6.2 CLIMATE CHANGE: CAUSES AND IMPACTS

📌 Definitions Table

Term	Definition (Exam-Ready, 2 Marks)
Industrial Revolution	A period of rapid industrial growth beginning in the 18th century, marked by increased fossil fuel use and greenhouse gas emissions.
Proxy Data	Indirect evidence (e.g., ice cores, tree rings) used to reconstruct past climate conditions in the absence of direct measurements.
Albedo	The proportion of incoming solar radiation reflected by a surface; high albedo surfaces (like ice) reflect more sunlight.
Little Ice Age	A period of cooler global temperatures from roughly the 14th to 19th centuries, with regional climate impacts.
Planetary Boundaries Model	A framework identifying limits within which humanity can safely operate to avoid destabilizing Earth system processes.
Vector-Borne Diseases	Diseases transmitted by vectors such as mosquitoes or ticks, often influenced by climate and environmental changes.

• 🧠 Exam Tips:
  
  Use dates and impacts when defining historical periods like the Industrial Revolution or Little Ice Age.
  
  Connect albedo and planetary boundaries to climate regulation and system stability for stronger answers.

📌 Atmospheric Processes Affecting Climate

• Climate describes the typical conditions resulting from various physical processes in the atmosphere

Atmospheric Processes Affecting Climate

Process	Explanation
Solar radiation	Energy from sun reaches Earth’s surface, varying in intensity due to Earth’s tilt and rotationHeats equator more intensely than poles, creating temperature gradientsInitiates atmospheric processes such as atmospheric circulation and convection currents
Atmospheric circulation	Movement of air driven by solar heating and Earth’s rotation, creating global wind patterns (Hadley, Ferrel and Polar cells), which transport heat and moisture
Convection currents	Vertical movement of air due to temperature differences, creating weather phenomena (e.g. thunderstorms and tropical cyclones)
Condensation and cloud formation	Atmospheric water vapour cools and condenses into liquid droplets or ice crystalsForms clouds that affect weather by reflecting sunlight and trapping infrared radiation
Precipitation	Water droplets or ice crystals fall from clouds as rain, snow, sleet, or hail, depending on temperature and atmospheric conditions
Evaporation	Conversion of water from liquid to vapour phase due to heat, which then rises into the atmosphere
Greenhouse effect	Natural process where atmospheric gases in trap heat from sun, making Earth’s temperature suitable for lifeAnthropogenic activities increase concentration of greenhouse gasesEnhances greenhouse effect, increases average annual temperatures and impacts many of the atmospheric processes outlined above

• The main factors influencing climate are seasonal variations in temperature and precipitation
• These variations shape the long-term climate patterns of a region

📌 Causes of Climate Change

🌐 EE Tip: Analyze historical climate data (e.g., temperature or CO₂ trends) and assess the local impacts or responses.

Anthropogenic influence on climate

• Human activities have significantly increased atmospheric concentrations of greenhouse gasessince the Industrial Revolution
  • Particularly carbon dioxide emissions from burning fossil fuels
• This has led to:
  • Global warming: average global temperatures have risen due to enhanced greenhouse effect
  • Climate change: altered weather patterns, sea level rise and impacts on ecosystems and human societies

Global rate of emissions

• Since 1950, the rate of anthropogenic carbon dioxide emissions has significantly accelerated
  • This acceleration is due to several factors, including:
• Industrial Revolution:
  • It began in the late 18th century in Europe
  • Marked a turning point with the widespread use of fossil fuels such as coal and later oil
• Technological advancements:
  • The 20th century saw rapid industrialisation, transportation development and urbanisation
  • These all contributed to increased emissions
• Population growth:
  • The global population has increased exponentially
  • This has increased demand for energy and resources, further accelerating emissions

Analysis of ice cores, tree rings and sediments

• Ice cores, tree rings and sediment deposits provide important data for understanding:
  • Historical climate patterns
  • The relationship between carbon dioxide levels and global temperatures
• Ice cores:
  • Layers of ice in glaciers trap air bubbles containing the gases from ancient atmospheres
  • Analysis of these bubbles shows historical carbon dioxide levels
    • Ice is deposited as water freezes over time, so the deeper into the ice you go, the older it is

• Tree rings:
  • Trees form annual rings with varying widths based on climate conditions
    • Thicker rings indicate favourable (warmer) conditions, potentially linked to higher carbon dioxide levels
  • Analysis of the width of tree rings can provide a measure of climate during each year of growth
  • Taking cores from the trunks of older trees can provide samples that go back over hundreds of years

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• Sediments:
  • Deposits in lakes and oceans contain remains of organisms sensitive to environmental changes
    • This provides indirect evidence of past climates

Positive correlation between carbon dioxide and global temperatures

• Research using data from these sources shows a clear positive correlation between atmospheric carbon dioxide concentrations and global temperatures
  • Carbon dioxide levels: as industrial activities have increased, so have atmospheric carbon dioxide levels
  • Temperature records: proxy data from ice cores, tree rings and other sources indicates that periods with higher carbon dioxide concentrations correspond to warmer global temperatures
  • Modern instrumental records: direct measurements since the mid-20th century confirm a sharp rise in temperatures, aligning with increased emissions
• Since the Industrial Revolution, atmospheric carbon dioxide levels have risen to their highest in Earth’s history
  • Before, the highest atmospheric carbon dioxide concentration was around 300 parts per million (ppm)
  • It is currently above 400 ppm

• Data show a correlation between changing atmospheric carbon dioxide levels and temperature over thousands of years
  • Correlation does not equal causation
  • However, this is convincing evidence supporting the hypothesis that carbon dioxide emissions from human activity are driving up global temperatures

Average global temperatures

• Thermometers can be used to measure air temperature
• Records from the mid-1800s show an overall trend of increasing average global temperatures
  • There are some short time periods within this window during which temperatures have declined, but the overall trend is upward
• The time period since the mid-1800s corresponds with the time during which humans have been burning fossil fuels

• 90% of global carbon dioxide emissions come from industry and burning fossil fuels
  • As carbon dioxide, methane and water vapour are released, they act as greenhouse gases andtrap heat within the Earth’s atmosphere
  • Human activities are responsible for almost all of the increase in greenhouse gases in the atmosphere over the last 150 years

The enhanced greenhouse effect

• The enhanced greenhouse effect is different from the natural greenhouse effect
  • It is the result of human activities that release excessive greenhouse gases into the atmosphere
  • This leads to an intensified trapping of heat and results in global warming
• The natural greenhouse effect is a necessary process
  • It helps regulate the Earth’s temperature by trapping some heat to maintain a habitable climate
• The enhanced greenhouse effect disrupts this balance as a result of greenhouse gas concentrations being artificially increased beyond natural levels

Modelling climate change

Systems diagrams and models

• Representing cause and effect:
  • Systems diagrams and models are tools that can be used to visualise how different factors interact and cause climate change
  • They help us understand cause-and-effect relationships and how changes in one part of the system affect others

Feedback loops

• Feedback loops are processes that can either amplify or dampen the effects of climate change
  • Positive feedback loops amplify changes
  • Negative feedback loops reduce or counteract changes
• Global energy balance:
  • The global energy balance is the balance between the energy Earth receives from the Sun and the energy it radiates back into space
  • Changes in this balance can significantly impact the climate

Changes in solar radiation and terrestrial albedo

• Solar radiation is the primary source of energy for Earth’s climate system
• Variations in solar radiation can lead to changes in climate
  • For example, the Maunder Minimum (1645–1715), a period with very few sunspots, was associated with cooler global temperatures
• Changes in solar radiation can initiate feedback loops
  • Decrease in solar radiation: can cause cooling, leading to an increase in snow and ice cover
    • This increases the Earth’s albedo, causing further cooling (negative feedback loop)
    • For example, during the Maunder Minimum, reduced solar radiation contributed to the Little Ice Age
  • Increase in solar radiation: can cause warming, reducing snow and ice cover
    • This decreases the Earth’s albedo, causing further warming (positive feedback loop)

Carbon dioxide and methane release

• Carbon dioxide and methane are greenhouse gases
• Carbon dioxide and methane get trapped in permafrost as organic matter freezes before it can fully decompose
• Positive feedback loop:
  • When the permafrost thaws due to warming temperatures, these trapped gases are released into the atmosphere
  • These greenhouse gases then contribute to further global warming and climate change

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Crossing the planetary boundary for climate change

• Climate change is one of the nine planetary boundaries outlined by the planetary boundaries model
  • Planetary boundaries are thresholds that lead to significant environmental changes if they are crossed
• Evidence suggests Earth has alreadycrossed the boundary for climate change
  • The Intergovernmental Panel on Climate Change (IPCC) is a leading authority on climate science
  • IPCC reports provide comprehensive assessments of climate change, based on the latestscientific research
  • These reports show:
    • Significant increases in global temperatures:
      • Over the past century, the average global temperature has risen by approximately 1.1 °C
      • The most rapid warming has occurred in recent decades
    • Rising greenhouse gas concentrations:
      • Levels of carbon dioxide and methane in the atmosphere have increased dramatically
      • Due to human activities like burning fossil fuels, deforestation and agriculture,
    • Current impacts:
      • These changes contribute to more frequent and intense extreme weather events, such as heatwaves, storms and flooding
      • As well as long-term effects like rising sea levels and shifting ecosystems

📌 Impacts of Climate Change on Ecosystems

• Climate change:
  • Impacts ecosystems on various scales, from local to global
  • Affects the resilience of ecosystems
  • Leads to biome shifts

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Local impacts

Coral bleaching

• Cause:
  • Increased sea temperatures cause corals to expel the algae (zooxanthellae) living in their tissues
  • Without these algae, corals lose their colour (giving them a white appearance)
  • They also lose their main food source (the algae perform photosynthesis, producing organic compounds that the corals use as a primary energy source)
  • This leads to bleaching and eventually coral death
• Effects:
  • Loss of biodiversity as fish and other marine species lose their habitat
  • Decline in fish populations in reef ecosystems
• Example:
  • The Great Barrier Reef in Australia has experienced significant coral bleaching events

Desertification

• Cause:
  • Prolonged droughts and higher temperatures
  • Unsustainable land practices like deforestation and overgrazing
• Effects:
  • Loss of arable land and vegetation, leading to soil erosion
  • Reduced agricultural productivity
  • Displacement of communities
• Example:
  • The Sahel region in Africa is facing severe desertification, affecting local livelihoods that rely on agriculture

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Global impacts

Changes to ocean circulation

• Cause:
  • Melting ice caps and glaciers increase the freshwater input into oceans
  • This disrupts normal currents and circulation patterns
• Effects:
  • Altered weather patterns
  • Changes in marine and coastal ecosystems
  • Changes in fish migration and distribution affecting fisheries
• Example:
  • Slowing down of Atlantic Meridional Overturning Circulation (AMOC), which includes the Gulf Stream
  • This is leading to colder winters in Europe and warmer temperatures in the Arctic

Sea-level rise

• Cause:
  • Melting ice caps and glaciers
  • Thermal expansion of seawater due to higher temperatures
• Effects:
  • Coastal flooding and erosion, impacting ecosystems like mangroves and salt marshes
  • Loss of habitats for species in these biodiverse ecosystems
• Example:
  • The Maldives is at risk of becoming uninhabitable due to rising sea levels

Regional impacts on natural productivity

Increased productivity

• Northern regions:
  • Warmer temperatures can extend the growing season and increase vegetation
  • Expansion of suitable areas for agriculture and forestry
  • For example, in parts of Canada and Russia, agriculture is expanding northward and growing seasons are longer due to warmer conditions

Decreased productivity

• Tropical regions:
  • Higher temperatures and unpredictable rainfall can harm crops
  • For instance, shifting monsoon patterns in Southeast Asia are threatening rice yields

Factors affecting ecosystem resilience

Biodiversity

• Climate change can reduce resilience by decreasing biodiversity
• High biodiversity:
  • Increases resilience by providing a variety of species that can adapt to changes
  • For example, tropical rainforests have high biodiversity, helping them recover from disturbances
• Low biodiversity:
  • Decreases resilience, making ecosystems more vulnerable
  • For example, monoculture farms are less resilient to pests and diseases
• Impact of climate change:
  • Climate change can lead to habitat loss, altered food webs and extreme weather events
  • All of these can reduce biodiversity
    • For example, coral bleaching due to increased sea temperatures reduces the variety of species in coral reefs
    • This can reduce the resilience of coral reefs to other stressors, like ocean acidification or increased tropical storms

Habitat fragmentation

• Climate change can also reduce resilience by causing habitat fragmentation
• Connected habitats:
  • Enable species to migrate and adapt to changes
• Fragmented habitats:
  • Isolate species and split populations, reducing their ability to adapt
• Impact of climate change:
  • Rising temperatures and changing precipitation patterns can shift habitats, leading to fragmented landscapes
  • Climate change can fragment habitats in various ways:
    • Increased desertification: expanding deserts can divide ecosystems, making it harder for species to find resources and migrate
    • Increased rates of forest fires: more frequent and intense fires can break up forest ecosystems, isolating populations and reducing biodiversity
    • Melting polar ice caps: loss of ice habitats can fragment the habitats of polar species like polar bears and penguins, affecting their ability to hunt and reproduce
    • Species in mountainous regions might be forced to move to higher altitudes, creating isolated populations
• These changes reduce the resilience of ecosystems by isolating species and limiting their ability to adapt to new conditions

Biome shifts

• Climate change:
  • Impacts ecosystems on various scales, from local to global
  • Affects the resilience of ecosystems
  • Leads to biome shifts

📌 Impacts of Climate Change on Societies

• Climate change impacts human societies at various scales and socio-economic conditions
  • This means that the impacts of climate change affect societies differently based on their:
    • Economic status
    • Resources
    • Social conditions
  • Socio-economic conditions include factors like:
    • Income levels
    • Access to resources
    • Quality of infrastructure
    • Education
    • Healthcare availability
• Impacts of climate change also affect the resilience of societies

🔍 TOK Tip: What role does media play in shaping public knowledge of atmospheric science?

Key impacts of climate change

• Key areas of societies that are impacted include health, water supply, agriculture and infrastructure

Health impacts

• Heatwaves:
  • Increased frequency and intensity
  • These can be especially dangerous for the young and elderly
  • E.g. the North American Heatwave 2021:
    • A severe and prolonged heatwave hit the Pacific Northwest region of the United States and Western Canada in June 2021
    • The extreme heatwave led to:
      • Hundreds of deaths across the region
      • Overwhelmed hospitals with cases of heat-related illnesses
      • Caused power outages as electrical grids struggled to cope with increased demand for air conditioning
• Diseases:
  • Warmer temperatures expand habitats for disease-carrying insects
  • Leads to spread of vector-borne diseases like malaria and dengue to new areas
• Air quality:
  • Poor air quality due to higher temperatures and pollutants:
    • Higher temperatures can enhance the formation of ground-level ozone, a harmful air pollutant
    • More frequent and severe wildfires release large amounts of smoke and particulate matter into the air
    • Climate change can lead to more frequent stagnant air conditions, which prevent pollutants from dispersing

Water supply impacts

• Droughts:
  • Longer and more severe droughts reduce water availability
  • E.g. Cape Town’s Day Zero water crisis in 2018
• Melting glaciers:
  • Reduces freshwater availability for downstream communities
  • E.g. glaciers in the Andes are melting, threatening water supplies in South America
• Flooding:
  • More intense rainfall leads to flooding
  • Flooding can contaminate drinking water sources with pollutants, sewage and hazardous chemicals, making the water unsafe to drink
• Water Quality:
  • Combined with nutrient pollution (e.g. from agricultural runoff), warmer water temperatures promotes the growth of harmful algal blooms
  • These blooms produce toxins that can contaminate drinking water
  • E.g. algal blooms in Lake Erie in North America have repeatedly made the water unsafe for consumption

Agriculture impacts

• Crop yields:
  • Changes in temperature and rainfall affect crop production
  • E.g. reduced wheat yields in Australia and India due to heat stress
• Pest outbreaks:
  • Warmer climates increase the prevalence of agricultural pests
• Food security:
  • Less reliable food supply and higher prices
• Livestock:
  • Heat stress affects livestock health and productivity
  • E.g. heat stress in dairy cows decreases their milk yield

Infrastructure impacts

• Extreme weather:
  • More frequent hurricanes, floods and storms damage infrastructure
• Transportation:
  • Roads and railways damaged by extreme weather
  • E.g. UK railways have been disrupted by flooding and heat in recent years
• Buildings:
  • Increased costs for cooling
  • Increased cost of repairs from storm damage
  • Coastal erosion damages properties on seafronts
• Energy supply:
  • Power outages from extreme weather affecting grids

Resilience of societies

• Resilience refers to a society’s ability to withstand, adapt to and recover from climate change impacts
  • Different factors contribute to the resilience of societies, including economic stability, social equity and adaptive capacity
• Economic stability:
  • Economic resources are crucial for repairing and rebuilding after climate-related disasters
  • E.g. the cost of rebuilding after hurricanes can strain local economies, but wealthier regions have more resources to recover quickly
• Social equity:
  • Vulnerable communities, such as low-income or marginalised groups, are often more severely affected by climate change
• Adaptive capacity:
  • The ability to adapt to climate change varies significantly between regions and countries
  • E.g. the Netherlands has advanced flood defences, while Bangladesh remains highly vulnerable to flooding due to limited resources

• Individual experiences, societal values, and policies all influence perspectives on climate change
  • These perspectives shape how people and societies respond to climate challenges

Individual perspectives

• People’s own experiences with climate change shape their awareness and concern
  • For example, farmers noticing changes in growing seasons may be more aware of climate impacts than urban residents

• Individuals can take personal steps to mitigate their contributions to climate change
  • E.g. by reducing their carbon footprint, such as using public transport or reducing energy consumption
• Personal health concerns may influence perspectives on climate action
  • E.g. parents in polluted urban areas may be concerned about children’s asthma

Societal perspectives

• Government policies play an important role in mitigating and adapting to climate change
  • E.g. UK’s commitment to net-zero carbon emissions by 2050
• Local communities often take initiatives to enhance resilience and reduce climate impacts
  • E.g. urban community gardens may help to improve food security and reduce heat island effects
• Cultural values and traditions influence how societies perceive and respond to climate change
  • For example, indigenous communities may incorporate traditional ecological knowledge into their adaptation strategies
  • This might include adjusting agricultural practices based on seasonal changes observed over many generations

6.1 INTRODUCTION TO THE ATMOSPHERE

📌 Definitions Table

Term	Definition
Biosphere	The global system that includes all living organisms and their interactions with the atmosphere, lithosphere, and hydrosphere.
Greenhouse Effect	The natural process where greenhouse gases trap heat in the Earth’s atmosphere, maintaining suitable temperatures for life.
Stratification	The layering of water in lakes or oceans due to differences in temperature, salinity, or density, which limits mixing.
Tricellular Model of Atmospheric Circulation	A model describing three large-scale circulation cells (Hadley, Ferrel, Polar) in each hemisphere that distribute heat and moisture globally.
Sublimation	The phase change of a substance directly from solid to gas without passing through the liquid state (e.g., ice to vapor).
Rice Paddies	Flooded fields used for growing rice, often associated with methane emissions due to anaerobic decomposition.

• 🧠 Exam Tips:
  
  In climate-related terms, always connect process to environmental function or impact (e.g., “traps heat,” “distributes moisture”).
  
  For rice paddies, mention greenhouse gas link when relevant to climate change questions.

📌 Atmospheric Composition and Function

• The atmosphere forms the boundary between Earth and space
• It is the outer limit of the biosphere
• The atmosphere supports life on Earth

Atmospheric gases and their redistribution

• The atmosphere is mainly composed of nitrogen (about 78%) and oxygen (about 21%)
  • These two gases make up the majority of the atmosphere and play vital roles in supporting life on Earth
• The atmosphere contains smaller amounts of other gases, including:
  • Carbon dioxide
  • Argon
  • Water vapour
  • Various trace gases
• Carbon dioxide, although present in relatively low concentrations (around 0.04%), is essential for:
  • Photosynthesis in plants
  • Maintaining the greenhouse effect
• Argon is an inert gas that does not participate in chemical reactions but contributes to the overall composition of the atmosphere
• Water vapour plays an important role in:
  • Photosynthesis in plants
  • The Earth’s weather patterns
  • The formation of clouds and precipitation
• Trace gases, such as methane, ozone, and nitrous oxide, are present in even smaller quantities
  • However, they still have significant impacts on climate and atmospheric chemistry

Redistribution through physical processes

• Gases in the atmosphere are moved around by various physical processes, including:
  • Wind: the main mover of gases, caused by differences in air pressure
  • Convection: warm air rises and cool air sinks, creating vertical movement
  • Diffusion: gases spread from areas of high concentration to areas of low concentration
  • Turbulence: irregular air flow caused by obstacles like mountains and buildings
  • Jet streams: fast-flowing, narrow air currents in the upper atmosphere

Atmospheric layers

• Atmospheric stratification:
  • The atmosphere is divided into layers based on temperature changes
  • The key layers for living systems are the troposphere and the stratosphere
• Troposphere:
  • The lowest layer, extending up to about 10 km from the Earth’s surface
  • Weather phenomena, such as clouds, precipitation, and gas mixing, occur here
  • Contains the highest concentration of water vapour, carbon dioxide and other important trace gases
• Stratosphere:
  • Located above the troposphere, extending from about 10 to 50 km above the Earth’s surface
  • Contains the ozone layer, which absorbs and blocks most of the Sun’s harmful ultraviolet (UV) radiation
• Importance of inner layers:
  • Various reactions in the troposphere and stratosphere are vital for maintaining the balance of gases, regulating climate and supporting life
  • In the troposphere, chemical reactions involving pollutants, greenhouse gases and particles impact air quality and climate
  • In the stratosphere, chemical reactions involving ozone maintain the ozone layer and protect organisms on Earth from harmful UV radiation

Differential heating and the tricellular model

• Differential heating of the atmosphere:
  • The Sun heats the Earth and its atmosphere unevenly
  • The equator receives more direct sunlight, making it warmer
  • The poles receive less direct sunlight, making them cooler
  • This results in an effect known as the tricellular model of atmospheric circulation
    • This model explains how heat is distributed from the equator to the poles

Atmospheric systems

• The atmosphere is a highly dynamic system
  • It plays a crucial role in the Earth’s climate and weather patterns
  • As with other systems, the atmospheric system is made up of storages, flows, inputs and outputs
• Storages:
  • The atmosphere acts as a storage for gases
  • These gases are present in different concentrations
  • These concentrations can vary over time due to natural and human activities
  • This includes greenhouse gases like carbon dioxide and methane
    • These gases contribute to the greenhouse effect and influence the Earth’s temperature
• Flows:
  • Within the atmosphere, there are constant flows of gases and particles
  • These flows are driven by processes such as air currents, weather patterns and atmospheric circulation
  • These flows contribute to the movement and redistribution of gases and other substances within the atmosphere
• Inputs:
  • The atmosphere receives inputs from various sources
  • Natural inputs include:
    • Gases emitted from volcanic eruptions
    • Gases emitted from plants and other living organisms
    • Dust particles from desert regions
  • Anthropogenic inputs, resulting from human activities, include:
    • Greenhouse gases (e.g. from fossil fuel combustion and livestock)
    • Air pollutants from industrial processes
    • Aerosols from combustion

• Outputs:
  • Gases maybe be removed from atmospheric systems through natural processes like respirationand photosynthesis
  • Pollutants and aerosols can be removed from the atmosphere through, e.g. precipitation and dry deposition
• Exchanges and interactions with other Earth systems:
  • The atmosphere interacts with other components of the Earth system
    • This includes the biosphere (plants, animals, and microorganisms), hydrosphere (oceans, lakes, and rivers), and lithosphere (landmasses and rocks)
  • It exchanges gases and particles with these systems through various mechanisms
    • E.g. the exchange of carbon dioxide occurs through photosynthesis by plants and respiration by organisms
  • These interactions involve the exchange of gases, energy and particles
    • This shapes climate patterns, weather events and overall Earth system dynamics

📌 The Greenhouse Function

• Greenhouse gases (GHGs) and aerosols play an important role in Earth’s climate by trapping heat in the atmosphere

Greenhouse gases and aerosols

• GHGs: gases in the atmosphere that trap heat
  • Key GHGs:
    • Water vapour
    • Carbon dioxide
    • Methane
    • Nitrous Oxides
• Aerosols: tiny particles or droplets in the atmosphere
  • Key aerosols:
    • Black carbon
      • A type of aerosol produced from incomplete combustion of fossil fuels, wood and other biomass
      • Found in emissions from, e.g. diesel engines, cooking stoves and open burning of vegetation
      • Absorbs sunlight and warms the atmosphere
      • Can darken snow and ice surfaces, reducing their reflectivity and accelerating melting

Key Greenhouse Gases

Name of GHG	Sources	Other Information
Water vapour	Evaporation from oceans, lakes and riversTranspiration from plantsSublimation from ice and snowCombustion of fossil fuels	Most abundant GHGConcentration varies with temperatureAmplifies effects of other GHGsPositive feedback loop: warmer atmosphere holds more water vapour, leading to more warming and greater evaporationIt is often excluded from climate models due to its dynamic levels and essential role in life, meaning it cannot be mitigated against
Carbon dioxide	Burning fossil fuels: coal, oil and natural gas (e.g. vehicle emissions)Deforestation (when forests are cleared or burned, the carbon stored in trees is released back into atmosphere as carbon dioxide)Industrial processes (e.g. cement production)	Significant contributor to the greenhouse effect due to high concentration and long lifespan in the atmosphere
Methane	Agriculture: livestock digestion (e.g. from large-scale cattle farming)LandfillsNatural gas extraction (methane leaks)rice paddiesWetlands	More effective at trapping heat than carbon dioxide (over 20 times more potent over 100 years)Found in much lower concentrations than carbon dioxide, so overall warming effect is less
Nitrous oxides	Agricultural practices (use of synthetic and organic fertilisers)Fossil fuel combustionIndustrial processes	Potent GHG with a warming effect nearly 300 times that of carbon dioxide per moleculeFound in much lower concentrations than carbon dioxide, so overall warming effect is less

What is the greenhouse effect?

• The Sun emits energy in the form of solar radiation
  • This includes visible light and ultraviolet rays
• This solar radiation enters the Earth’s atmosphere
• Some thermal energy is reflected from the Earth’s surface
• Most thermal energy is absorbed and re-emitted back from the Earth’s surface
  • This energy passes through the atmosphere
• Some thermal energy passes straight through and is emitted into space
• However, some thermal energy is absorbed by greenhouse gases
  • This causes thermal energy to be re-emitted in all directions
• These gases act like a blanket
  • They allow sunlight to pass through while preventing a significant amount of the infrared radiation from escaping back into space
• This reduces the thermal energy lost into space and traps it within the Earth’s atmosphere
  • This keeps the Earth warm
• This process is known as the greenhouse effect
  • The greenhouse effect is a naturally occurring phenomenon
  • The greenhouse effect is important to ensure that Earth is warm enough for life
  • Without the greenhouse effect, the average temperature would be much colder, making the planet uninhabitable
    • For example, the average surface temperature of Earth is about 15 °C
    • Without the greenhouse effect, it would be about -18 °C

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📘 Key Concepts and Definitions

Term	Definition
Animal Research	The scientific use of non-human animals to investigate biological and psychological processes relevant to human behaviour.
Translational Research	Research using animal models to understand mechanisms that can be applied to human conditions (e.g., stress, learning, memory).
Comparative Psychology	The study of similarities and differences in behaviour across species to infer evolutionary and biological principles.
Ethological Validity	The extent to which animal research reflects natural animal behaviour, ensuring ecological accuracy.
3Rs Principle	Ethical framework for animal research — Replacement, Reduction, Refinement.
Extrapolation	Applying results from animal studies to humans, assuming shared biological mechanisms.
Lesion Studies	Intentional damage or stimulation of specific brain areas in animals to study behaviour changes.
Enrichment	Providing stimulating environments for laboratory animals to enhance well-being and validity.

📘 Core Studies

1. Rosenzweig, Bennett, & Diamond (1972)

• Aim: Investigate whether environmental factors (enriched or deprived) affect neuroplasticity in the cerebral cortex of rats.
  
• Method: Rats were placed in enriched or deprived conditions for 30–60 days; cortical thickness measured post-mortem.
  
• Findings: Enriched environment rats had thicker cortices and higher acetylcholinesterase activity.
  
• Conclusion: Stimulation influences synaptic growth — demonstrating neuroplasticity.
  
• Evaluation:
  
  • ✅ Strengths: Controlled lab design; replicable; established cause–effect link.
    
  • ⚠️ Limitations: Limited generalizability; ethical concern over euthanasia.
    

2. Rogers & Kesner (2003)

• Aim: Examine acetylcholine’s role in spatial memory using rats.
  
• Method: Rats trained to find food in a maze; injected with scopolamine (ACh blocker).
  
• Findings: Scopolamine group took longer and made more errors.
  
• Conclusion: Acetylcholine is essential for memory formation.
  
• Evaluation:
  
  • ✅ Strength: Demonstrated neurotransmitter function under controlled conditions.
    
  • ⚠️ Limitation: Translational gap — human cognition is more complex.
    

3. Sapolsky (1990s–2005)

• Aim: Investigate stress physiology in wild baboons to model human stress responses.
  
• Findings: Dominance hierarchies affected cortisol levels; low-ranking baboons had chronically high cortisol, paralleling human stress-related disorders.
  
• Evaluation:
  
  • ✅ Strength: Naturalistic validity; long-term field observation.
    
  • ⚠️ Limitation: Causality unclear; ethical concerns over observation of suffering.
    

4. Harlow (1958)

• Aim: Study the importance of comfort contact in attachment.
  
• Method: Infant rhesus monkeys given wire or cloth “mothers.”
  
• Findings: Monkeys preferred soft cloth mothers, even without food.
  
• Conclusion: Attachment is based on comfort, not feeding.
  
• Evaluation:
  
  • ✅ Strength: Groundbreaking insight into emotional bonding.
    
  • ⚠️ Limitation: Severe psychological harm; modern ethics would not approve.
    

5. Martinez & Kesner (1991)

• Aim: Determine the role of acetylcholine in memory formation in rats.
  
• Method: Rats injected with scopolamine or physostigmine (ACh enhancer) before maze learning.
  
• Findings: Scopolamine impaired, while physostigmine improved memory.
  
• Conclusion: ACh crucial for encoding memory.
  
• Evaluation:
  
  • ✅ Strength: Controlled and replicable; biological mechanism clarified.
    
  • ⚠️ Limitation: Extrapolation to humans limited.
    

💡 TOK Link The use of animals to infer human behaviour raises epistemological questions:Can knowledge derived from non-human species truly represent human cognition? What are the ethical boundaries of scientific pursuit? TOK reflection: To what extent should the pursuit of knowledge override moral constraints?

🌍 Real-World Connections Animal research contributes to understanding neurodegenerative diseases, drug addiction, and stress disorders. Ethical frameworks like the APA Animal Welfare Guidelines (2012) guide humane treatment. Findings support treatments for PTSD, Alzheimer’s, and depression.

❤️ CAS Links Organize awareness campaigns on ethical research and animal welfare. Volunteer with shelters or NGOs to understand animal cognition and empathy. Create educational materials promoting ethical science and compassion.

🧪 IA Guidance Avoid direct animal use; simulate results with existing data or virtual tools. Use past datasets on animal behaviour or neuroscience. Discuss ethics: how your IA upholds Replacement, Reduction, and Refinement.

🧠 Examiner Tips Use precise terminology: neuroplasticity, extrapolation, 3Rs, lesion studies. Always link the study’s animal findings to human behaviour. Balance discussion of scientific contribution and ethical limitations. Evaluation marks depend on your ability to address both validity and ethics.

4.4 WATER POLLUTION

📌 Definitions Table

Term	Definition
Benthic	Refers to organisms or habitats located on or near the bottom of a water body, such as a lake, river, or ocean.
Ballast Water	Water carried in ships’ tanks to improve stability, often containing invasive species that can be released into new ecosystems.
Outcompeting	When one species displaces another by being more efficient in resource use, often leading to a decline in the less competitive species.
Hypoxia	A condition in water where oxygen levels are critically low, often due to excessive decomposition of organic matter.
Algal Bloom	Rapid increase in algae population in aquatic systems, usually caused by nutrient enrichment (eutrophication).
Biofilters	Systems using natural materials or organisms to remove pollutants from water through biological processes.
Cover Crops	Plants grown to cover the soil between main crops, reducing runoff, preventing erosion, and improving water retention.
Bioremediation	The use of microorganisms or plants to clean up polluted water or soils by breaking down contaminants.

• 🧠 Exam Tips:
  
  For terms like hypoxia and algal bloom, always mention nutrients and oxygen levels.
  
  Use cause-effect phrasing for process terms (e.g., “nutrient input → algal bloom → hypoxia”).

📌 Sources of Water Pollution

• Water pollution has multiple sources and has major impacts on marine and freshwater systems
• Types of aquatic pollutants include:
  • Organic material
  • Inorganic nutrients (nitrates and phosphates)
  • Industrial effluent
  • Urban run-off
  • Solid waste disposal
  • Toxic metals
  • Synthetic compounds
  • Suspended solids
  • Hot water
  • Oil
  • Radioactive pollution
  • Pathogens
  • Light
  • Noise
  • Invasive species

Water Pollution Effects

Pollutant	Description	Effect
Organic material	Excessive organic matter from untreated human sewage, animal waste, or decaying plant material	Leads to oxygen depletion, harmful algal blooms and eutrophication in water bodies
Inorganic nutrients	Excess nitrates and phosphates from agricultural run-off, sewage and fertilisers	Causes nutrient enrichment, leading to algal overgrowth and water quality degradation
Industrial effluent	Wastewater discharged by industrial facilities after being used in productionprocesses, containing a variety of pollutants e.g. heavy metals, toxic chemicals, organic matter and pathogens	Can be toxic to aquatic life, disrupt ecosystems, and contaminate drinking water sources
Urban run-off	Rainwater or melted snow that flows over impervious surfaces, such as roads, pavement and rooftops, picking up pollutants along the way e.g. oil, grease, pesticides, fertilisers, pet waste and litter	Degrades water quality, harming aquatic life, promoting algae blooms, and contaminating drinking water sources
Solid waste disposal	Rain falling on landfills leaches contaminants into soil and groundwater, whilst litter can end up in waterways, entangling wildlife and releasing harmful chemicals into the water	Contaminates groundwater sources and harms aquatic life
Heavy metals	Heavy metals such as mercury, lead and arsenic from industrial activities, mining, or improper waste disposal	Metals accumulate in aquatic organisms, leading to toxic effects and posing risks to human health
Synthetic compounds	Human-made chemicals, including pesticides, herbicides, pharmaceuticals and industrial pollutants	Enter water bodies through run-off, discharges, or improper disposal, potentially harming aquatic life and human health
Suspended solids	Solid particles in water, typically sediment, silt, or fine particles from erosion, construction, or dredging activities	High concentrations can impair water clarity, clog fish gills, smother benthichabitats and impact aquatic organisms such as invertebrates and their larvae
Hot water	Release of heated water into aquatic systems, often associated with industrial processes or power generation	Disrupts aquatic ecosystems, reduces oxygen levels and negatively impacts fish and other organisms (e.g. disrupting migration patterns or natural breeding cycles)
Oil	Oil spills, leaks, or discharges from shipping, oil exploration, or industrial activities	Oil coats the water surface, affecting marine and freshwater ecosystems, harming aquatic life such as seabirds and leading to long-term environmental damage
Radioactive pollution	Release of radioactive substances, often associated with nuclear accidents, mining, or waste disposal	Severe ecological and human health impacts, with prolonged exposurepotentially leading to genetic mutations and cancer
Pathogens	Presence of disease-causing microorganisms, including bacteria, viruses and parasites, often originating from sewageor animal waste	Contaminate water sources, leading to waterborne diseases (e.g. cholera) and posing risks to human and animal health
Light	Excessive artificial lighting, particularly in coastal areas	Disrupts natural light cycles, affecting nocturnal marine species and disrupting reproduction, navigation and feeding patterns of marine organisms
Noise	Noise from human activities such as shipping, sonar, construction, or offshore energy production	Disrupts communication, feeding and migration patterns of marine species (e.g. whales), leading to ecological disturbances
Invasive species	Introduction of non-native species into aquatic ecosystems, often through ballast water or occasionally intentional release (e.g. for biological control or recreational fishing purposes)	Outcompete native species, alter habitat structure, disrupt food webs and cause severe ecological imbalances (e.g. the invasion of lionfish into U.S. Atlantic coastal waters)

📌 Plastic Pollution

• Plastic pollution refers to the accumulation of plastic products in the environment, negatively affecting wildlife, habitat and humans
  • Plastic debris is a significant issue in marine environments, where it accumulates and causes various problems

Harm from oceanic plastic pollution

Wildlife impacts

• Ingestion:
  • Many marine animals mistake plastic debris for food
  • This can lead to starvation, malnutrition and death
    • For example, sea turtles often mistake plastic bags for jellyfish, leading to ingestion, which can eventually be fatal
    • Birds, such as albatrosses, have been found with stomachs full of plastic, leading to starvation
• Entanglement:
  • Animals become entangled in plastic waste like fishing nets, six-pack rings for drinks cans and plastic bags, causing injury or death
    • For example, seals often get caught in discarded fishing gear, leading to severe injuries or drowning
    • Whales are often found with fishing nets wrapped around their bodies, restricting movement and causing distress

• Invasive species:
  • Plastics can transport invasive species to new areas, disrupting local ecosystems
    • Barnacles and other small crustaceans can hitch rides on floating plastic debris, spreading to new regions and potentially outcompeting local species
• Chemical leaching:
  • Plastics can release toxic additives into the water, such as bisphenol A (BPA)
    • BPA, used in manufacturing plastics, can leach into water and has been shown to interfere with the reproductive systems of some aquatic species

Human and economic impacts

• Water quality:
  • Plastic pollution can degrade water quality, affecting human populations that rely on these water sources
• Tourism industry:
  • Polluted beaches and coastal areas can deter tourists, affecting local businesses and economies
    • For example, beaches littered with plastic waste can lead to a decline in tourism, impacting local hotels, restaurants and other businesses
• Recreational activities:
  • Plastic pollution can interfere with recreational activities such as swimming, diving and boating

Aggregation in oceanic gyres

• Plastics are carried by rivers and streams into the ocean
• Ocean currents transport these plastics, which then become trapped in the rotating currents of gyres
  • Gyres are large systems of circular ocean currents
  • They are formed by global wind patterns and forces created by the Earth’s rotation
• This leads to plastic accumulating in these gyres over time, forming large patches of debris
  • For example, the Great Pacific Garbage Patch is a well-known gyre, containing an estimated 1.8 trillion pieces of plastic

Microplastics and the food chain

• Microplastics are small plastic particles less than 5mm in diameter
• They come from larger plastic debris breaking down or from products like cosmetics and clothing

• Food chain entry:
  • Microplastics are ingested by small marine organisms
  • These organisms are then eaten by larger predators in higher trophic levels
  • This leads to bioaccumulation and biomagnification
    • This is where concentrations of microplastics and their associated toxins increase up the food chain
  • This can eventually lead to microplastics in human food sources
    • For example, studies have found microplastics in fish and shellfish sold for human consumption, indicating a direct pathway to humans
• Transport of toxins
  • Plastics can absorb harmful chemicals from the environment
  • When ingested by marine life, these toxins can enter the food chain, posing health risks to animalsand humans
    • For example, chemicals like polychlorinated biphenyls (PCBs) and pesticides found on microplastics have been linked to cancer, reproductive issues and disruption of hormonal systems in animals and humans

Management and solutions

• Management is needed to remove plastics from the supply chain and to clear up existing pollution
  • Some management strategies include:

1. Reduction strategies:
   • Implementing policies to reduce plastic production and usage
   • Promoting alternatives to plastic, such as biodegradable materials
     • For example, the UK has introduced a ban(opens in a new tab) on single-use plastic straws, drinks stirrers and cutlery
2. Cleanup efforts:
   • Organising beach cleanups and developing technologies for ocean cleanups to remove existing plastic pollution
     • For example, the Ocean Cleanup(opens in a new tab) project aims to remove large quantities of plastic from the Great Pacific Garbage Patch and other water bodies using advanced technology
3. Recycling and waste management:
   • Improving recycling rates and waste management systems to prevent plastic from entering the ocean
   • Encouraging the public to recycle and dispose of waste responsibly

📌 Monitoring and Assessing Water Quality

Monitoring & assessing water quality

• Water quality is the measurement of chemical, physical and biological characteristics of water
  • Chemical characteristics include: levels of dissolved substances like minerals, pollutants and nutrients
  • Physical characteristics include water clarity, temperature and turbidity (cloudiness)
  • Biological characteristics include the presence of microorganisms (e.g. bacteria) and invasive species
• Water quality is highly variable and is often measured using a water quality index (WQI)
  • Scientists use various tests to measure different water quality parameters
  • A water quality index is then calculated
  • This combines multiple measurements into a single value or score
  • This provides an assessment of the overall water quality of a particular water body
  • This index helps in easily communicating the quality of the water body to the public and policymakers
    • E.g. indicating whether water quality is good, acceptable, or poor for various uses such as drinking, recreation and aquatic organisms
  • A high WQI indicates good water quality

Water quality parameters

• Some of the different water quality parameters that can be used are:

1. Dissolved oxygen (DO)
   • Measures the amount of oxygen dissolved in water
   • Sufficient oxygen levels are important for the survival of aquatic organisms
   • Low dissolved oxygen can lead to hypoxia
     • This can suffocate or kill aquatic life
2. pH
   • Measures the acidity or alkalinity of water
   • pH impacts the survival, growth and reproduction of aquatic organisms
   • Unusual pH levels can indicate pollution, acidification, or other environmental changes
3. Temperature
   • Measures the degree of heat or coldness of water
   • Temperature affects the metabolic rates, behaviour and distribution of aquatic organisms
   • Abnormal temperature fluctuations can stress or kill aquatic life
4. Nitrates and phosphates
   • Measuring nitrates and phosphates assesses nutrient pollution in water
   • High nutrient levels can lead to eutrophication
   • Monitoring nutrient concentrations helps manage nutrient inputs and prevent water quality degradation
5. Metals
   • Testing for metals, such as mercury, lead, cadmium, or arsenic assesses contamination levels
   • Metals can accumulate in aquatic organisms
     • This poses risks to their health and the health of organisms in higher trophic levels
   • Monitoring metal concentrations helps identify pollution sources and evaluate potential ecological impacts
6. Total suspended solids (TSS)
   • TSS is the concentration of solid particles suspended in water
   • High levels of TSS can decrease water quality by blocking sunlight
     • This reduces photosynthesis in aquatic plants and disrupts aquatic food chains
   • Suspended solids can also smother the gills or breathing apparatus of aquatic invertebrates and fish
   • High TSS can be a sign of erosion, wastewater discharge, or runoff from urban and agricultural areas, leading to habitat degradation
7. Turbidity
   • Turbidity measures the clarity or cloudiness of water
     • This is affected by suspended particles
   • High turbidity can reduce light penetration
     • This reduces photosynthesis in aquatic plants and visibility for predators and prey
   • High turbidity can indicate soil erosion or urban, agricultural or industrial run-off

❤️ CAS Tip: Participate in a water quality testing project in local rivers or lakes.

Measuring key abiotic factors in aquatic systems

Abiotic factor	How abiotic factor is measured
Dissolved oxygen (DO)	Measured using an oxygen meter equipped with a probe
pH	pH levels are determined using a pH meter equipped with a probe
Temperature	Water temperature is assessed using a digital thermometer or a temperature probe
Nitrate and phosphate concentrations	Measured using  test kits, specific to each nutrientThese kits use colorimetric tests where the water sample reacts with chemicals, producing a colour change corresponding to the concentration level of the nutrient
Total suspended solids (TSS)	Measured by filtering a known volume of water through a pre-weighed filter paper, then drying and weighing the paper againThe difference in weight represents the mass of TSS collectedThis can then be converted to a concentration
Turbidity	Measured using a Secchi disc—a black and white disc lowered into the waterThe depth at which the disc disappears from sight is recordedThis indicates light penetration and turbidity in the water column

• These parameters provide valuable information about the health and condition of aquatic ecosystems
• It is crucial to compare readings from various locations, such as upstream and downstream of a sewage outlet or factory, to assess any potential impacts on the ecosystem
• Monitoring and analysing these parameters at regular intervals helps scientists, environmental agencies and policymakers to:
  • Understand the overall water quality
  • Identify potential issues
  • Implement appropriate management strategies to protect and restore aquatic ecosystems

Biochemical oxygen demand

• Biochemical oxygen demand (BOD) is a measure of the amount of dissolved oxygen required to break down the organic material in a given volume of water through aerobic biological activity
• Aerobic organisms rely on oxygen for respiration
• When there is a higher abundance of organisms or an increased rate of respiration, more oxygen is consumed
• This means that the biochemical oxygen demand (BOD) is influenced by:
  • The quantity of aerobic organisms present in the water
  • The rate at which these organisms respire
• BOD can be used as an indirect measure to evaluate:
  • The amount of organic matter within a sample
  • The pollution levels in water
    • The introduction of organic pollutants, such as sewage, leads to an increase in the population of organisms that feed on and break down the pollutants
    • This, in turn, results in increased BOD values
    • Certain species, such as bloodworms and Tubifex worms, show tolerance to organic pollution and the associated low oxygen levels
    • On the other hand, mayfly nymphs and stonefly larvae are typically only found in clean-water environments

Example of how BOD is used to indirectly measure the amount of organic matter within a sample

• Higher BOD values indicate a larger amount of organic matter present in the water sample
  • This is because more oxygen is needed for its decomposition
• By measuring the decrease in dissolved oxygen levels over a specific incubation period, BOD provides an estimate of the organic load or pollution level in the water
• BOD values are typically expressed in milligrams of oxygen consumed per litre of water (mg/L) or as a percentage of the initial dissolved oxygen level
• The BOD test involves:
  • Collecting a water sample in a closed container
  • Measuring the initial dissolved oxygen concentration
  • Re-measuring the dissolved oxygen concentration after a specific incubation period (usually 5 days) at a constant temperature (usually 20℃)
• For example:
  • A water sample has an initial dissolved oxygen concentration of 8 mg/L
  • After 5 days, the dissolved oxygen concentration decreases to 2 mg/L
  • The BOD value would be calculated as 8 mg/L – 2 mg/L = 6 mg/L
    • As the dissolved oxygen levels have decreased substantially, this indicates that the sample has a relatively high organic load

📌 Eutrophication

• Eutrophication occurs when water bodies like lakes, estuaries and coastal areas receive large amounts of mineral nutrients, mainly nitrates and phosphates
  • This often results in the excessive growth of phytoplankton, a type of microscopic algae, as well as aquatic plants
• Main nutrients involved:
  • Nitrates: often from agricultural run-off
  • Phosphates: commonly found in detergents and sewage that is discharged into waterways without proper treatment

The process of eutrophication

1. Nutrient enrichment:
   • Excess nitrates and phosphates enter the water
   • This encourages rapid growth of phytoplankton, algae and aquatic plants
2. Excessive aquatic plant growth:
   • Nutrient availability causes fast growth of aquatic plants (macrophytes) e.g. duckweed and water hyacinth
   • Dense plant growth nearer the surface can block sunlight reaching underwater plants
3. Algal bloom formation:
   • Algae also use available nutrients to grow quickly
   • For example, when the mineral ions from excess fertilisers leach from farmland into waterways, they cause rapid growth of algae at the surface of the water
   • This is known as an algal bloom
   • Eventually, algae can completely cover the water surface
4. Blocking of sunlight:
   • The algal bloom can completely block out sunlight and stop it from penetrating below the water surface
   • Aquatic plants below the water surface start to die as they can no longer photosynthesise
     • As this photosynthesis normally helps to oxygenate the water, dissolved oxygen levels begin to decrease
   • The algae also start to die when competition for nutrients becomes too intense Phytoplankton and excess aquatic plants die off
5. Decay of phytoplankton and plants leading to oxygen depletion:
   • Bacteria decompose the dead plants and algae
   • As the bacteria respire aerobically, they use up the dissolved oxygen in the water
   • The amount of dissolved oxygen in the water rapidly decreases, so aquatic organisms such as fish and insects may be unable to survive
   • Dead zones in both oceans and freshwater can occur when there is not enough oxygen to support aquatic life
   • Hypoxia = low oxygen levels in water
   • Anoxia = severe or complete depletion of oxygen in water
6. Impact on aquatic life:
   • Fish and other aquatic life die in large numbers due to lack of oxygen
   • This can eventually lead to a loss of species and imbalances in aquatic ecosystems

Image source: savemyexams.com

• Positive feedback amplifies changes, creating a reinforcing cycle in eutrophication:

1. Increased nutrients:
   • Excess nitrates and phosphates from run-off or sewage
   • Promotes rapid growth of algae and aquatic plants
2. Increased death:
   • Algae and plants die off in large numbers
   • Adds organic matter to the water
3. Increased decomposition:
   • Bacteria decompose dead organisms, consuming oxygen
   • This decomposition releases more nutrients back into the water
4. Cycle repeats:
   • Released nutrients promote further algal and plant growth
   • Each step reinforces the next, worsening eutrophication and its impacts on the aquatic ecosystem

Impacts of eutrophication

• Eutrophication can greatly affect various ecosystem services:
• Fisheries:
  • Fish kills: sudden losses of fish due to low oxygen
  • Reduced fish stocks: long-term depletion of fish populations in certain areas
• Recreation and aesthetics:
  • Unpleasant odours: decaying algae and plants release unpleasant smells
  • Water quality: poor water conditions make swimming and boating unpleasant
  • Visual pollution: algal blooms create green or murky water
  • Foam and slime: algal blooms and decaying algae can cause foam and slimy water surfaces
• Health:
  • Toxins: some algal blooms produce harmful toxins
  • Drinking water: eutrophication can lead to contamination of drinking water sources

📌 Water Pollution Management Strategies

• There are three types of strategies for managing the impacts of pollution (which relate to the stages of pollutant impact shown above):
  • Changing human activity
  • Regulating and reducing quantities of pollutants released at the point of emission
  • Cleaning up the pollutants and restoring the ecosystem after pollution has occurred

Image source: savemyexams.com

• Eutrophication and other types of water pollution can be addressed at three different levels of management:
  • The reduction of human activities that produce pollutants
  • The reduction of the release of pollution into the environment
  • The removal of pollutants from the environment and restoration of ecosystems

1. Reduction of human activities producing pollutants

• This level aims to prevent pollution at the source by changing human practices and products
• Alternatives to fertilisers:
  • Organic fertilisers: use compost or manure instead of synthetic fertilisers
  • Slow-release fertilisers: release nutrients gradually, reducing the amount of nitrate and phosphate leaching into water bodies
• Alternatives to detergents:
  • Phosphate-free detergents: use products without phosphates to minimise pollution
• Sustainable farming practices:
  • Crop rotation: improve soil health and fertility by alternating crops with different nutrient needs, reducing the need for chemical fertilisers
  • Buffer strips: plant vegetation along waterways to absorb excess nutrients

2. Reduction of pollution release into the environment

• This level focuses on treating pollution before it reaches natural waters
• Wastewater treatment:
  • Nutrient removal: use treatment plants that remove nitrates and phosphates from sewage
  • Advanced treatment methods: use methods like constructed wetlands and biofilters
• Regulation and monitoring:
  • Enforce pollution controls: introduce and enforce regulations on nutrient discharge from industries and farms
  • Monitoring programmes: regularly test water bodies for nutrient levels
• Agricultural practices:
  • Controlled fertiliser application: apply fertilisers at optimal times to minimise run-off (e.g. apply during the growing season and avoid periods of heavy rain)
  • Cover crops: plant cover crops to absorb excess nutrients and prevent soil erosion

3. Removal of pollutants and restoration of ecosystems

• This level involves cleaning up polluted environments and restoring natural ecosystems
• Pollutant removal:
  • Dredging: remove nutrient-rich mud and sediments from eutrophic lakes
  • Algae removal: physically remove excess algae from water bodies
• Ecosystem restoration:
  • Reintroduction of species: reintroduce native plants and fish that may have become locally extinct, to restore ecosystem balance
  • Habitat restoration: create or restore wetlands to filter nutrients naturally

Application to other types of pollution

These strategies can also be applied to manage other types of pollution:

• Plastic pollution:
  • Prevention: reduce plastic use and improve recycling
  • Treatment: implement systems to capture and remove plastics from waterways
  • Cleanup: remove plastic waste from beaches and oceans
• Chemical pollution:
  • Prevention: reduce the use of harmful chemicals in agriculture and industry
  • Treatment: use filtration and treatment systems to remove chemicals from wastewater
  • Cleanup: clean contaminated soils and sediments e.g. using bioremediation

🌐 EE Tip: Explore water pollution trends in a nearby watershed using chemical, biological, or policy-based approaches.

4.3 AQUATIC FOOD PRODUCTION SYSTEMS

📌 Definitions Table

Term	Definition
Autotrophic	Describes organisms that produce their own food from inorganic substances using energy from light or chemicals.
Prokaryotic	Organisms, like bacteria, that lack a membrane-bound nucleus and organelles.
Sediment Pollution	Water pollution caused by excessive soil or mineral particles entering water bodies, reducing water quality and harming aquatic life.
Ghost Nets	Abandoned or lost fishing nets that continue to trap marine organisms, causing ecological harm.
Moratorium	A temporary ban or suspension of an activity, such as commercial fishing, to allow resource recovery.
Fishing Quotas	Legally set limits on the amount or number of fish species that can be caught to promote sustainable fisheries.
Bycatch	Non-target species unintentionally caught during commercial fishing operations.
Leach	The process by which soluble substances are washed out of soil or waste into water bodies, potentially causing contamination.
Eutrophication	Nutrient enrichment of water bodies leading to excessive algal growth, oxygen depletion, and ecosystem degradation.
Biocides	Chemical substances that kill or control harmful organisms, often used in agriculture or aquaculture.
Biosecurity	Measures taken to protect ecosystems from invasive species, diseases, or biological threats.
Biorights	Ethical principle that all forms of life have the right to exist and be protected, regardless of their utility to humans.

• 🧠 Exam Tips:
  
  When defining pollution or environmental damage terms, include impact on ecosystems or biodiversity for a complete answer.
  
  Terms like bycatch, quotas, moratorium often appear in fisheries case study questions—link to sustainability when possible.

📌 Aquatic Food Webs

• Aquatic food webs show how energy and nutrients move through freshwater and marine ecosystems

Phytoplankton

• Phytoplankton are microscopic organisms found in marine and fresh water bodies that can perform photosynthesis
  • Phytoplankton are not plants
  • They include a variety of autotrophic microorganisms, such as:
    • Algae (e.g. diatoms)
    • Cyanobacteria (prokaryotic organisms that are also known as blue-green algae) 
• Role in food webs:
  • They form the base of most aquatic food webs
  • They capture solar energy and convert it into biomass through photosynthesis
  • They are consumed by primary consumers (zooplankton and small fish)
  • They contribute to oxygen production and nutrient cycling

Macrophytes

• Macrophytes are aquatic plants that are visible to the naked eye
• They can be:
  • Emergent: plants that grow above the water surface (e.g. cattails or bulrushes)
  • Submerged: plants that grow completely underwater (e.g. seagrass)
  • Floating: plants that float on the water surface (e.g. water lilies or duckweed)
• Role in food webs:
  • They provide habitat and food for various aquatic organisms
  • They capture solar energy and convert it into biomass through photosynthesis
  • They contribute to oxygen production and nutrient cycling

Energy flow in aquatic food webs

• Producers: phytoplankton and macrophytes capture energy from sunlight through photosynthesis
• Primary consumers: zooplankton, small fish and some invertebrates and birds feed on primary producers
• Secondary consumers: larger fish and birds consume primary consumers
• Tertiary consumers: top predators like sharks and birds of prey eat secondary consumers
• Decomposers: aquatic bacteria and fungi break down dead organisms, recycling nutrients back into the ecosystem

📌 Human Consumption and Increasing Demand

• Humans consume a variety of organisms (flora and fauna) from both freshwater and marine environments
• These organisms provide essential nutrients and form a significant part of many cultures’ diets
• Consumption patterns vary locally and globally
  • This reflects availability, tradition and sustainability concerns

Examples of aquatic food resources

Local and Global Examples of Aquatic Flora and Fauna Consumed by Humans

Organism	Type of organism	Type of aquatic environment	How widely consumed	Description
Watercress	Flora	Freshwater	Local	Leafy green plantPopular in the UKGrown in shallow, flowing water beds fed by natural springs or streamsUsed in salads and soups
Spirulina	Flora	Freshwater	Global	Blue-green algae (cyanobacteria)Consumed worldwideGrown in freshwater ponds and lakesHarvested by filtering the water and then drying the algaeUsed as a dietary supplement
Dulse	Flora	Marine	Local	Type of red seaweedTraditionally eaten in IrelandHand-harvested from rocks during low tide along the coastlineDried in the sun or indoorsConsumed dried or cooked
Nori	Flora	Marine	Global	Type of red seaweedPopular globally, especially in JapanFarmed in coastal waters on nets suspended from bamboo poles or floating raftsHarvested, then dried and processed into sheetsUsed in sushi and snacks
Trout	Fauna	Freshwater	Local	Freshwater fishCommonly consumed in the UKRaised in freshwater ponds or tanks with controlled water qualityHarvested by netting when they reach market size
Tilapia	Fauna	Freshwater	Global	Freshwater fishConsumed worldwideRaised in freshwater ponds or recirculating aquaculture systemsHarvested by draining the ponds or using nets
Orkney Scallops	Fauna	Marine	Local	Type of shellfishA delicacy in Scotland, UKCollected by divers from the seabed around the Orkney Islands (ensures minimal environmental impact)
Shrimp	Fauna	Marine	Global	Small crustaceanFound in oceans worldwide and consumed globallyRaised in coastal ponds or tanksHarvested by draining the ponds and collecting the shrimp with nets

Demand for aquatic food resources

• The demand for aquatic food resources has significantly increased in over the last 50–100 years
  • This is due to the combined effects of a growing human population and dietary changes
• As populations expand and economies develop, there is a higher demand for seafood products to meet nutritional needs and culinary preferences
• The main factors behind the increase in demand for aquatic food resources are:

1. Growing human population
   • The global population has rapidly increased, resulting in a larger consumer base for aquatic food resources
2. Changing dietary patterns
   • As countries undergo economic growth, there is often a shift in dietary patterns towards increased consumption of protein-rich foods, including seafood
3. Nutritional benefits of seafood
   • Seafood is recognised as a valuable source of essential nutrients, such as omega-3 fatty acids, vitamins and minerals
   • These all contribute to human health and well-being
4. Urbanisation and the rising middle class
   • Urbanisation and the emergence of a middle class in many regions have led to changes in dietary preferences
   • This has increased demand for diverse and higher-value food options, including seafood
5. Global trade and supply chains
   • Advances in transportation and the expansion of global trade networks have made it easier to import and export seafood products
   • This has increased their availability to communities
6. Aquaculture production
   • Aquaculture, the farming of aquatic organisms, has experienced significant growth to meet the rising demand for seafood

📌 Unsustainable Harvesting Practices & Overexploitation

Unsustainable harvesting practices

• The rising global demand for seafood has led to the use of unsustainable harvesting practices
  • These methods often damage marine ecosystems and lead to overexploitation of fish stocks

1. Bottom trawling:
   • This method involves dragging heavy nets along the seabed
   • Impacts:
     • Destroys habitats such as coral reefs
     • Results in significant bycatch (catching non-target species)
     • Disturbs sediment, causing sediment pollution and releasing other trapped pollutants
2. Ghost fishing:
   • This occurs when abandoned or lost fishing gear continues to catch marine life
     • E.g. ghost nets
   • Impacts:
     • Continues to catch fish and other marine animals, leading to unnecessary deaths
     • Causes entanglement of marine organisms, including endangered species
     • Contributes to marine debris and pollution
3. Use of poisons:
   • Some fishermen use poisons and toxic substances, such as cyanide, to stun or kill fish, making them easier to catch
   • Impacts:
     • Poisons kill or damage a wide range of marine life
     • Cyanide kills coral polyps and other organisms that form the coral reef structure, leading to reef degradation and overall loss of biodiversity
     • This method is highly unsustainable and illegal in many places
4. Use of explosives:
   • Some fishermen use explosives, such as dynamite, to stun or kill fish, making them easier to catch
   • Impacts:
     • Explosives destroy marine habitats and kill indiscriminately (kill non-target species)
     • Causes extensive damage to coral reefs and other important marine habitats
     • This method is also highly unsustainable and illegal in many places

Overexploitation

• Developments in fishing equipment and increased use of unsustainable fishing methods have led to declining fish stocks and damage to habitats
  • Fish stocks in the oceans are rapidly decreasing in size
  • This is mainly due to overfishing
• Overexploitation happens when fish are harvested at a rate faster than they can reproduce
  • This can eventually lead to the collapse of fisheries, where the fish population drops so low that it cannot recover

Maximum sustainable yield

• The annual yield for a natural resource (such as a forest) is the annual gain in biomass or energy,through growth
• The maximum sustainable yield (MSY) is the maximum amount of a renewable natural resource that can be harvested annually without compromising the long-term productivity of the resource
• It is the level of harvest that can be maintained indefinitely
• The concept of maximum sustainable yield applies to various resources, such as crops, fish, timber, and game animals
  • For example, in fisheries, the concept of maximum sustainable yield is used to determine the maximum amount of fish that can be harvested sustainably from a given population
  • This is calculated based on the population size, growth rate and reproduction rate
  • If the fishing rate exceeds the maximum sustainable yield, the population may decline, and the long-term productivity of the fishery may be affected
• In summary, the maximum sustainable yield is the highest possible annual catch that can be sustained over time without depleting the fish stock
• Calculating the maximum sustainable yield is important as it helps in setting appropriate limits on fishing quotas to ensure sustainable fishing practices

📌 Mitigation Strategies

• Unsustainable exploitation of aquatic systems can be mitigated at a variety of levels (international, national, local and individual)
  • This can be achieved through policy, legislation and changes in consumer behaviour
    • For example, control of net size and the introduction of fishing quotas play important roles in the conservation of fish stocks
    • Strategies like these can keep fish stocks at a sustainable level

International and national level actions

• Increasing the size of gaps in fishing nets can help in two main ways:
  • Fewer unwanted species (that are often discarded) will be caught and killed
    • This is because they can escape through larger net gaps (as long as they are smaller than the species being caught)
    • The accidental capture and killing of larger, unwanted species is still a problem
  • Juvenile fish of the fish species being caught can escape through larger net gaps
    • This means they can reach breeding age and have offspring before they are caught and killed
    • This ensures the population of the fish species being caught can be replenished
• Fishing quotas limit the number and size of particular fish species that can be caught in a given area
  • Many nations have introduced quotas to prevent overfishing of certain species
• There are several ways to enforce governmental regulations:
  • Establishing fishing quotasAgreeing zones or areas of the ocean where fishing is banned (e.g. spawning grounds) and permitted (e.g. within a country’s territorial waters)Agreeing specific times of the year when fishing is not allowed to let fish populations recover (e.g. spawning season)Regulating mesh size of nets (to allow undersized/juvenile fish to escape)Limiting the size of the fishing fleet by issuing licences and permitsInspecting the catch as a fishing boat returns to portBanning certain practices, e.g. gillnets (static nets that catch anything that swims past),Promoting sustainable practices such as trolling (different to trawling) that reduce bycatch
• Sustainable seafood choices:
  • Encouraging consumers to buy seafood that is certified as sustainable
    • For example, the Marine Stewardship Council (MSC) label indicates sustainably sourced seafood
• Food labelling:
  • Providing clear information on the origin and sustainability of seafood products to help consumers make informed choices
    • For example, the UK’s “Blue Fish” label signifies fish caught using sustainable practices
• Community initiatives:
  • Educating the public about the importance of sustainable fishing and responsible seafood consumption
  • Supporting local fishing communities that practice sustainable fishing
  • Participating in local conservation efforts
  • Involving local communities in managing and protecting their own fisheries
    • For example, in the Philippines, community-based coastal resource management has successfully increased fish stocks and biodiversity

Marine protected areas

• Marine protected areas (MPAs) are designated regions of seas and oceans where human activities are restricted or managed
  • This is to protect marine ecosystems and biodiversity
• MPAs play a crucial role in supporting aquatic food chains and maintaining sustainable yields
  • They do this by providing safe areas for marine life

Benefits of marine protected areas

Biodiversity conservation

• Habitat protection:
  • MPAs protect critical habitats like coral reefs, seagrass beds and mangroves
    • For example, the Great Barrier Reef Marine Park protects one of the most biodiverse ecosystems on the planet
• Species protection:
  • MPAs protect endangered and vulnerable species by reducing human-induced pressures such as fishing and pollution
    • For example, the Galápagos Marine Reserve protects unique species found nowhere else in the world
    • It does this by imposing fishing restrictions and carefully managing tourism

Support for aquatic food chains

• Spawning and nursery grounds:
  • MPAs provide safe areas for fish and other marine organisms to reproduce and for juveniles to grow
• Feeding grounds:
  • By protecting areas rich in food sources, MPAs ensure that marine species have access to enough food

Spillover effect

• Population growth beyond MPA boundaries:
  • Healthy and abundant populations within MPAs can migrate to nearby areas
  • This replenishes fish stocks and benefits fisheries outside the protected zones
• Genetic diversity:
  • MPAs maintain genetic diversity by protecting breeding populations
  • This contributes to the resilience of marine species
    • For example, the Chagos Marine Reserve in the Indian Ocean supports genetically diverse populations of fish and coral

Sustainable yields

• Fisheries management:
  • MPAs can help maintain sustainable fishery yields by preventing overfishing and allowing fish populations to recover
  • Sustainable fish populations lead to more stable and long-term economic benefits for fishing communities

📌 Aquaculture

What is aquaculture?

• Aquaculture, also known as fish farming or aquafarming, refers to the cultivation of aquatic organisms in controlled environments such as ponds, tanks, or ocean enclosures
• It involves the rearing, breeding, and harvesting of various species of fish, shellfish, algae and other aquatic organisms for commercial, recreational, or conservation purposes
• Aquatic flora and fauna, both freshwater and marine, are harvested by humans through various methods to meet different needs and purposes

• Aquatic organisms that are farmed include:
  • Fish
    • e.g. salmon, tilapia and catfish
  • Molluscs
    • e.g. oysters, mussels, scallops and clams
    • e.g. snails
    • e.g. octopus and squid
  • Crustaceans
    • e.g. shrimp, prawns, lobsters and crabs
  • Aquatic plants
    • E.g. seaweed and algae

The growth of aquaculture

• Aquaculture has experienced significant growth to meet the increasing global demand for seafood
  • This is driven by population growth, changing dietary preferences and rising incomes
• Aquaculture has the potential to provide a reliable and sustainable source of seafood
  • This can help to meet the protein needs of a growing population
  • At the same time, minimise the impact on wild fish stocks
• By cultivating aquatic organisms through aquaculture, the pressure on wild fish populations can be reduced
  • This allows them to recover and the ecological balance of these marine ecosystems to be restored

   1. Providing additional food resources:

• Aquaculture contributes to global food security by providing an additional source of nutritious food resources
• Cultivating fish and shellfish through aquaculture offers a consistent supply of protein-rich seafood
  • This can help address nutritional deficiencies and improve human health in many parts of the world
• The controlled environments of aquaculture systems allow for efficient production and reduced waste

   2. Supporting economic development:

• Aquaculture has emerged as a significant sector in the global economy
  • It generates employment opportunities, income and economic growth
• It provides livelihoods for millions of people, particularly in coastal and rural communities, where fishing and aquaculture activities are integral to the local economy
• Aquaculture encourages trade and investments, contributing to the overall development and prosperity of regions and whole countries

Food for future generations

• The growth of aquaculture is expected to continue in the coming years due to several factors:
  • Rising global demand for seafood: the growing population, urbanisation and changing dietary preferences drive the need for increased seafood production
  • Technological advancements: ongoing research and technological developments in aquaculture practices, breeding techniques, feed formulations and disease management are enhancing production efficiency and sustainability
  • Environmental considerations: aquaculture is evolving towards more environmentally friendly and sustainable practices, addressing concerns such as waste management and habitat impacts
  • Innovation and diversification: the development of new species for aquaculture, such as high-value fish and seaweed, opens up opportunities for market expansion
  • Policy support: governments and international organisations are promoting and investing in aquaculture development to address food security, reduce pressure on wild fish stocks and support economic growth

Aquaculture issues

• Issues caused by aquaculture include:
  • Habitat loss
  • Pollution (with feed, antifouling agents, antibiotics and other medicines added to fish pens)
  • Spread of diseases
  • Escaped species (sometimes involving genetically modified organisms)
  • Ethical Issues and biorights

Issues in Aquaculture

Issue	Description
Habitat loss	Aquaculture facilities often require the conversion of natural habitats such as wetlands, mangroves, or coastal areas into fish farmsThese habitats are cleared or modified to create suitable spaces for aquaculture operationsThis habitat loss can have negative impacts on biodiversity, ecosystem functions and the livelihood of local communities
Pollution	Excess nutrients from uneaten feed and fish waste can leach into the surrounding water bodies, leading to eutrophication, algal blooms and oxygen depletionSome feed formulations may contain additives, such as growth enhancers or colourants, that can potentially negatively impact water qualityPowerful chemicals known as antifouling agents are used to prevent the growth of marine organisms (e.g. mussels and barnacles) on aquaculture infrastructureThese biocides can leach into the surrounding water, potentially causing harm to marine lifeTo prevent and treat diseases, aquaculture operations may use antibiotics and other medicines, which can enter the surrounding waters, posing risks to aquatic organisms and contributing to antibiotic resistance
Spread of diseases	The high density of fish in aquaculture facilities facilitates the spread of diseases among farmed fishThis leads to increased disease risks and the need for disease management strategiesIf proper biosecurity measures are not in place, pathogens can also spread from aquaculture facilities to wild fish populations, impacting their health and survival
Escaped species	Escape of farmed fish from aquaculture facilities can lead to genetic interactions with wild populationsThis impacts wild species through competition, interbreeding, or transmission of genetic diseasesSome aquaculture operations involve the use of genetically modified fishThis raises concerns about potential ecological impacts and ethical considerations if these fish breed with wild populations
Ethical Issues and biorights	Aquaculture raises ethical questions regarding the treatment and welfare of farmed animals, particularly in intensive farming systemsConcerns centre around the confinement and stress experienced by farmed species, the use of antibiotics and growth enhancers, and the overall quality of life for the animals

• In addition, issues in aquaculture can often arise regarding international conservation legislation
  • Aquaculture must comply with international conservation legislation and regulations to ensure the sustainable use of resources and to protect biodiversity
  • Compliance with these regulations helps prevent the exploitation of threatened species, maintain ecological balance and ensure the long-term viability of aquaculture practices
• Balancing environmental sustainability, animal welfare and legal obligations is crucial to maintaining an equitable and socially responsible aquaculture sector

📌 Climate Change & Ocean Acidification

• Climate change refers to significant changes in global temperatures and weather patterns over time
  • Mostly driven by human activities such as burning fossil fuels, deforestation and industrial processes
  • Leads to global warming, which is an increase in Earth’s average surface temperature

What is ocean acidification?

• Ocean acidification is the ongoing decrease in the pH of Earth’s oceans
  • Caused by absorption of excess carbon dioxide (CO₂) from the atmosphere
  • When CO₂ dissolves in seawater, it forms carbonic acid, which lowers the pH

Impacts on ecosystems

Climate change effects

• Temperature rise:
  • Warmer waters can alter habitat ranges for marine species
    • For example, many fish populations are migrating to cooler waters, impacting local fishing industries
• Melting ice caps:
  • Polar ice is important for the survival of many species
    • For example, the loss of important ice habitats will affect polar bears and seals that need them for hunting, avoiding predators and raising offspring
    • Walruses are increasingly forced to rest on land, leading to overcrowding and increased mortality
  • Leads to sea level rise, threatening coastal ecosystems
    • For example, rising sea levels are threatening the coastal mangrove forests in Bangladesh, which serve as crucial habitats for many species and protect the coastline from erosion
• Hurricane damage:
  • Increased intensity and frequency of hurricanes is damaging coral reefs (e.g. in the Caribbean)
    • For example, hurricane Irma in 2017 caused widespread coral destruction, particularly affecting the coral reefs around the Florida Keys and the Virgin Islands

Ocean acidification effects

• Coral bleaching:
  • Warmer temperatures and acidification cause coral to expel the algae that live in their tissues
  • This causes the coral to turn white (known as bleaching)
  • This often leads to coral death if the stressful conditions persist
    • For example, the Great Barrier Reef is currently experiencing massive coral bleaching events
• Shellfish vulnerability:
  • Acidic waters weaken calcium carbonate shells of marine organisms like oysters, clams, and sea urchins
  • This makes them more vulnerable to predation, disease and environmental stress,
  • This can lead to population declines and disruption of marine food webs
    • For example, oyster populations in the Pacific Northwest (USA) are in decline partly due to ocean acidification
    • Oyster farms here are struggling with reduced harvests due to shell degradation

4.2 WATER ACCESS, USE AND SECURITY

📌 Definitions Table

Term	Definition (Exam-Ready, 2 Marks)
Reverse Osmosis	A water purification method that uses pressure to force water through a semipermeable membrane, removing salts and impurities.
Groundwater Recharge	The process where water from precipitation or surface sources infiltrates into the ground and refills aquifers.
Drip Irrigation	An efficient irrigation method that delivers water directly to plant roots through a network of tubes, minimizing evaporation losses.
Water Surplus	A situation where water supply exceeds demand in a particular area or time period.
Water Deficit	A condition where water demand exceeds available supply, often leading to stress on ecosystems or agriculture.
Water Scarcity	Long-term imbalance between water demand and availability, often due to overuse or drought, affecting sustainability.
Greywater	Wastewater from domestic activities like washing and bathing, which can be reused for irrigation after treatment.
Aquaponics	A sustainable farming system that combines aquaculture (fish farming) and hydroponics, using fish waste to fertilize plants.
Hydroponics	The method of growing plants in a nutrient-rich water solution without soil, often used in controlled environments.
Conservation Tillage	A farming practice that reduces soil disturbance, helping to retain moisture, reduce erosion, and improve soil health.

• 🧠 Exam Tips:
  
  Use sustainability language (e.g., conserve, efficient, reuse) for full marks on water management strategies.
  
  Pair scarcity, surplus, and deficit with examples or causes if asked for explanation or evaluation.

📌 Factors Affecting Water Availability

• Water security is having access to sufficient amounts of safe drinking water
• Water security is essential for sustainable societies
  • Without adequate water, societies cannot continue to exist
  • Human well-being and health, agriculture and industries quickly begin to deteriorate when there is a lack of water
• Many different social, cultural, economic, political and geographical factors affect the availability of freshwater
  • These factors also affect equitable access to this freshwater (i.e. how fairly this water access is distributed between societies)

Social factors

• Population growth:
  • Larger populations increase water demand
    • For example, India’s rapidly growing population is straining its water resources
• Population density:
  • Regions with higher population densities tend to experience greater pressure on water resources
  • Increased water demand for domestic, agricultural and industrial purposes can strain available supplies
• Urbanisation:
  • Cities require very large amounts of water
• Living standards:
  • Higher living standards often lead to higher water usage
    • For example, developed countries like the USA use more water per capita than developing countries

Cultural factors

• Water conservation:
  • Cultures that prioritise water conservation tend to manage their water supplies better
  • Some cultures may not prioritise water conservation, leading to wastage
    • For example, in parts of the USA, despite ongoing droughts, water usage remains high due to a lack of conservation efforts
• Consumerism:
  • High levels of consumerism often lead to increased water consumption
    • For example, in Western countries, the high demand for consumer goods results in significant water usage for manufacturing and food production
• Traditional agriculture:
  • Some traditional agricultural methods may use water inefficiently
• Cultural attitudes towards water pollution:
  • Attitudes towards pollution can affect water quality
  • In some regions, cultural indifference towards pollution has led to severe contamination of water bodies

Economic factors

• Economic development:
  • Industrial activities require significant water resources
  • Wealthier nations often have greater financial resources to invest in water infrastructure and management, which can result in better access to fresh water
  • In contrast, poorer countries may lack the means to develop and maintain robust water systems
• Investment in infrastructure:
  • The presence of well-developed water management systems, including reservoirs, dams, canals, and pipelines, can enhance water availability and distribution
  • Investing in water treatment facilities ensures a better supply of safe drinking water
• Agricultural needs:
  • Agriculture is a major water consumer
    • For example, in Egypt, a large portion of water from the Nile River is used for irrigation

Political factors

• Government policies:
  • Policies and regulations affect water distribution and quality
    • For example, South Africa’s National Water Act aims to ensure equitable water access and that the basic human needs of current and future generations are met
• International agreements:
  • Transboundary water management requires cooperation between countries
    • For example, the Nile Basin Initiative involves multiple countries working together to manage the Nile River’s resources.
• Conflict and stability:
  • Political instability and conflicts can disrupt water supplies

Geographical factors

• Geographic location:
  • Some regions naturally contain abundant freshwater resources due to factors such as proximity to large rivers, lakes, or high rainfall
  • Others, like arid and semi-arid regions, naturally have limited water availability
• Climate:
  • Areas with high levels of precipitation, such as tropical rainforests or coastal regions, generally have better access to fresh water compared to arid or desert regions with low rainfall
• Topography:
  • Mountainous regions often have better access to fresh water
  • This is due to higher precipitation rates and the presence of glaciers and snowpack that act as natural reservoirs
  • Conversely, flat or low-lying areas may face challenges in water availability

🔍 TOK Tip: Who owns water? How do power structures influence access to natural resources?

📌 Strategies for Increasing Water Supply

• Human societies undergoing population growth or economic development need to increase the supply of water or use it more efficiently
• Water is essential for:
  • Domestic use
  • Agriculture (drinking-water for livestock and irrigation-water for crops) 
  • Industry

Strategies Used to Increase Fresh Water Supplies

Strategy	Description	Example
Constructing dams and reservoirs	Structures built to store water, regulate flow and prevent floodsHelps store water during periods of high rainfall for use during dry seasons	The Hoover Dam in the USA creates Lake Mead, supplying water to several states and generating hydroelectric power
Rainwater Catchment Systems	Collecting and storing rainwater run-off from rooftops or other surfaces for domestic useCollected rainwater can be used for non-potable purposes like irrigation, toilet flushing and cleaning, reducing the strain on freshwater sources	In Chennai, India, rooftop rainwater harvesting helps tackle water scarcityIt also mitigates stormwater run-off, reducing flooding and erosion
Desalination Plants	Removing salt and minerals from seawater to produce freshwater using methods like reverse osmosis	The Jebel Ali Desalination Plant in Dubai provides a significant portion of the city’s water supply
Enhancement of Natural Wetlands	Improving wetlands to act as natural filters, removing pollutants and aiding groundwater recharge	The Everglades in Florida, USA, are being restored to enhance water flow and quality
Improving Irrigation Methods	Using efficient irrigation techniques like drip irrigation to reduce water wastage in agriculture	In Israel, the development and use of advanced drip irrigation technology has maximised water use efficiency
Water Recycling and Reuse	Treating wastewater for reuse in industrial processes or irrigation	Singapore’s NEWater project treats and reuses wastewater, reducing reliance on imported water
Artificial Recharge of Aquifers	Increasing groundwater supplies by directing surface water into the ground to replenish aquifersRecharging aquifers helps prevent groundwater depletion and maintains a sustainable supply of water for wells and springs	In California, USA, managed aquifer recharge projects help counteract over-extraction of groundwater
Redistribution	Efficient water redistribution systems, such as canals and pipelines, transfer water from water-rich regions to areas experiencing scarcityRedistributing water resources can help balance supply and demand, particularly in densely populated or arid regions	The Central Arizona Project in the USA redistributes water from the Colorado River to arid regions of Arizona

Using a combined approach

• Sustainable management of freshwater resources requires a combination of strategies to enhance water supplies
  • Dams, reservoirs, rainwater catchment systems, desalination plants and enhancement of natural wetlands are effective approaches to increase water availability
  • However, these measures can be complemented by water conservation practices, recycling and reuse, recharging of aquifers and sustainable agriculture
• By adopting a comprehensive and balanced approach, societies can ensure the sustainable use of freshwater resources

📌 Addressing Water Scarcity

• Water is unevenly distributed around the globe
• There are significant areas of water surplus and water deficit
• Around 450 million people in LICs suffer from severe water shortages
• Around 1.2 billion live in areas of water scarcity
• Physical water scarcity occurs where demand for water outstrips supply, often due to arid climate and low rainfall
• Economic water scarcity is where water is available but people can’t afford it or the infrastructure is inadequate

Domestic Water Conservation Techniques

Technique	Description
Metering	Install water metres to monitor and control water usage accuratelyIt helps households track their consumption
Rationing	Set limits on water usage per householdThis can involve implementing quotas or tariffs based on usage levels
Grey-water Recycling	Capture and treat greywater for reuse in non-potable applications like toilet flushing or outdoor irrigation
Low-flush Toilets	Install toilets with low-flow mechanisms to reduce water usage per flush
Rainwater Harvesting	Collect and store rainwater for tasks such as watering gardens or washing vehicles.

Industrial Water Conservation Techniques (Food Production Systems)

Technique	Description
Greenhouses	Use greenhouses equipped with large-scale rainwater harvesting systems to irrigate the crops grown inside)
Aquaponics Systems	Integrated aquaponics systems combine fish farming with hydroponic plant cultivationThese closed-loop systems recycle water between fish tanks and plant beds, reducing overall water consumption
Drip Irrigation	Install agricultural drip irrigation systems to deliver water directly to the roots of crop plants, minimising evaporation and surface run-off
Drought-resistant Crops	Develop and cultivate crops that are resilient to drought conditionsThese crops require less water to grow and are suited for arid regions
Switching to Vegetarian Food Production	Transition to plant-based agriculture to reduce the significant water usage associated with livestock farming

Case Study

Mitigation Strategies for Water Scarcity

Country Case Study: Australia

• Some parts of Australia face water scarcity challenges due to the arid climate and variable rainfall
• To address these issues, the country has implemented a range of innovative water management strategies, including:

1. Water pricing mechanisms
   • Tiered water pricing: Australia uses a tiered pricing structure where the cost of water increases with higher usage levels
     • This approach incentivises households and businesses to conserve water
   • Water trading: in regions like the Murray-Darling Basin, water trading allows users to buy and sell water allocations
     • This market-based approach helps allocate water more efficiently, especially during drought periods
2. Desalination plants
   • Sydney Desalination Plant: Sydney’s only major source of non-rainfall dependent drinking water
     • This plant can supply up to 15% of Sydney’s drinking water, providing a reliable water source during droughts
     • It uses reverse osmosis to remove salt and impurities from seawater, ensuring a continuous supply of fresh water
   • Perth Desalination Plant: one of the largest desalination plants in the Southern Hemisphere
     • It meets about half of Perth’s water needs
     • This demonstrates the effectiveness of desalination in supplementing traditional water sources
3. Water recycling programmes
   • Purple pipe systems: in some cities, recycled water is delivered through a separate “purple pipe” system for non-potable uses
     • This includes irrigation, industrial processes and toilet flushing
     • This reduces the demand on potable water supplies
   • Western Corridor Recycled Water Scheme: this project in Queensland treats and purifies wastewater to a standard suitable for industrial use
     • In times of need, it can also supplement drinking water supplies
4. Crop selection and rotation
   • Drought-resistant crops: farmers are encouraged to grow crops like sorghum and millet
     • These require less water and are more resilient to dry conditions
     • Research institutions, such as the Commonwealth Scientific and Industrial Research Organisation (CSIRO), are developing new varieties of drought-tolerant crops
   • Sustainable farming practices: using crop rotation and conservation tillage helps maintain soil moisture and reduce water usage
     • For example, rotating legumes with cereals can improve soil fertility and reduce the amount of irrigation required
5. Community awareness and education
   • Water conservation campaigns: public awareness campaigns, such as “Target 155” in Victoria, encourage residents to limit their water use to 155 litres per person per day
     • These campaigns educate the public on water-saving techniques and the importance of water conservation
   • School education programmes: schools incorporate water conservation into their curricula, teaching students about sustainable water use and the importance of preserving this vital resource

• These strategies illustrate Australia’s comprehensive approach to managing water scarcity through a combination of technological innovation, economic incentives and public education

4.1 WATER SYSTEMS

📌 Definitions Table

Term	Definition
Groundwater	Water stored beneath Earth’s surface in soil pore spaces and rock formations.
Aquifers	Underground layers of permeable rock or sediment that store and transmit groundwater.
Steady State	A condition in which the inputs and outputs of a system are balanced, maintaining stability over time.
Natural Surface Discharge	The release of groundwater to the surface via springs, rivers, or seepage.
Subsurface Flow	The lateral movement of water beneath the surface, often through soil layers toward streams or aquifers.
Evapotranspiration	The combined process of water evaporation from land and transpiration from plants.
Erosion	The physical removal of soil or rock by wind, water, or gravity, often accelerated by human activity.

• 🧠 Exam Tips:
  
  For hydrological terms, include movement or storage of water and specify where it occurs (surface, subsurface, underground).
  
  Use systems language (e.g., input, flow, storage) where applicable.

📌 Hydrological Cycle

• The hydrosphere includes all Earth’s water, such as oceans, rivers, lakes and atmospheric moisture
  • Fresh water only makes up a small fraction (approximately 2.5% by volume) of the Earth’s water storages
  • Of this fresh water, approximately 69% is stored in glaciers and ice sheets and 30% is stored as groundwater
  • The remaining 1% of freshwater is in rivers, lakes and the atmosphere
• All water is part of the hydrological cycle

• Gravity and solar radiation both influence the movement of water in the hydrosphere
  • The Sun’s heat causes water to evaporate from oceans, lakes, and rivers
  • Water vapour cools and condenses into clouds, releasing heat
  • Gravity pulls condensed water back to Earth via the process of precipitation (rain, snow, sleet, or hail).
  • Gravity causes water to flow over land into rivers and streams (runoff) and drain through soil
  • Rivers flow downhill due to gravity, moving water from inland back to the oceans

Components of the hydrological cycle

• The global hydrological cycle is a closed system
• Within the hydrological cycle, there are stores and flows
• The hydrological cycle is a series of processes in which water is constantly recycled through the system
  • The cycle also shapes landscapes, transports minerals and is essential to life on Earth
• The main stores occurring within the hydrological cycle are:
  • Oceans
  • Glaciers and ice caps
  • Groundwater and aquifers
  • Surface freshwater (rivers and lakes)
  • Atmosphere
• The main flows occurring within the hydrological cycle are:
  • Transformations: processes where the state or form of water changes, e.g.
    • Evaporation (the sun evaporates surface water into vapour)
    • Condensation (water vapour condenses and precipitates)
  • Transfers: movements of water from one location to another without changing state, e.g.
    • Water runs off the surface into streams and reservoirs or beneath the surface as ground flow
• These flows move the water on Earth from one store to another (river to ocean or ocean to atmosphere)

Image source: savemyexams.com

• Flows in the hydrological cycle include the following:

Flows in the Hydrological Cycle

Flow	Type	Description
Evaporation	Transformation	The process by which liquid water changes into a gaseous state (water vapour) and enters the atmosphere from water bodies such as oceans, lakes, and rivers
Transpiration	Transformation	The process by which plants absorb water from the soil through their roots and release it as water vapour through tiny openings called stomata in their leaves
Evapotranspiration	Transformation	The combined process of water vaporisation from the Earth’s surface (evaporation) and the release of water vapour by plants ( transpiration)
Sublimation	Transformation	The direct transition of water from a solid state (ice or snow) to a vapour state without melting first
Condensation	Transformation	The process by which water vapour in the atmosphere transforms into liquid water, forming clouds or dew, as a result of cooling
Melting	Transformation	The process by which solid ice or snow changes into liquid water due to an increase in temperature
Freezing	Transformation	The process by which liquid water changes into a solid state (ice or snow) due to a decrease in temperature
Advection	Transfer	The wind-blown movement of water vapour or condensed/frozen water droplets (clouds)
Precipitation	Transfer	The process of water falling from the atmosphere to the Earth’s surface in the form of rain, snow, sleet, or hail
Surface run-off	Transfer	The movement of water over the Earth’s surface typically occurs when the ground is saturated or impermeable, leading to excess water
Infiltration	Transfer	The process of water seeping into the soil from the surface, entering the soil layers and becoming groundwater
Percolation	Transfer	The downward movement of water through the soil and underlying rock layers, eventually reaches aquifers or groundwater reservoirs
Streamflow	Transfer	The movement of water in streams, rivers, or other water bodies, driven by gravity and the slope of the land, ultimately leads to oceans or lakes
Groundwater flow	Transfer	The movement of water through the pores and spaces in underground soil and rock layers, often moving towards rivers, lakes or oceans

📌 Human Impacts on the Hydrological Cycle

• Human activities have significant impacts on the hydrological cycle
  • They alter the natural processes of surface run-off and infiltration
• These activities include:
  • Agriculture (specifically irrigation)
  • Deforestation
  • Urbanisation

Impact of agriculture and irrigation

• Irrigation is the process of artificially supplying water to crops
  • It has a direct impact on the hydrological cycle by modifying the water distribution and availability in a region
• Increased irrigation leads to:
  • Artificially high evapotranspiration rates
  • This is because more water is supplied to plants than would occur naturally
  • This results in increased atmospheric moisture levels
  • This can lead to localised increases in precipitation downwind of irrigated areas, altering rainfall patterns in the region
• Excessive irrigation can also result in increased surface run-off
  • Water is applied faster than the soil can absorb it
  • This causes water to flow over the soil surface, carrying sediments, fertilisers, and pesticides
  • This leads to water pollution and nutrient imbalances

Impact of deforestation

• Deforestation refers to the clearing or removal of forests
  • This is primarily for agriculture, logging or urban development purposes
• Forests play a crucial role in the hydrological cycle
  • They act like natural sponges
  • They absorb rainfall and facilitate infiltration
    • This helps to recharge groundwater and maintain stream flows
• When forests are cleared, surface runoff increases significantly
  • Without the tree canopy and vegetation to intercept and slow down rainfall, more water reaches the ground surface
  • This leads to higher surface runoff rates
• Deforestation also reduces evapotranspiration rates
  • As trees are removed, there is less transpiration and evaporation occurring
  • This results in reduced moisture release into the atmosphere
• Overall, deforestation disrupts the balance between surface run-off and infiltration
  • This can lead to increased erosion, reduced groundwater recharge and altered stream flow patterns

Impact of urbanisation

• Urbanisation involves the transformation of natural landscapes into urban areas with buildings, roads and infrastructure
• Urban development significantly alters the hydrological cycle by:
  • Replacing permeable surfaces (such as soil and vegetation) with impermeable surfaces(concrete, asphalt)
    • Impermeable surfaces prevent infiltration
    • This leads to reduced groundwater recharge
    • Instead of infiltrating into the soil, rainfall quickly becomes surface run-off
    • This results in increased flooding and diminished water availability during dry periods
• Urban areas typically have efficient drainage systems designed to quickly remove excess water
  • This further accelerates surface run-off
  • This can overload natural water bodies and cause downstream flooding
• Urban areas often experience higher temperatures due to the urban heat island effect
  • This effect is caused by the concentration of buildings and paved surfaces
  • It can lead to increased evaporation rates
  • This can alter local precipitation patterns

Steady state of water bodies

• Understanding the steady state of a water body involves analysing the balance between inputs and outputs
  • This balance ensures that the water level remains constant over time

Flow diagrams of inputs and outputs

• Flow diagrams visually represent the water inputs and outputs for a water body
• Inputs: e.g.
  • Precipitation: rain, snow, or other forms of water falling directly into the water body
  • Surface run-off: water flowing over the land into the water body
  • Groundwater Inflow: water moving into the water body from underground sources
• Outputs: e.g.
  • Evaporation: water turning into vapour and leaving the water body
  • River outflow: water leaving the water body through rivers or streams
  • Groundwater outflow: water moving out of the water body into underground aquifers
  • Agricultural extraction: water that is extracted for irrigation

• For example, a lake that is at a steady state may have the following inputs and outputs:
  • Inputs: river inflow (80 units), rainfall (30 units), groundwater inflow (40 units), surface run-off (30 units)
  • Outputs: river outflow (80 units), evaporation (30 units), groundwater outflow (40 units), agricultural extraction (30 units)
  • Steady state: inputs (180 units) equal outputs (180 units)
• This is an example of sustainable water harvesting
  • Sustainable harvesting means taking water from a water body at a rate that does not exceed the rate of natural replenishment
  • Assessing the total inputs and outputs of a water body can help calculate sustainable rates of water harvesting
  • This ensures the harvested water amount does not disrupt the steady state

• If total outputs are greater than total inputs, then the water body will decrease in size
  • This may be due to unsustainable water harvesting for agriculture or for domestic and industrial purposes, e.g. water used in drinking, cleaning, heating and cooling systems, and manufacturing processes
  • Water may be extracted faster than it can be naturally replenished
• For example, an aquifer that is being unsustainably harvested (and therefore is not at a steady state) may have the following inputs and outputs:
  • Inputs: precipitation (70 units), surface infiltration (80 units)
  • Outputs: natural surface discharge (30 units), subsurface flow (70 units), groundwater extraction for domestic and industrial use (150 units)
  • Steady state disruption: inputs (150 units) are less than outputs (250 units), causing a water deficit of 100 units
• This is why groundwater extraction must be balanced with recharge rates—to prevent aquifer depletion

📘 Notes

Overview
Evolutionary psychology explains behaviour as adaptive responses shaped by natural selection to enhance survival and reproduction. Behaviours are viewed as evolved mechanisms encoded genetically.

Key Concepts

• Adaptation: Traits that increase survival likelihood.
  
• Natural Selection: Differential survival of advantageous traits.
  
• Sexual Selection: Traits that increase reproductive success.
  

Key Study 1: Buss (1989)

• Aim: Investigate cross-cultural preferences in mate selection.
  
• Method: 10,000 participants across 37 cultures completed questionnaires.
  
• Findings: Women preferred financial stability; men preferred youth and physical attractiveness.
  
• Conclusion: Universal patterns reflect evolutionary pressures.
  
• Evaluation:
  
  • 👍 Large cross-cultural data.
    
  • 👎 Social desirability bias; gender role stereotypes.
    

Key Study 2: Curtis et al. (2004)

• Aim: Explore whether disgust evolved as a disease-avoidance mechanism.
  
• Findings: Stronger disgust response to disease-related images.
  
• Conclusion: Disgust has adaptive, evolutionary roots.
  
• Evaluation:
  👎Online survey limits control; 

👍large sample strengthens reliability.

💡 TOK Links To what extent is evolutionary psychology speculative rather than empirical? How do values and cultural assumptions shape scientific explanations of human nature?

🌍 Real-World Connections Explains modern stress, phobias, mate selection patterns, and parental investment.

❤️ CAS Links Debate or podcast: “Are human behaviours products of evolution or culture?”

🧪 IA Guidance Experimental replications of disgust-response studies (Curtis-style) possible within ethics.

🧠 Examiner Tips Always connect evolutionary theory to specific behaviours (e.g., disgust, attraction). Avoid teleological (goal-driven) language — natural selection has no intent.

📘 Notes

Overview
Twin and family studies are classic tools to separate genetic from environmental influences. Monozygotic (MZ) twins share ~100% of their DNA, while dizygotic (DZ) share ~50%, allowing comparison of heritability estimates.

Key Study 1: Kendler et al. (2006)

• Aim: Investigate heritability of major depression.
  
• Method: Over 42,000 Swedish twins studied via registry data.
  
• Findings: Heritability of depression ≈ 38%; higher in women.
  
• Conclusion: Genetic factors moderately contribute to depression, but environment remains key.
  
• Evaluation:
  
  • 👍 Large, representative sample.
    
  • 👎 Correlational; cannot pinpoint causal genes.
    

Key Study 2: McGuffin et al. (1996)

• Aim: Examine concordance rates for depression.
  
• Findings: MZ = 46%; DZ = 20%.
  
• Conclusion: Genetic factors strongly implicated; environment still important.
  

Key Study 3: Scarr & Weinberg (1983)

• Adoption study on intelligence: adopted children resembled biological parents more in IQ → genetic influence significant.
  

💡 TOK Links How do probabilistic correlations challenge what it means to “know” something scientifically?Can statistical data truly explain human individuality?

🌍 Real-World Connections Twin registries used in studying addiction, personality, and schizophrenia.Policy implications for early screening and interventions.

❤️ CAS Links Create informative posters explaining twin research ethics.

🧪 IA Guidance Model twin correlations through small class surveys comparing siblings’ traits.

🧠 Examiner Tips Always explain why twin studies are used (control for genes).Avoid stating “genes cause behaviour” — always refer to interaction.

📘 Notes

Overview
Genetic inheritance refers to the transmission of biological traits from parents to offspring through genes. In psychology, it explores how inherited genetic information influences behaviour, personality, intelligence, and susceptibility to mental disorders.

Key Terms

Term	Definition
Genotype	The genetic makeup of an individual.
Phenotype	Observable characteristics resulting from genotype-environment interaction.
Heritability	The proportion of observed variation in a trait that can be attributed to genetic factors.
Gene expression	The process by which information from a gene is used to synthesize functional products like proteins, influenced by environment.
Epigenetics	Study of how environmental factors affect gene expression without altering DNA sequence.

Genetic Influence on Behaviour
Genes affect brain structure, neurotransmitter systems, and hormone regulation — which, in turn, influence cognition, emotion, and behaviour. However, behaviour is polygenic and shaped by complex gene–environment interactions (GxE).

Key Study 1: Bouchard and McGue (1981)
Meta-analysis of intelligence studies among twins and families.

• Aim: To investigate the heritability of intelligence.
  
• Method: Reviewed 111 twin studies comparing IQ correlations in MZ (identical) and DZ (fraternal) twins reared together/apart.
  
• Findings: MZ twins reared together = 0.86 IQ correlation; MZ apart = 0.72; DZ together = 0.60.
  
• Conclusion: Intelligence has a significant genetic component (~70%), but environment still plays a role.
  
• Evaluation:
  
  • 👍 Large sample increases reliability.
    
  • 👎 Publication bias possible; “intelligence” operationalization varies.
    
  • 👎 Correlational; cannot infer causation.
    

Key Study 2: Caspi et al. (2003)
Gene–environment interaction and depression.

• Aim: To test the influence of the 5-HTT gene (serotonin transporter) on depression.
  
• Method: Longitudinal study; 847 New Zealand adults genotyped for short (s) and long (l) alleles.
  
• Findings: Those with two short alleles had more depressive symptoms following stressful events.
  
• Conclusion: Genetic vulnerability interacts with environmental stress → supports diathesis–stress model.
  
• Evaluation:
  
  • 👍 Real-world applicability to mental health risk.
    
  • 👎 Self-report bias; correlational; ethics in genetic disclosure.
    

💡 TOK Links To what extent does knowing your genetic predisposition shape personal identity and free will? How do probabilistic claims in genetics challenge what we consider “knowledge” in human sciences?

🌍 Real-World Connections Gene therapy and CRISPR raise ethical debates about manipulating genetic traits. Personalized medicine uses genetic testing to tailor antidepressant or cancer treatments.

❤️ CAS Links Create an awareness campaign or discussion on genetic testing and ethical implications in schools.

🧪 IA Guidance IAs can explore heritability through simulated twin studies or survey-based measures of personality and environment.

🧠 Examiner Tips Always define heritability clearly (percentage variance explained by genes). Distinguish between genetic determinism and interactionist approaches.