# IB Biology Syllabus (Latest) – Core Topics, HL Topics and Optional Units

> IB Biology Syllabus with Core, Higher Level (HL) and optional topics arranged by units and lessons to help students understand the complete course structure.

Canonical URL: https://biologynotesonline.com/ib-biology-syllabus/
Author: Sourav Pan
Last updated: September 30, 2026

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The IB Biology Syllabus provides a structured outline of the biological concepts and topics studied in the International Baccalaureate Diploma Programme. It includes major areas such as cell biology, molecular biology, genetics, ecology, evolution, human physiology, plant biology and animal physiology.

This page organizes the syllabus into Core topics, Additional Higher Level (AHL) topics and optional units, with individual lessons listed under each section. Short descriptions are also included to explain the main concepts covered in each lesson.

Students can use this syllabus outline to identify important topics, organize their Biology notes and understand how different areas of the course are arranged.

## I. Cell Biology

- [Introduction to Cells](https://biologynotesonline.com/cell-structure-characteristics-types-size-and-shape-functions/)
Covers cell theory, characteristics of unicellular organisms, limits on cell size, cell differentiation and the role of stem cells in development and medicine.

- [Ultrastructure of Cells](https://biologynotesonline.com/cell-organelles-structure-and-their-functions/)
Examines the internal organization of prokaryotic and eukaryotic cells, major cellular structures and the use of light and electron microscopy to study cells.

- [Membrane Structure](https://biologynotesonline.com/fluid-mosaic-model-of-plasma-membrane/)
Explains the phospholipid bilayer, membrane proteins, cholesterol and the fluid mosaic model used to describe the organization of biological membranes.

- [Membrane Transport](https://biologynotesonline.com/mode-of-transport-across-plasma-membrane/)
Covers movement of substances across membranes through diffusion, facilitated diffusion, osmosis and active transport, together with endocytosis and exocytosis.

- [The Origin of Cells](https://biologynotesonline.com/cell-structure-characteristics-types-size-and-shape-functions/)
Examines the principle that cells arise from existing cells, possible origins of the first cells and the endosymbiotic explanation for the evolution of eukaryotic cells.

- [Cell Division](https://biologynotesonline.com/cell-division-definition-types-mitosis-meiosis-cell-cycle/)
Covers the cell cycle, mitosis, chromosome condensation, cytokinesis, regulation by cyclins and the relationship between uncontrolled cell division and tumour formation.

## II. Molecular Biology

- [Molecules to Metabolism](https://biologynotesonline.com/biological-macromolecules-types-structure-functions-examples/)
Introduces metabolism as the complete set of chemical reactions occurring in cells and examines the importance of carbon-based compounds in living organisms.

- [Water](https://biologynotesonline.com/structure-of-water-and-hydrogen-bonding/)
Explores the polarity and hydrogen bonding of water and explains how its thermal, cohesive and solvent properties make it essential for living systems.

- [Carbohydrates and Lipids](https://biologynotesonline.com/biological-macromolecules-types-structure-functions-examples/)
Covers the structures and functions of major carbohydrates and lipids, including their roles in energy storage, energy supply and cellular organization.

- [Proteins](https://biologynotesonline.com/proteins/)
Examines amino acids, peptide formation and the different levels of protein structure, together with the wide variety of functions performed by proteins.

- [Enzymes](https://biologynotesonline.com/enzymes/)
Explains enzyme-substrate interactions and investigates how temperature, pH and substrate concentration influence enzyme activity, including the use of immobilized enzymes.

- [Structure of DNA and RNA](https://biologynotesonline.com/biological-macromolecules-types-structure-functions-examples/)
Covers the nucleotide structure of DNA and RNA, complementary base pairing and the arrangement of nucleotides within these nucleic acids.

- [DNA Replication, Transcription and Translation](https://biologynotesonline.com/dna-replication-steps/)
Examines how DNA is copied and how genetic information is transcribed into RNA and translated into an amino acid sequence during protein synthesis.

- [Cell Respiration](https://biologynotesonline.com/cellular-respiration-equation/)
Introduces the release of usable energy from organic compounds through cellular respiration, including aerobic and anaerobic pathways.

- [Photosynthesis](https://biologynotesonline.com/photosynthesis/)
Covers the conversion of light energy into chemical energy, the role of chlorophyll and factors that affect the rate of photosynthesis.

## III. Genetics

- Genes
Introduces genes as heritable DNA sequences and examines loci, alleles, genome organization and differences in genome size among organisms.

- [Chromosomes](https://biologynotesonline.com/chromosome/)
Covers chromosome structure and number, homologous chromosomes, sex chromosomes, karyograms and the relationship between chromosomes and genes.

- [Meiosis](https://biologynotesonline.com/meiosis/)
Explains reduction division, homologous chromosome separation, crossing over and independent assortment and how these processes generate genetic variation.

- [Inheritance](https://biologynotesonline.com/mendels-laws-of-inheritance/)
Covers alleles, genotypes, phenotypes, dominant and recessive inheritance, genetic crosses, sex-linked inheritance and pedigree analysis.

- [Genetic Modification and Biotechnology](https://biologynotesonline.com/genetic-engineering/)
Examines techniques used to analyse and manipulate DNA, including PCR, gel electrophoresis, DNA profiling, gene transfer and genetically modified organisms.

## IV. Ecology

- [Species, Communities and Ecosystems](https://biologynotesonline.com/structure-and-function-of-ecosystems/)
Introduces species, populations, communities and ecosystems and examines relationships between organisms and their biotic and abiotic environments.

- [Energy Flow](https://biologynotesonline.com/energy-flow-in-ecosystem/)
Explains how energy enters ecosystems, moves through food chains and trophic levels and is progressively lost from biological systems.

- [Carbon Cycling](https://biologynotesonline.com/carbon-cycle/)
Covers the movement of carbon between organisms, the atmosphere, oceans, soil and fossil carbon stores through biological and geological processes.

- Climate Change
Examines the greenhouse effect, greenhouse gases and links between increasing atmospheric carbon dioxide, global temperature and environmental change.

## V. Evolution and Biodiversity

- [Evidence for Evolution](https://biologynotesonline.com/common-ancestry-definition-theory-evidence/)
Examines evidence supporting evolution, including selective breeding, homologous structures, fossil evidence and patterns of variation between populations.

- [Natural Selection](https://biologynotesonline.com/natural-selection-definition-theory-types-examples/)
Explains how variation, competition, differential survival and reproduction can change the characteristics of populations over generations.

- [Classification of Biodiversity
](https://biologynotesonline.com/biodiversity/)Covers biological classification, binomial nomenclature, taxonomic groups and characteristics used to classify major groups of living organisms.

- [Cladistics](https://biologynotesonline.com/biometrics-numerical-taxonomy-and-cladistics/)
Introduces cladograms and explains how shared characteristics and molecular evidence can be used to infer evolutionary relationships.

## VI. Human Physiology

- [Digestion and Absorption](https://biologynotesonline.com/mechanical-and-chemical-digestion-of-food-absorptions-of-differenet-molecules/)
Covers digestion of food, actions of digestive enzymes and absorption of digested nutrients through the specialized surface of the small intestine.

- [The Blood System](https://biologynotesonline.com/human-circulatory-system/)
Examines the structure and function of the heart, blood vessels and circulation and explains how blood transports substances around the body.

- [Defence Against Infectious Disease](https://biologynotesonline.com/innate-immunity/)
Covers barriers against pathogens, blood clotting, antibody responses and the use of antibiotics in controlling bacterial infections.

- [Gas Exchange
](https://biologynotesonline.com/physiology-of-respiration-respiratory-system-breathing-gas-exchange-mechanism-regulation/)Examines ventilation of the lungs, the structure of alveoli and the adaptations that allow efficient exchange of oxygen and carbon dioxide.

- [Neurons](https://biologynotesonline.com/nervous-system/) and [Synapses](https://biologynotesonline.com/synapse-definition-parts-types-function/)
Covers nerve impulses, membrane potentials, transmission along neurons and communication between neurons across synapses.

- [Hormones, Homeostasis and Reproduction](https://biologynotesonline.com/homeostasis/)
Examines hormonal regulation, blood glucose control, thermoregulation and hormonal control of human reproductive processes.

## Additional Higher Level (AHL) Syllabus

### VII. Nucleic Acids

- [DNA Structure and Replication](https://biologynotesonline.com/dna-replication-steps/)
Examines DNA structure in greater molecular detail, including nucleosomes, DNA supercoiling and the enzymes and mechanisms involved in DNA replication.

- [Transcription and Gene Expression](https://biologynotesonline.com/transcription/)
Covers transcription in greater depth and examines how gene expression can be regulated, including modification of RNA and control of transcription.

- [Translation](https://biologynotesonline.com/protein-synthesis-translation-definition-steps-sites-machinery/)
Examines the molecular events of translation, including tRNA, ribosomes, codons and the processes of initiation, elongation and termination of polypeptide synthesis.

### VIII. Metabolism, Cell Respiration and Photosynthesis

- Metabolism
Examines metabolic pathways, enzyme regulation and the ways enzymes control interconnected sequences of biochemical reactions.

- [Cell Respiration](https://biologynotesonline.com/cellular-respiration-equation/)
Covers glycolysis, the link reaction, Krebs cycle, electron transport and oxidative phosphorylation involved in aerobic ATP production.

- [Photosynthesis](https://biologynotesonline.com/photosynthesis/)
Examines light-dependent reactions, photophosphorylation and the Calvin cycle involved in converting light energy into organic molecules.

### IX. Plant Biology

- [Transport in the Xylem of Plants](https://biologynotesonline.com/nutrient-transport-mechanism-in-plants/)
Explains water uptake and movement through plants, including transpiration, cohesion of water and the structural adaptations of xylem vessels.

- [Transport in the Phloem of Plants](https://biologynotesonline.com/translocation-in-phloem-structure-phloem-loading-and-unloading/)
Covers translocation of organic compounds from sources to sinks and the mechanisms involved in loading and transporting substances through phloem tissue.

- Growth in Plants
Examines plant growth through cell division and elongation, the role of meristems and the effects of plant hormones such as auxin.

- [Reproduction in Plants](https://biologynotesonline.com/modes-of-reproduction-and-pollination-in-crop-plants/)
Covers flowering, pollination, fertilization, seed formation and environmental factors involved in flowering and germination.

### X. Genetics and Evolution

- [Meiosis](https://biologynotesonline.com/meiosis/)
Examines meiosis in greater detail, including chromosome behaviour, crossing over, recombination and mechanisms responsible for generating genetic diversity.

- [Inheritance](https://biologynotesonline.com/mendels-laws-of-inheritance/)
Extends genetic analysis to dihybrid crosses, gene linkage, recombination and more complex patterns of inheritance.

- [Gene Pools and Speciation](https://biologynotesonline.com/gene-pool-definition-types-working-importance-evolution-examples/)
Covers allele frequencies within populations and examines how reproductive isolation, selection and other evolutionary processes can lead to the formation of new species.

### XI. Animal Physiology

- [Antibody Production and Vaccination](https://biologynotesonline.com/vaccines-definition-development-mechanism-types-examples-side-effects/)
Examines specific immune responses, activation of lymphocytes, antibody production, memory cells, vaccination and the development of immunity.

- [Movement](https://biologynotesonline.com/muscle-types-structure-development-functions/)
Covers the structure of skeletal muscle, interactions between actin and myosin and the sliding-filament mechanism responsible for muscle contraction.

- [The Kidney and Osmoregulation](https://biologynotesonline.com/kidney-structure-anatomy-urine-formation-acid-base-balance-and-function/)
Examines nephron structure, ultrafiltration, selective reabsorption and hormonal control of water balance by the kidneys.

- [Sexual Reproduction](https://biologynotesonline.com/sexual-reproduction-stages-types-advantages-examples/)
Covers reproductive anatomy, spermatogenesis, oogenesis, fertilization, pregnancy and hormonal regulation of reproductive processes.

## Optional Topics

### XII. Neurobiology and Behaviour

#### Core Lessons

- Neural Development
Examines development of the nervous system, formation of neural connections and changes in neuronal connections during growth and learning.

- [The Human Brain](https://biologynotesonline.com/human-brain-definition-structure-characteristics-functions/)
Covers major regions of the brain, their functions and methods used to investigate brain activity and neurological function.

- [Perception of Stimuli](https://biologynotesonline.com/sensory-receptors-definition-types-mechanism-functions/)
Examines sensory receptors and neural processing involved in detecting and interpreting environmental stimuli.

#### Additional Higher Level Lessons

- [Innate and Learned Behaviour](https://biologynotesonline.com/mechanisms-of-behaviour/)
Compares genetically influenced behaviours with behaviours acquired through experience and examines mechanisms involved in learning.

- Neuropharmacology
Examines how drugs and other chemicals affect synaptic transmission, nervous-system function and behaviour.

- [Ethology](https://biologynotesonline.com/mechanisms-of-behaviour/)
Covers the biological study of animal behaviour and examines how natural selection can influence behavioural patterns.

### XIII. Biotechnology and Bioinformatics

#### Core Lessons

- Microbiology: Organisms in Industry
Examines the use of microorganisms in industrial processes and the conditions required for controlled microbial growth and production.

- [Biotechnology in Agriculture](https://biologynotesonline.com/applications-of-biotechnology/)
Covers biological technologies used in agriculture, including manipulation of organisms and techniques used to improve agricultural production.

- [Environmental Protection](https://biologynotesonline.com/applications-of-biotechnology/)
Examines applications of microorganisms and biotechnology in waste treatment, pollution control and environmental management.

#### Additional Higher Level Lessons

- [Medicine](https://biologynotesonline.com/applications-of-biotechnology/)
Explores biotechnology used in medical diagnosis, treatment and production of biologically important therapeutic substances.

- [Bioinformatics](https://biologynotesonline.com/bioinformatics/)
Covers computer-based storage and analysis of biological information, particularly DNA and protein sequence data.

### XIV. Ecology and Conservation

#### Core Lessons

- [Species and Communities](https://biologynotesonline.com/structure-and-function-of-ecosystems/)
Examines ecological niches, interactions between species and factors affecting the distribution and abundance of organisms.

- [Communities and Ecosystems](https://biologynotesonline.com/structure-and-function-of-ecosystems/)
Covers energy flow, productivity and interactions among organisms and environmental components within ecosystems.

- [Impacts of Humans on Ecosystems
](https://biologynotesonline.com/disruptions-to-ecosystems-causes-consequences-preventions/#human-impacts-on-ecosystems)Examines pollution and other human activities that alter ecosystem structure, functioning and environmental quality.

- [Conservation of Biodiversity
](https://biologynotesonline.com/biodiversity/#biodiversity-conservation)Covers causes of biodiversity loss and examines strategies used to protect species, habitats and biological diversity.

#### Additional Higher Level Lessons

- [Population Ecology
](https://biologynotesonline.com/population/)Examines changes in population size, growth patterns and environmental factors that regulate populations.

- [Nitrogen Cycle](https://biologynotesonline.com/nitrogen-cycle-steps-and-significance/) and [Phosphorus Cycles](https://biologynotesonline.com/phosphorus-cycle/)
Covers movement and transformation of nitrogen and phosphorus through ecosystems and the roles of organisms in these nutrient cycles.

### XV. Human Physiology

#### Core Lessons

- Human Nutrition
Examines the nutritional requirements of humans, including essential nutrients, energy requirements and effects of dietary imbalance.

- [Digestion](https://biologynotesonline.com/mechanical-and-chemical-digestion-of-food-absorptions-of-differenet-molecules/)
Covers mechanical and chemical digestion and the roles of digestive organs, enzymes and secretions in breaking down food.

- Functions of the Liver
Examines the liver's roles in metabolism, nutrient processing, detoxification, storage and regulation of substances in the blood.

- [The Heart](https://biologynotesonline.com/human-circulatory-system/)
Covers cardiac structure, the cardiac cycle, electrical control of heartbeat and mechanisms responsible for pumping blood.

#### Additional Higher Level Lessons

- [Hormones and Metabolism](https://biologynotesonline.com/homeostasis/)
Examines endocrine regulation of metabolism and the physiological effects of hormones involved in maintaining metabolic balance.

- Transport of Respiratory Gases
Covers the transport of oxygen and carbon dioxide in blood, haemoglobin function and factors affecting oxygen loading and unloading.

## Disclaimer

Disclaimer: The IB Biology Syllabus information provided on this page is presented for educational and reference purposes only. Biology Notes Online is not affiliated with, endorsed by, or officially associated with the International Baccalaureate Organization (IB). The syllabus topics have been independently organized and described based on educational source material and are not intended to reproduce the original publication. Official curriculum requirements and examination information should always be confirmed through authorized IB resources. For any copyright-related concern regarding material on this page, please contact Biology Notes Online through our website OR please email us at  - biologynotesonlinecontact@gmail.com

## References

- International Baccalaureate Organization. (n.d.). Biology – Diploma Programme. [https://www.ibo.org/programmes/diploma-programme/curriculum/sciences/biology/](https://www.ibo.org/programmes/diploma-programme/curriculum/sciences/biology/)

- International Baccalaureate Organization. (2022). Biology SL and HL subject brief: First assessment 2025. [https://www.ibo.org/globalassets/new-structure/recognition/pdfs/dp_sciences_biology_subject-brief_jan_2022_e.pdf](https://www.ibo.org/globalassets/new-structure/recognition/pdfs/dp_sciences_biology_subject-brief_jan_2022_e.pdf)

- International Baccalaureate Organization. (n.d.). Sciences – Diploma Programme. [https://www.ibo.org/programmes/diploma-programme/curriculum/sciences/](https://www.ibo.org/programmes/diploma-programme/curriculum/sciences/)

- International Baccalaureate Organization. (n.d.). Diploma Programme curriculum. [https://www.ibo.org/programmes/diploma-programme/curriculum/](https://www.ibo.org/programmes/diploma-programme/curriculum/)

- International Baccalaureate Organization. (n.d.). DP professional development learning resources. [https://www.ibo.org/professional-development/free-learning/dp-pd-learning-resources/dp-nano-resources/](https://www.ibo.org/professional-development/free-learning/dp-pd-learning-resources/dp-nano-resources/)

- International Baccalaureate Organization. (n.d.). Assessment and exams – Diploma Programme. [https://www.ibo.org/programmes/diploma-programme/assessment-and-exams/](https://www.ibo.org/programmes/diploma-programme/assessment-and-exams/)

- International Baccalaureate Organization. (2025). Diploma Programme examination instructions – Biology. [https://ibpublishing.ibo.org/exinst/apps/exinst/index.html?chapter=1&doc=EX_instructions_2025_e&part=11](https://ibpublishing.ibo.org/exinst/apps/exinst/index.html?chapter=1&doc=EX_instructions_2025_e&part=11)