autotroph

C. Saprotroph

D. Herbivore

D

Which characteristic of water vapour classifies it as a greenhouse gas?

A. It absorbs and then re-emits some of the long wave radiation emitted by the Earth’s surface.

B. It prevents short wave radiation from reaching the Earth’s surface.

C. It absorbs UV radiation but does not re-emit it.

D. It absorbs infra-red radiation but does not re-emit it.

A

Over time, the hull of a sunken ship may become colonized by a wide range of marine organisms. What term is used to describe all of the organisms living in and on a sunken ship?

A. A community

B. An ecological niche

C. A population

D. An ecosystem

A

This question was criticised on G2 forms for being confusingly worded, but it had a good discrimination index and nearly 60 % of candidates answered correctly. The question asked about the animals around the sunken ship and not the ship as well, so the answer was community rather than ecosystem.

The Silver Springs feed into the Silver River in Florida. The diagram shows a pyramid of energy for the Silver Springs ecosystem. The units are kJ m^–2 y^–1.

[Source: © International Baccalaureate Organization 2019]

What do level I and level III represent in the pyramid of energy?

C

This question was easy, most candidates recognized that I was the producer and only a few believed II was a tertiary consumer instead of a secondary consumer.

The diagram shows the carbon cycle.

[Source: © International Baccalaureate Organization 2017]

Which two processes correspond to the labelled arrows?

A. K is combustion and L is catabolism.

B. J is anabolism and K is respiration.

C. J is combustion and K is respiration.

D. J is anabolism and L is catabolism.

C

How do greenhouse gases contribute to global warming?

A. They destroy the ozone layer, allowing radiation to reach the Earth’s surface.

B. They prevent radiation from the Earth escaping into space.

C. They trap short wavelength radiation in the atmosphere.

D. They are a product of combustion, which generates heat.

B

The discrimination index was high, but only a third of candidates answered correctly. A popular misconception was that greenhouse gases trap short-wave radiation. If that was the case, visible light from the sun would be unable to penetrate the Earth’s atmosphere.

The diagram shows a version of the carbon cycle. What is indicated by the numbers?

C

Which organism can best be described as a saprotroph?

A. A fungus that digests its food externally and absorbs the products of digestion

B. A beetle that feeds by ingesting the dung of other animal species and digesting its food internally

C. A single-celled eukaryote that is able to photosynthesize and consumes smaller organisms by endocytosis

D. A giraffe that feeds by ingesting leaves from an acacia tree

A

What is exchanged between a sealed mesocosm and the surrounding external environment?

A. Energy

B. Water

C. Air

D. Nothing can pass

A

This question had the lowest discrimination index on the paper so some well-prepared candidates must have answered it incorrectly. More than half of candidates thought that nothing can pass in or out of a sealed mesocosm, forgetting that energy will almost certainly be able to pass in or out in the form of heat and probably also in as light. In terms of thermodynamics, a closed system exchanges energy but not matter with its environment.

The diagram shows the energy flow between five “sinks” in a terrestrial ecosystem.

In a typical terrestrial ecosystem, which trophic level would have the highest biomass?

A. Autotrophs

B. Primary consumers

C. Secondary consumers

D. Detritus feeders

A

In addition to carbon dioxide, which of these greenhouse gases is the most significant?

A. Methane

B. Ozone

C. Nitrogen oxides

D. Water vapour

D

What is a community?

A. A group of individuals of the same species in a given area

B. A group of animals that interact socially

C. A group of organisms interacting with the abiotic environment

D. A group of populations interacting with each other within a given area

D

Animals in the highest trophic level of a food chain will often be the largest in body size but will be few in numbers. What accounts for the small numbers?

A. Food eaten by animals at the highest trophic level has a lower energy content per gram

B. Energy losses through the food chain

C. Conversion of heat energy into chemical energy

D. Biomass of producers is small

B

By which mechanism do greenhouse gases contribute to global warming?

A. Their higher concentration absorbs more long wave radiation coming from the Sun.

B. Short wave radiation emitted from the Earth’s surface increases with their concentration.

C. They absorb higher amounts of long wave radiation emitted from the Earth’s surface as their concentration increases.

D. They absorb higher amounts of short wave radiation caused by increased combustion of fossilized organic matter.

C

The diagram shows the flow of energy through an ecosystem in ${\text{kJ\hspace{0.05em}m}}^{–2}{\text{\hspace{0.05em}y}}^{–1}.$

[Source: “Energy flow: Figure 3,” (https://cnx.org/contents/[email protected]:fbNheNoN@8/Energy-Flow) by OpenStax College, Biology CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/).]

What percentage of the energy passed from primary producers to primary consumers is lost to cellular respiration by tertiary consumers?

A. 0.001%

B. 0.08%

C. 0.2%

D. 0.4%

D

The candidates found this question difficult, possibly because the arrow coming from the primary producers shows 40 000 kJ m⁻² y⁻¹ leaving but only half of that is taken up by primary consumers, the remainder being lost to saprotrophs and detritivores. Some G2 forms suggested that the calculation was too difficult without the aid of a calculator but if the candidates had chosen the correct values from the diagram the calculation would have been straightforward ($80 \times \frac{100}{20 000}=0.4 \%$).

The diagram shows a simplified carbon cycle.

Which processes are taking place at X and Y?

D

The diagram shows part of a food chain. The left box represents producers and the right box primary consumers. Arrows show energy flows.

Which forms of energy are represented by X and Y?

D

Some centres thought the diagram was difficult to interpret but the question did discriminate well showing the better students had the ability to adapt.

Under certain conditions, living organisms on Earth produce and release methane. What favours the production of methane?

A. Forest fires

B. High light intensity

C. Anaerobic conditions

D. Dry conditions

C