Author: Admin

📌What is the circular flow of income?

A model that illustrates how income and output circulate between different sectors of the economy, showing the continuous movement of money, resources, and goods/services. Money earned by households flows to firms when they spend it on goods and services, and flows back as income when firms pay for labor and resources. So, what do you think happens if households stop spending and start saving all their income? To answer this you need to understand the circular flow of income!

📌How the circular flow of income works:

1. Households provide factors of production (land, labor, capital, entrepreneurship) to firms.
2. Firms pay households income (wages, rent, interest, profit).
3. Households use this income to purchase goods and services from firms
4. This creates a cycle of economic activity.

For example a small town has a café called Brew & Bite, and it interacts with households, the government, banks, and international trade. Sarah, a local resident, works as a barista at Brew & Bite who pays a wage for her labour. This is income to the household. Sarah uses part of her wage to buy coffee and snacks at Brew & Bite which is spending (consumption). This shows how money flows from the firm to the household and then back to the firm.

Additionally, Brew & Bite earns revenue from customers like Sarah. It uses this money pay wages to staff, buy coffee beans and pastries from suppliers and pay rent and electricity bills. This shows how firms use income to pay for factors of production.

📌Additional flows:

Leakages

Leakages are withdrawals of money from the circular flow of income, reducing the total amount of spending in the economy.

Savings: Money that households or businesses choose not to spend on goods and services, instead putting it into banks or other financial institutions. Moving back to the previous example if Sarah saves part of her salary in a bank account. It would be a leakage because it is withheld from the circular flow, meaning it’s not going to businesses so the flow of money between households and firms slows down, which can reduce income, production, and employment.

Imports: Spending on foreign-produced goods and services. Money leaves the domestic economy to pay for these goods. Going back to my previous example, Brew & Bite imports specialty coffee beans from Colombia. This is a leakage because money leaves the local economy.

Taxes: Money collected by the government from individuals and businesses in the form of income tax, corporate tax, VAT, etc. For example, if Brew & Bite pays business taxes to the government then that would be a leakage.

Injections

Injections are additions of money into the circular flow, increasing the total level of spending in the economy.

Investment: Spending by businesses on capital goods like machinery, buildings, and technology. Brew & Bite also takes a loan from the bank to renovate the shop. This is an example of investment because the café is spending money on capital improvements that will increase its production capacity and improve efficiency. This spending creates new income for construction workers, suppliers, and equipment providers, keeping money moving through the economy. Thus, it is an injection into the circular flow of income because it adds new spending beyond just consumption.

Government spending: Expenditures by the government on goods and services such as infrastructure, healthcare, and education. For example, the government using tax revenue to subsidize local businesses and build better roads near Brew & Bites will be an injection because these government actions create income for construction workers, suppliers, and other firms involved in the projects, further circulating money through the economy.

Exports: Goods and services produced domestically and sold to foreign consumers. This brings money into the domestic economy. Brew & Bite also sells locally made coffee mugs online to customers abroad. This is an injection because foreign customers pay in foreign currency, which gets converted to local income, bringing new money into the domestic economy.

📌 Assumptions of the circular flow of income:

• Only Two Sectors: households and firms (no government or foreign trade). Households provide factors of production (land, labour, capital, enterprise), and firms produce goods and services and pay households factor incomes (wages, rent, interest, profit). For example, the foreign sector which includes exports and imports is not included. In the real world, economies have governments (taxation, spending, regulations) and foreign sectors (exports/imports). Modern economies are interdependent, involving trade, financial markets, public services, and more. People these days don’t just work and spend. They save, invest and pay taxes which this model excludes. Have you made any recent investments lately in crypto or elsewhere?
• No Government Intervention: no taxes or government spending and no public sector influence on the economy. However in the real world governments play a crucial role. They regulate industries and provide public goods. For example, in the early 2000s, the U.S. financial sector operated with minimal government oversight. Banks and mortgage lenders engaged in high-risk lending, giving loans to people who couldn’t afford them (subprime mortgages). The government failed to regulate these risky financial instruments (like mortgage-backed securities and derivatives). There were no checks on how much risk banks could take, and financial markets became overleveraged. Ratings agencies also went unregulated, giving AAA ratings to risky assets. As a result, when homeowners defaulted on their loans, the financial system began to collapse. Major banks and firms (like Lehman Brothers) failed, and a global credit crisis followed. Thus, During the 2008 financial crisis, the U.S. government and Federal Reserve intervened with bailouts for major banks, AIG, and auto companies, emergency interest rate cuts, stimulus packages to revive the economy, and introduced the Dodd-Frank Act (2010) to increase financial sector oversight and prevent future crises. Without government intervention, there’s no way to address market failures like poverty, pollution, or monopolies.
• No Foreign Sector: no imports or exports, and all goods and services are produced and consumed domestically. Whereas in reality, countries rely on trade for resources they don’t have (e.g., oil, tech, food). For example, India imports oil from Russia for most of the transportation system to work.
• All Incomes Are Spent (No Savings): households spend all their income on consumption. In reality, households save a portion of their income for retirement, education, and emergencies or future purchases. Did you know Indian households are among the largest savers of gold in the world? Indian families hold an estimated over 25,000 tonnes of gold, more than the reserves of most central banks. Rather than spending all income on goods and services, many Indian households convert a portion of their earnings into physical gold, treating it as a form of savings or investment. Thus, not all income is spent.

📌 Can you guess the equilibrium condition?

It is when total leakages = total injections.

📌 Advantages of Equilibrium in the Circular Flow of Income

📌Disadvantages of disequilibrium in the Circular Flow of Income

🔍 TOK Perspective: “To what extent can economic models like the circular flow accurately reflect real-world complexity?” This model is a simplification which helps us understand the economy however human behaviour is not always rational or predictable, and the model assumes constant flows (no delays, uncertainty). Additionally, it doesn’t show inequality or informal sectors.

📌Definition Table

Term	Definition
In-situ Conservation	Protecting species in their natural habitat.
Ex-situ Conservation	Conserving species outside their natural habitat, such as in zoos or botanical gardens.
Protected Area	A designated region managed to conserve biodiversity and natural resources.
Restoration Ecology	The process of assisting the recovery of degraded ecosystems.
Sustainable Use	Using biological resources in a way that does not lead to long-term decline.

📌Introduction

Conservation strategies aim to protect biodiversity, maintain ecosystem services, and ensure the sustainable use of natural resources. These strategies operate at global, national, and local levels, and include both proactive measures to prevent biodiversity loss and reactive measures to restore degraded ecosystems. Effective conservation requires a combination of in-situ and ex-situ methods, legal protection, community involvement, and integration with sustainable development goals.

📌 In-situ Conservation Strategies

• Establishment of national parks, wildlife reserves, and marine protected areas.
• Legal enforcement against poaching, logging, and illegal fishing.
• Habitat restoration to support natural populations.
• Community-based conservation projects involving local stakeholders.
• Ecological corridors to connect fragmented habitats.
• Control of invasive species within protected areas.

🧠 Examiner Tip: Always highlight that in-situ conservation maintains natural ecological processes and species interactions.

📌 Ex-situ Conservation Strategies

• Zoos and aquaria for captive breeding and reintroduction programmes.
• Botanical gardens and seed banks preserving plant genetic diversity.
• Cryopreservation of gametes and embryos for rare species.
• Gene banks for agricultural crops and livestock.
• Rescue and rehabilitation centres for injured wildlife.
• Ensures survival when in-situ conservation is not possible.

🧬 IA Tips & Guidance: An IA could assess germination rates of seeds stored under different conditions to model seed bank viability.

📌 Legal and Policy Measures

• National biodiversity strategies aligned with the Convention on Biological Diversity (CBD).
• Endangered Species Acts and wildlife protection laws.
• CITES regulating international trade in endangered species.
• Environmental impact assessments before development projects.
• Integration of biodiversity conservation into land-use planning.
• Enforcement mechanisms and penalties for violations.

🌐 EE Focus: An EE could compare the effectiveness of protected areas in two different countries or ecosystems.

📌 Restoration and Sustainable Use

• Reforestation and afforestation projects.
• Wetland restoration to improve water quality and biodiversity.
• Sustainable forestry and fisheries management practices.
• Agroforestry combining agriculture with biodiversity benefits.
• Ecotourism generating revenue while conserving habitats.
• Payment for ecosystem services to incentivise conservation.

❤️ CAS Link: A CAS project could involve volunteering in a local habitat restoration programme or running a biodiversity awareness campaign.

📌 Community and International Collaboration

• Indigenous knowledge integrated into conservation planning.
• Local communities trained as wildlife monitors or eco-guides.
• Cross-border conservation initiatives for migratory species.
• Partnerships between governments, NGOs, and private sector.
• Public awareness campaigns and environmental education.
• Citizen science projects for biodiversity monitoring.

🔍 TOK Perspective: Conservation decisions often involve balancing scientific recommendations with cultural, economic, and political considerations.

📝 Paper 2:
Be prepared to compare in-situ and ex-situ methods, give examples of conservation strategies, and evaluate their effectiveness.

📌Definition Table

Term	Definition
Habitat Loss	The destruction, fragmentation, or degradation of natural habitats, reducing their ability to support species.
Overexploitation	The unsustainable harvesting of species for food, trade, or other purposes.
Invasive Species	Non-native species that outcompete, prey on, or otherwise harm native species and ecosystems.
Pollution	The introduction of harmful substances or energy into the environment, adversely affecting biodiversity.
Climate Change	Long-term alteration of global or regional climate patterns, impacting ecosystems and species survival.

📌Introduction

Biodiversity faces unprecedented threats from human activities, leading to what many scientists call the sixth mass extinction. These threats operate at multiple scales — from local habitat destruction to global climate change — and often act synergistically, accelerating biodiversity loss. Understanding these threats is essential for developing effective conservation strategies and policies to protect life on Earth.

📌 Habitat Loss and Fragmentation

• Caused by agriculture, urbanisation, mining, and infrastructure development.
• Leads to smaller, isolated populations more vulnerable to extinction.
• Reduces available food, shelter, and breeding sites.
• Alters ecological processes such as pollination and nutrient cycling.
• Creates edge effects that change microclimates and species interactions.
• Particularly devastating for species with large home ranges or specialised habitats.

🧠 Examiner Tip: Always specify the driver behind habitat loss in examples — e.g., deforestation for soybean farming in the Amazon.

📌 Overexploitation

• Includes overfishing, overhunting, and overharvesting of plants.
• Depletes populations faster than they can reproduce.
• Can cause collapse of fisheries and wildlife populations.
• Often driven by high market demand and illegal trade.
• Selective harvesting can alter genetic diversity.
• Example: overharvesting of medicinal plants leading to extinction risk.

🧬 IA Tips & Guidance: An IA could assess the impact of human harvesting on population sizes of a local plant or animal species.

📌 Invasive Species

• Outcompete native species for resources.
• May introduce diseases to which natives have no immunity.
• Can alter ecosystem structure and function.
• Often spread through global trade and travel.
• Particularly harmful to island ecosystems.
• Example: introduction of brown tree snakes to Guam leading to bird extinctions.

🌐 EE Focus: An EE could investigate the ecological and economic impacts of a specific invasive species in a local area.

📌 Pollution

• Chemical: pesticides, heavy metals, and industrial waste harming organisms directly.
• Plastic: ingestion and entanglement affecting marine life.
• Nutrient: fertiliser runoff causing eutrophication and dead zones.
• Light and noise: disrupting animal behaviours such as migration and reproduction.
• Pollution can act synergistically with other threats.
• Persistent pollutants can bioaccumulate in food chains.

❤️ CAS Link: A CAS project could involve organising a community clean-up and awareness campaign on pollution impacts on biodiversity.

📌 Climate Change

• Alters temperature and precipitation patterns.
• Shifts species ranges and disrupts migration timing.
• Causes coral bleaching and loss of polar ice habitats.
• Increases frequency of extreme weather events.
• Forces rapid adaptation or migration, which many species cannot achieve.
• Contributes to ocean acidification, harming marine biodiversity.

🔍 TOK Perspective: Decisions on prioritising biodiversity threats involve value judgments, as resources are limited and trade-offs must be made between economic and environmental goals.

📝 Paper 2:
Expect to discuss major threats to biodiversity, give examples, and explain how these threats interact to accelerate species loss.

📌Definition Table

Term	Definition
Biodiversity	The variety of life in all its forms, levels, and combinations, including genetic, species, and ecosystem diversity.
Genetic Diversity	The variation of genes within a species, providing the raw material for adaptation and evolution.
Species Diversity	The number of different species and their relative abundance in an area.
Ecosystem Diversity	The variety of ecosystems and ecological processes within the biosphere.
Endemic Species	Species found only in a specific geographic location.

📌Introduction

Biodiversity is the foundation of ecosystem stability, resilience, and productivity. It is essential for maintaining ecological balance and supporting human well-being through ecosystem services such as food production, water purification, climate regulation, and cultural enrichment. Biodiversity exists at multiple levels — from genetic diversity within species to the variety of ecosystems across landscapes — and is the result of millions of years of evolutionary processes. Its preservation is vital for sustaining life on Earth and adapting to environmental changes.

📌 Levels of Biodiversity

• Genetic diversity ensures populations can adapt to changing environments.
• Species diversity maintains ecosystem balance and resilience.
• Ecosystem diversity supports a wide range of ecological processes.
• All levels are interconnected and influence each other.
• Loss at one level often impacts the others.
• Measurement uses indices such as Shannon-Wiener or Simpson’s index.

🧠 Examiner Tip: When describing biodiversity, always specify the level (genetic, species, or ecosystem) and give an example.

📌 Importance to Ecosystem Functioning

• Enhances ecosystem productivity through niche differentiation.
• Increases stability against environmental fluctuations.
• Supports nutrient cycling and energy flow.
• Provides habitat for a variety of organisms.
• Ensures pollination and seed dispersal.
• Promotes resilience to invasive species and disease outbreaks.

🧬 IA Tips & Guidance: An IA could investigate species diversity in different habitats using a quadrat or transect sampling method.

📌 Importance to Humans

• Provisioning services: food, water, raw materials, medicines.
• Regulating services: climate regulation, flood control, disease regulation.
• Cultural services: recreation, spiritual value, education.
• Supporting services: soil formation, primary production.
• Acts as a genetic resource for crop and livestock improvement.
• Provides economic benefits through tourism and ecosystem products.

🌐 EE Focus: An EE could explore the relationship between biodiversity and crop productivity, analysing how species richness affects yields.

📌 Indicator of Environmental Health

• Healthy ecosystems usually have high biodiversity.
• Sudden biodiversity loss signals environmental degradation.
• Bioindicator species can signal changes in ecosystem quality.
• Monitoring biodiversity helps track climate change impacts.
• Protecting biodiversity protects ecosystem services.
• Restoration ecology aims to recover biodiversity in degraded areas.

❤️ CAS Link: A CAS project could involve organising a biodiversity survey in a local park and presenting results to raise community awareness.

📌 Global Biodiversity Patterns

• Biodiversity is highest in tropical regions and decreases toward the poles.
• Hotspots are regions with high species richness and high threat levels.
• Island ecosystems often have high endemism but are vulnerable to disturbances.
• Mountain regions offer diverse microhabitats increasing species diversity.
• Marine biodiversity is concentrated in coral reefs and coastal zones.
• Climate, geography, and evolutionary history shape biodiversity patterns.

🔍 TOK Perspective: Biodiversity valuation involves subjective decisions about which species and ecosystems are most important, reflecting human perspectives and cultural values.

📝 Paper 2:
Be ready to define biodiversity at different levels, explain its importance to ecosystems and humans, and give examples of biodiversity hotspots.

📌Definition Table

Term	Definition
Adaptive Radiation	The rapid diversification of a single ancestral species into multiple new species, each adapted to a specific ecological niche.
Polyploidy	The condition in which an organism has more than two complete sets of chromosomes, common in plant speciation.
Autopolyploidy	Polyploidy arising from chromosome duplication within a single species.
Allopolyploidy	Polyploidy resulting from hybridisation between different species followed by chromosome doubling.
Niche Differentiation	The process by which competing species use the environment differently to coexist.

📌Introduction

Adaptive radiation is a process where an ancestral species rapidly diversifies into multiple species adapted to different ecological niches. In plants, speciation is often influenced by polyploidy, hybridisation, and environmental variation. Plant adaptive radiation is especially common on islands, in isolated habitats, or following environmental change. The flexibility of plant reproductive systems and their ability to undergo genome duplication allow for rapid formation of reproductively isolated lineages.

📌 Key Features of Adaptive Radiation

• Begins with a single ancestral species colonising new or underused environments.
• Rapid speciation driven by ecological opportunities.
• Morphological and physiological adaptations evolve for specific niches.
• Reduced competition in newly colonised areas accelerates diversification.
• Can occur after mass extinctions or environmental shifts.
• Results in high biodiversity in a relatively short evolutionary period.

🧠 Examiner Tip: When giving examples of adaptive radiation, always link species’ adaptations to the ecological niches they occupy.

📌 Role of Polyploidy in Plant Speciation

• Common in plants but rare in animals.
• Autopolyploidy results from nondisjunction during meiosis, producing unreduced gametes.
• Allopolyploidy combines chromosome sets from different species.
• Polyploid plants are often reproductively isolated from diploid relatives.
• Can lead to immediate speciation in a single generation.
• Examples: bread wheat (Triticum aestivum), cotton, tobacco.

🧬 IA Tips & Guidance: An IA could compare chromosome numbers in related plant species to investigate possible polyploid origins.

📌 Environmental and Ecological Drivers

• Island ecosystems promote rapid radiation due to isolation and diverse habitats.
• Mountain ranges create microhabitats and climatic gradients.
• Human-altered landscapes can generate novel niches.
• Pollinator specialisation drives floral diversification.
• Seasonal and climatic variation influences reproductive timing.
• Soil type and nutrient availability affect plant morphology and physiology.

🌐 EE Focus: An EE could explore the role of pollinator diversity in driving adaptive radiation in flowering plants.

📌 Examples of Adaptive Radiation in Plants

• Hawaiian silverswords: radiated from a single ancestor into diverse forms adapted to different altitudes and habitats.
• Galápagos Scalesia: tree-like daisies adapting to varied island conditions.
• African violets: diversified in mountain forests with distinct niches.
• Wild sunflowers: adapted to different soil types and moisture levels.
• Brassica crops: artificial selection mimicking natural adaptive diversification.
• Orchid family: extreme floral diversity linked to specialised pollinators.

❤️ CAS Link: A CAS activity could involve planting and observing species adapted to different microhabitats in a school garden to illustrate adaptive variation.

📌 Plant Speciation Mechanisms Beyond Polyploidy

• Hybridisation without chromosome doubling can still produce new species.
• Ecological isolation via adaptation to distinct microhabitats.
• Temporal isolation due to differences in flowering periods.
• Gametic incompatibility between pollen and stigma.
• Chromosomal rearrangements reducing fertility with parent species.
• Reinforcement of barriers through selection against hybrids.

🔍 TOK Perspective: Plant speciation challenges the idea that species boundaries are fixed — polyploidy can create new species almost instantly, showing how rapid evolutionary change is possible.

📝 Paper 2:
Expect questions asking you to explain polyploidy, give plant examples of adaptive radiation, and relate environmental factors to speciation rates.

📌Definition Table

Term	Definition
Speciation	The process by which new species arise from existing ones.
Allopatric Speciation	Speciation due to geographical isolation between populations.
Sympatric Speciation	Speciation occurring within the same geographical area, often due to ecological or behavioural isolation.
Reproductive Isolation	Barriers preventing gene flow between populations, leading to speciation.
Hybrid Zone	Region where two species meet and interbreed, producing hybrids.

📌Introduction

Speciation is the formation of new species through the gradual accumulation of genetic differences that prevent interbreeding. This process is driven by reproductive isolation, which can be caused by geographic separation, ecological divergence, behavioural differences, or genetic incompatibility. Understanding isolation mechanisms is crucial for explaining biodiversity patterns and evolutionary processes.

📌 Types of Speciation

• Allopatric: Geographic barriers prevent gene flow, leading to divergence.
• Peripatric: Small populations become isolated at the edge of a larger population’s range, allowing rapid divergence.
• Parapatric: Adjacent populations diverge while maintaining some gene flow.
• Sympatric: Occurs without physical barriers, often via polyploidy in plants or niche specialisation.
• Speciation speed varies — can be gradual or rapid.
• Molecular evidence helps confirm speciation events.

🧠 Examiner Tip: Always link examples of speciation to the type — e.g., Darwin’s finches (allopatric), cichlid fish in the same lake (sympatric).

📌 Prezygotic Isolation Mechanisms

• Temporal isolation: species breed at different times/seasons.
• Behavioural isolation: unique courtship behaviours prevent interbreeding.
• Mechanical isolation: incompatible reproductive structures.
• Ecological isolation: different habitats reduce encounters.
• Gametic isolation: gametes cannot fuse due to chemical incompatibility.
• Prezygotic barriers prevent fertilisation entirely.

🧬 IA Tips & Guidance: A possible IA could investigate mating behaviours in a model organism to study behavioural isolation patterns.

📌 Postzygotic Isolation Mechanisms

• Hybrid inviability: hybrids fail to develop or survive.
• Hybrid sterility: hybrids survive but cannot reproduce (e.g., mule).
• Hybrid breakdown: hybrid offspring viable but less fit or fertile in subsequent generations.
• Postzygotic barriers reinforce species boundaries.
• Often result from genetic incompatibilities.
• Maintain separation even when hybridisation occurs.

🌐 EE Focus: An EE could analyse genetic incompatibilities causing hybrid sterility in closely related species.

📌 Role of Natural Selection and Genetic Drift

• Natural selection drives adaptation to different environments, reinforcing isolation.
• Genetic drift can fix differences in small populations.
• Founder effects accelerate divergence in isolated groups.
• Sexual selection may lead to reproductive isolation through mate preferences.
• Isolation allows accumulation of unique alleles.
• Gene flow reduction is key to speciation.

❤️ CAS Link: A CAS project could involve presenting case studies of local species undergoing isolation to a school science club.

📌 Examples of Speciation in Nature

• Darwin’s finches (allopatric, adaptive radiation).
• Apple maggot flies shifting from hawthorn to apple trees (sympatric).
• Cichlid fishes in African lakes (sympatric).
• Polar and grizzly bears producing hybrids yet remaining distinct species.
• Plant polyploidy in wheat and other crops.
• Squirrels separated by the Grand Canyon (allopatric).

🔍 TOK Perspective: Speciation illustrates how defining species is not always straightforward — the concept is shaped by the criteria scientists choose to emphasise (morphological, genetic, ecological).

📝 Paper 2:
Expect to explain types of speciation, give examples, and distinguish between prezygotic and postzygotic isolation mechanisms.

📌Definition Table

Term	Definition
Evolution	The change in heritable characteristics of populations over successive generations.
Microevolution	Small-scale evolutionary changes within a population over short timescales.
Macroevolution	Large-scale evolutionary changes that result in the formation of new species or higher taxa.
Fossil Record	Preserved remains or traces of past organisms, providing evidence of evolutionary change.
Homologous Structures	Structures with similar anatomy due to shared ancestry, even if function differs.

📌Introduction

Evolution explains the diversity of life by showing how species change over time through natural selection and other mechanisms. Evidence for evolution comes from multiple disciplines, including palaeontology, comparative anatomy, embryology, molecular biology, and biogeography. The integration of fossil evidence with genetic data has created a robust framework that connects extinct and extant species in a continuous evolutionary lineage.

📌 Fossil Evidence

• Shows chronological changes in organisms through the geological record.
• Transitional fossils bridge gaps between major groups (e.g., Archaeopteryx between reptiles and birds).
• Radiometric dating provides accurate age estimates for fossils.
• Fossil distribution aligns with evolutionary theory and plate tectonics.
• Reveals extinct species and their relationship to modern organisms.
• Helps calibrate molecular clocks for evolutionary timelines.

🧠 Examiner Tip: When giving fossil examples, always link them to the evolutionary transition they represent.

📌 Anatomical and Embryological Evidence

• Homologous structures indicate shared ancestry (e.g., vertebrate forelimbs).
• Analogous structures arise from convergent evolution, not shared ancestry.
• Vestigial structures are remnants of features from ancestors (e.g., human appendix).
• Comparative embryology shows similar developmental stages among different species.
• Morphological patterns can be mapped onto phylogenetic trees.
• Anatomy supports hypotheses generated from molecular data.

🧬 IA Tips & Guidance: An IA could compare morphological data from related species to test phylogenetic predictions.

📌 Molecular Evidence

• DNA and protein sequence comparisons show degrees of relatedness.
• Highly conserved genes (e.g., cytochrome c) provide deep evolutionary links.
• Molecular clocks estimate divergence times.
• Supports and refines phylogenetic trees built from morphology.
• Can reveal cryptic species undetectable by anatomy alone.
• Mitochondrial DNA useful for tracing maternal lineages.

🌐 EE Focus: An EE could investigate the correlation between genetic similarity and geographical distribution of related species.

📌 Biogeographical Evidence

• Species distribution patterns support continental drift and plate tectonics.
• Endemic species on islands often resemble mainland relatives but are distinct.
• Adaptive radiation seen in isolated habitats (e.g., Darwin’s finches).
• Continental separation explains unique fauna in Australia.
• Dispersal and vicariance shape species ranges.
• Fossil distribution matches predicted historical land connections.

❤️ CAS Link: A CAS project could involve mapping local biodiversity and explaining its evolutionary significance to a community audience.

📌 Observations of Evolution in Action

• Antibiotic resistance in bacteria evolves rapidly under selection pressure.
• Insecticide resistance in agricultural pests.
• Industrial melanism in peppered moths as an example of natural selection.
• Climate change affecting migration and breeding times in birds.
• Laboratory experiments demonstrating artificial selection in plants/animals.
• Rapid evolution in invasive species adapting to new environments.

🔍 TOK Perspective: The variety of evidence for evolution highlights the role of converging lines of inquiry in building strong scientific theories.

📝 Paper 2:
Be prepared to describe multiple lines of evidence for evolution, give examples, and explain how different data sources complement each other.

📌Definition Table

Term	Definition
Reclassification	The reassignment of organisms to different taxonomic groups based on new evidence.
Systematics	The scientific study of the diversity of organisms and their evolutionary relationships.
Monophyletic Group	A group containing an ancestor and all its descendants.
Polyphyletic Group	A group containing organisms from different ancestors, not including their most recent common ancestor.
Paraphyletic Group	A group containing an ancestor and some, but not all, of its descendants.

📌Introduction

Reclassification is an essential part of taxonomy as scientific understanding evolves. As new evidence emerges — particularly from molecular genetics — organisms may be reassigned to more accurate groups. This process reflects the dynamic nature of systematics, which aims to represent evolutionary history as precisely as possible. Reclassification ensures that taxonomic systems remain consistent with current scientific knowledge, even if it means overturning long-held classifications.

📌 Reasons for Reclassification

• Discovery of new fossil or living species.
• Molecular evidence (DNA, RNA, protein sequences) revealing unexpected relationships.
• Correction of historical misclassifications based on superficial similarities.
• Evidence of convergent evolution misleading earlier classification.
• Advances in bioinformatics allowing more robust phylogenetic analysis.
• Refinement of evolutionary models to reflect new data.

🧠 Examiner Tip: When discussing reclassification in IB answers, always give a concrete example, such as the reclassification of prokaryotes into separate domains: Bacteria and Archaea.

📌 Impact of Molecular Evidence

• DNA sequencing can reveal genetic similarities and differences invisible to morphology.
• Ribosomal RNA gene sequences are often used to determine deep evolutionary splits.
• Mitochondrial DNA is used for recent divergence studies.
• Molecular data can confirm or contradict morphology-based classifications.
• Has led to major taxonomic revisions, such as splitting Protista into multiple lineages.
• Supports the three-domain system over the traditional five-kingdom model.

🧬 IA Tips & Guidance: A possible IA could analyse genetic sequence data from online databases to propose a reclassification of a selected group.

📌 Examples of Reclassification

• Prokaryotes: Once grouped as Monera, now divided into Bacteria and Archaea.
• Fungi: Previously classified with plants, now recognised as a separate kingdom.
• Whales: Once grouped separately, now classified with even-toed ungulates (Artiodactyla) based on molecular data.
• Protists: Split into multiple eukaryotic supergroups based on genetic evidence.
• Pandas: Giant pandas and red pandas once thought closely related, now placed in different families.
• Birds: Reclassified as a subgroup of reptiles based on cladistic analysis.

🌐 EE Focus: An EE could examine the role of molecular evidence in the reclassification of a specific taxonomic group, integrating both historical and modern perspectives.

📌 Challenges in Reclassification

• Requires consensus among the scientific community.
• Can cause confusion in literature and field guides.
• Changes in names may affect conservation legislation and legal documents.
• Requires updates to educational materials and databases.
• Some classifications remain debated despite molecular evidence.
• Historical inertia can slow adoption of new classifications.

❤️ CAS Link: A CAS project could involve updating a local biodiversity database to reflect recent taxonomic changes.

📌 Role of Systematics in Modern Biology

• Integrates taxonomy, evolutionary biology, and molecular genetics.
• Informs conservation priorities by identifying evolutionarily distinct species.
• Supports ecological studies by clarifying species identities.
• Assists in tracking the spread of invasive species.
• Helps in drug discovery by identifying related species with known properties.
• Contributes to understanding the tree of life.

🔍 TOK Perspective: Reclassification illustrates how scientific knowledge is provisional and subject to revision — even well-established systems can change when new evidence arises.

📝 Paper 2:
Expect questions asking you to explain why reclassification occurs, give examples, and discuss how molecular evidence has reshaped taxonomy.

📌Definition Table

Term	Definition
Cladistics	A method of classification that groups organisms based on common ancestry and shared derived characteristics (synapomorphies).
Clade	A group of organisms consisting of a common ancestor and all its descendants.
Synapomorphy	A shared derived trait unique to a clade, indicating common ancestry.
Node	A branching point on a cladogram representing the most recent common ancestor of the descendant lineages.
Outgroup	A species or group outside the clade being studied, used to infer ancestral traits.

📌Introduction

Cladistics is a classification approach that focuses on evolutionary relationships rather than overall similarity. It groups organisms into clades, each representing a single branch of the tree of life, defined by shared derived characteristics. Cladograms, the diagrams produced through cladistic analysis, visually represent hypotheses about evolutionary relationships. This method has transformed taxonomy, particularly with the integration of molecular data, making it possible to resolve relationships that morphology alone could not.

📌 Principles of Cladistics

• Groups are based solely on shared derived traits, not ancestral traits.
• All members of a clade share a common ancestor.
• Cladograms are constructed using both morphological and molecular data.
• Branching order represents hypothesised evolutionary pathways.
• Outgroups help determine which traits are ancestral vs derived.
• Cladistics aims for monophyletic groups — including all descendants of a common ancestor.

🧠 Examiner Tip: When drawing cladograms, label each branch with a shared derived characteristic; avoid mixing ancestral traits with synapomorphies.

📌 Construction of Cladograms

• Identify traits and determine which are ancestral vs derived.
• Use an outgroup for reference.
• Assign traits to different branches based on appearance in evolutionary history.
• Arrange branches so that each node represents the emergence of a new trait.
• Molecular data (DNA, RNA, protein sequences) can refine branch placement.
• Branch length may or may not represent evolutionary time — check diagram details.

🧬 IA Tips & Guidance: A possible IA could construct cladograms from genetic sequence data of related plant or animal species and compare them to morphology-based diagrams.

📌 Advantages of Cladistics

• Reflects actual evolutionary history more accurately than traditional systems.
• Allows integration of molecular evidence.
• Avoids polyphyletic and paraphyletic groupings.
• Highlights the evolutionary significance of traits.
• Can be updated easily with new data.
• Provides testable hypotheses about relationships.

🌐 EE Focus: An EE could investigate whether morphological or molecular data produce more accurate cladograms for a specific taxonomic group.

📌 Limitations of Cladistics

• Requires accurate identification of derived vs ancestral traits.
• Convergent evolution can mislead trait-based analysis.
• Incomplete fossil records may limit available data.
• Different data sets (morphological vs molecular) can produce conflicting trees.
• Rapid evolutionary change can obscure relationships.
• Assumes traits evolve in a linear, non-reversible fashion (which may not be true).

❤️ CAS Link: A CAS project could involve teaching younger students how to read and construct cladograms through an interactive workshop.

📌 Molecular Cladistics

• Uses DNA, RNA, or protein sequence comparisons to identify similarities and differences.
• Molecular clocks estimate divergence times between clades.
• Ribosomal RNA sequences are often used due to their slow rate of change.
• Mitochondrial DNA is useful for tracing maternal lineages.
• Data analysis requires bioinformatics tools.
• Can reveal cryptic evolutionary relationships invisible to morphological study.

🔍 TOK Perspective: Cladistics shows how scientific knowledge is shaped by the choice of evidence — morphological and molecular data may lead to different interpretations of evolutionary history.

📝 Paper 2:
Be ready to draw and interpret cladograms, define key terms (clade, synapomorphy), and compare molecular vs morphological evidence in cladistics.