Option C: Ecology and conservation (15/25 hours)

C1. Species and Communities

Use models as representations of the real world—zones of stress and limits of tolerance graphs are models of the real world that have predictive power and explain community structure. (1.10)

Theory of Knowledge

Random samples are taken in studies involving large geographical areas or if limited time is available. Is random sampling a useful tool for scientists despite the potential for sampling bias?


• The distribution of species is affected by limiting factors.
• Community structure can be strongly affected by keystone species.
• Each species plays a unique role within a community because of the unique combination of its spatial habitat and interactions with other species.
• Interactions between species in a community can be classified according to their effect.
• Two species cannot survive indefinitely in the same habitat if their niches are identical.

Applications and Skills

• Application: Distribution of one animal and one plant species to illustrate limits of tolerance and zones of stress.
• Application: Local examples to illustrate the range of ways in which species can interact within a community.

• Application: The symbiotic relationship between Zooxanthellae and reef-building coral reef species.

Zooxanthellae … what’s that? by NOAA

• Skill: Analysis of a data set that illustrates the distinction between fundamental and realized niche.

What is a niche? by FuseSchool

• Skill: Use of a transect to correlate the distribution of plant or animal species with an abiotic variable.

Coral Reef Fish Survey Simulation by NatGeo

Ecology Practical 2 – The distribution of species across a footpath by SAPS


Aim 6: Factors influencing herbivory could be investigated.

C2. Communities and Ecosystems

Use models as representations of the real world—pyramids of energy model the energy flow through ecosystems. (1.10)

Theory of Knowledge

Do the entities in scientists’ models, for example trophic levels or Gersmehl diagrams, actually exist, or are they primarily useful inventions for predicting and explaining the natural world?


• Most species occupy different trophic levels in multiple food chains.
• A food web shows all the possible food chains in a community.
• The percentage of ingested energy converted to biomass is dependent on the respiration rate.
• The type of stable ecosystem that will emerge in an area is predictable based on climate.
• In closed ecosystems energy but not matter is exchanged with the surroundings.
• Disturbance influences the structure and rate of change within ecosystems.

Applications and Skills

• Application: Conversion ratio in sustainable food production practices.
• Application: Consideration of one example of how humans interfere with nutrient cycling.
• Skill: Comparison of pyramids of energy from different ecosystems.

• Skill: Analysis of a climograph showing the relationship between temperature, rainfall and the type of ecosystem.

Create Climograph Data by USNA

• Skill: Construction of Gersmehl diagrams to show the inter-relationships between nutrient stores and flows between taiga, desert and tropical rainforest.

• Skill: Analysis of data showing primary succession.

• Skill: Investigation into the effect of an environmental disturbance on an ecosystem.

C3. Impacts of humans on ecosystems

Assessing risks and benefits associated with scientific research—the use of biological control has associated risk and requires verification by tightly controlled experiments before it is approved. (4.8)

International Mindedness

Over 100 countries across the globe have agreed to ban the production of CFCs to reduce the depletion of the ozone layer.


• Introduced alien species can escape into local ecosystems and become invasive.
• Competitive exclusion and the absence of predators can lead to reduction in the numbers of endemic species when alien species become invasive.
• Pollutants become concentrated in the tissues of organisms at higher trophic levels by biomagnification.
• Macroplastic and microplastic debris has accumulated in marine environments.

Human impacts on the environment by CrashCourse

Applications and Skills

• Application: Study of the introduction of cane toads in Australia and one other local example of the introduction of an alien species.

Introduction of cane toads in Australia by NationalMuseumAustralia

• Application: Discussion of the trade-off between control of the malarial parasite and DDT pollution.

Countries move toward more sustainable ways to roll back malaria by WHO


• Application: Case study of the impact of marine plastic debris on Laysan albatrosses and one other named species.

Ingestion of plastic debris by Laysan Albatrosses and Wedge-tailed Shearwaters in the Hawaiian Islands by ResearchGate

• Skill: Analysis of data illustrating the causes and consequences of biomagnification.
• Skill: Evaluation of eradication programmes and biological control as measures to reduce the impact of alien species.

Invaders! Game by PBS

Bug Hunt Predators and Invasive Species interactive model by NetLogo


Aim 8: Many developed countries export toxic waste to less developed countries. Is financial compensation a fair exchange for hazardous waste?

C4. Conservation and Biodiversity

Scientists collaborate with other agencies—the preservation of species involves international cooperation through intergovernmental and non-governmental organizations. (4.3)

Applications and Skills

• Application: Case study of the captive breeding and reintroduction of an endangered animal species.

Captive breeding by BBC

• Application: Analysis of the impact of biogeographic factors on diversity limited to island size and edge effects.

Effects of Biogeography on Community Diversity by NatureEducation

• Skill: Analysis of the biodiversity of two local communities using Simpson’s reciprocal index of diversity.

Simpson diversity index link

Biodiversity calculator by Virtue-s

Biodiversity calculator 2 by Alyoung




• An indicator species is an organism used to assess a specific environmental condition.
• Relative numbers of indicator species can be used to calculate the value of a biotic index.
• In situ conservation may require active management of nature reserves or national parks.
• Ex situ conservation is the preservation of species outside their natural habitats.
• Biogeographic factors affect species diversity.
• Richness and evenness are components of biodiversity.

⇒ Biome Viewer interactive  by HHMI


Aim 8: Scientists supported by governments are devoting relatively large amounts of effort to save particular animal species. Can criteria be established to justify a hierarchy of value of one species over another?

C5. Population ecology (AHL)

Avoiding bias—a random number generator helps to ensure population sampling is free from bias. (5.4)

International Mindedness

The issues around the growing global human population are of international concern regardless of different growth rates in different countries.


• Sampling techniques are used to estimate population size.
• The exponential growth pattern occurs in an ideal, unlimited environment.
• Population growth slows as a population reaches the carrying capacity of the environment.
• The phases shown in the sigmoid curve can be explained by relative rates of natality, mortality, immigration and emigration.
• Limiting factors can be top down or bottom up.

Population ecology by Bozeman

Applications and Skills

• Application: Evaluating the methods used to estimate the size of commercial stock of marine resources.
• Application: Use of the capture-mark-release-recapture method to estimate the population size of an animal species.

Capture-mark-release by EduMedia


• Application: Discussion of the effect of natality, mortality, immigration and emigration on population size.

Population Dynamics simulator by HHMI

 Human mortality database link


• Application: Analysis of the effect of population size, age and reproductive status on sustainable fishing practices.

• Application: Bottom-up control of algal blooms by shortage of nutrients and top-down control by herbivory.

Exploring Algal blooms by BBC


• Skill: Modelling the growth curve using a simple organism such as yeast or species of Lemna.

⇒ Exponential growth model interactive by NetLogo

Exponential & logistic growth by KhanAcademy


C6. Nitrogen andf Phosphorous cycles (AHL)

Assessing risks and benefits of scientific research—agricultural practices can disrupt the phosphorus cycle. (4.8)


• Nitrogen-fixing bacteria convert atmospheric nitrogen to ammonia.
• Rhizobium associates with roots in a mutualistic relationship.
• In the absence of oxygen denitrifying bacteria reduce nitrate in the soil.
• Phosphorus can be added to the phosphorus cycle by application of fertilizer or removed by the harvesting of agricultural crops.
• The rate of turnover in the phosphorus cycle is much lower than the nitrogen cycle.
• Availability of phosphate may become limiting to agriculture in the future.
• Leaching of mineral nutrients from agricultural land into rivers causes eutrophication and leads to increased biochemical oxygen demand.

Nitrogen cycle by FuseSchool

Nitrogen and Phosphorous cycles by CrashCourse

Applications and Skills

• Application: The impact of waterlogging on the nitrogen cycle.

• Application: Insectivorous plants as an adaptation for low nitrogen availability in waterlogged soils.
• Skill: Drawing and labelling a diagram of the nitrogen cycle.
• Skill: Assess the nutrient content of a soil sample.

Nutrient balanace by OECD

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