IB DEMYSTIFIED

Examiners . Moderators . Authors

Menu
Book Meeting
🧬
IB Biology›Biology HL
Revision Notes

IB Biology HL

Clear, student-friendly revision notes for IB Biology Higher Level — every SL theme plus the HL depth (viruses, classification, muscle & movement, chemical signalling, gene expression and more), each with worked examples and exam pointers for Papers 1 and 2.

Biology HL · Revision Notes

Table of Contents

Click any topic to expand and view all the notes inside.

1

Life’s Building Blocks & Variety

Water, DNA, cells, viruses, the diversity of life, classification, evolution and conservation.

55 notes▾

Water & Its Properties

3▾
Hydrogen Bonds→ Water’s Physical & Chemical Properties→ Origin of Water on Earth→

DNA, RNA & the Genetic Code

7▾
Structure of DNA & RNA→ The Basis of the Genetic Code→ Nucleic Acid Structure & Function→ DNA Structure→ Nucleosomes & Visualisation Software (Skills)→ The Hershey-Chase Experiment→ Chargaff’s Data→

The Origin of Cells

3▾
Formation of Carbon Compounds→ The Evolution of Cells→ Evidence for the Evolution of Life→

Cell Structure & Microscopy

13▾
Cell Theory→ Cell Theory (Skills)→ Microscopes→ General Cell Structure→ Prokaryotic Cell Structure→ Eukaryotic Cell Structure→ Functions of Life→ Eukaryotic Cells: Comparisons & Atypical Examples→ Cell Types & Structures (Skills)→ Drawing Cells (Skills)→ Endosymbiotic Theory→ Cell Differentiation→ Multicellularity→

Viruses

3▾
Virus Structure→ Replication in Viruses→ Origin & Evolution of Viruses→

Classifying Living Diversity

10▾
The Biological Species Concept→ Chromosome Number→ Karyograms (Skills)→ Genomes→ Comparing Genome Sizes (Skills)→ Uses of Genome Sequencing→ Species Concept: Challenges→ Chromosome Number: Cross-Breeding→ Dichotomous Keys (Skills)→ Environmental DNA & Barcoding→

Classification & Cladistics

4▾
Biological Classification→ Cladistics→ Reclassification→ Classification System→

Evolution & Speciation

7▾
Evolution→ Evidence for Evolution→ Convergent Evolution→ Speciation→ Types of Speciation→ Adaptive Radiation→ Speciation in Plants→

Protecting Biodiversity

5▾
Biodiversity→ Causes of Extinction→ Ecosystem Loss→ Loss of Biodiversity→ Preserving Biodiversity→
2

Structure & Function in Living Things

The molecules and structures of life — membranes, organelles, gas exchange, transport, muscle and adaptation.

69 notes▾

Carbohydrates & Lipids

7▾
Properties of Carbon→ Macromolecules→ Carbohydrates: Function & Examples→ The Role of Glycoproteins→ Lipids→ Fatty Acids→ Phospholipids→

Proteins & Their Structure

6▾
How Proteins Form→ The Variety of Proteins→ Protein Structure: pH & Temperature→ Amino Acid Diversity→ Levels of Protein Structure→ Globular & Fibrous Proteins→

Cell Membranes & Transport

8▾
Lipid Bilayers→ Membrane Proteins→ Membrane Transport→ Glycolipids & Glycoproteins→ The Fluid Mosaic Model (Skills)→ Membrane Fluidity→ Active & Bulk Transport→ Cell Adhesion→

Organelles & Compartments

5▾
Cell Organelles→ Cell Compartmentalisation→ Mitochondria & Chloroplast Adaptations→ Organelles in Protein Synthesis→ Vesicle Formation→

Specialised Cells & Stem Cells

4▾
Stem Cells→ Cell Specialisation→ Specialised Cells→ Examples of Specialised Cells→

Gas Exchange Systems

10▾
Gas Exchange in Organisms→ Adaptations of Mammalian Lungs→ How Ventilation Works→ Measuring Lung Volumes (Skills)→ Gas Exchange in Plants→ Drawing Leaf Structure (Skills)→ Determining Stomatal Density (Skills)→ Haemoglobin & Oxygen→ The Bohr Shift→ The Oxygen Dissociation Curve→

Transport in Animals & Plants

13▾
Blood Vessels→ Identifying Blood Vessels (Skills)→ Measuring Pulse Rate (Skills)→ Coronary Heart Disease (Skills)→ The Transpiration Stream→ Xylem Vessel Adaptations→ Drawing Root & Stem Structure (Skills)→ Tissue Fluid→ Circulatory Systems→ The Mammalian Heart→ The Cardiac Cycle (Skills)→ Roots & Water Uptake→ Translocation in Plants→

Muscle & Movement

6▾
Adaptations for Movement→ How Muscles Contract→ Skeletal Muscle→ Requirements for Movement→ Movement of Joints (Skills)→ Locomotion in Organisms→

Adapting to the Environment

5▾
Habitats→ Abiotic Factors & Distribution→ Species Distribution (Skills)→ Abiotic Factors: Marine & Terrestrial→ Biomes→

Ecological Niches & Nutrition

5▾
Ecological Niches→ Methods of Nutrition→ Nutrition in Hominidae (Skills)→ Nutritional Adaptations→ Competition Between Species→
3

Interactions & Ecosystems

How life processes connect — enzymes, energy, signalling, immunity and ecosystems.

82 notes▾

Enzymes & Metabolism

7▾
Metabolism: Enzymes & Reactions→ How Enzymes Work→ Enzyme Activity (Skills)→ Enzyme Reaction Rates (Skills)→ Activation Energy (Skills)→ Metabolic Pathways→ Enzyme Inhibition→

Cellular Respiration

9▾
Adenosine Triphosphate (ATP)→ Cell Respiration→ Cell Respiration (Skills)→ Oxidation & Reduction→ Glycolysis→ Anaerobic Respiration→ The Link Reaction & Krebs Cycle→ Oxidative Phosphorylation→ Respiratory Substrates→

Photosynthesis

11▾
The Process of Photosynthesis→ Separating Photosynthetic Pigments (Skills)→ Absorption Spectra→ Absorption & Action Spectra (Skills)→ Limiting Factors of Photosynthesis (Skills)→ CO₂ Enrichment Experiments→ Photosystems→ Light-Dependent Reactions→ Photophosphorylation→ Light-Independent Reactions→ Interdependent Photosynthetic Reactions→

Chemical Signalling

7▾
Cell Signalling→ Signalling Molecules→ Receiving the Signal→ Transmembrane Receptors→ Epinephrine Receptors→ Intracellular Receptors→ Regulating Cell Signalling→

Nerves & Signalling

9▾
Neurones: Structure & Function→ Nerve Impulses→ Nerve Impulses (Skills)→ Synapses→ Action Potentials→ Interpreting Oscilloscope Traces (Skills)→ Nerve Conduction Velocity→ Synaptic Transmission→ Neurones in the Brain→

Coordinating Body Systems

9▾
Integration in Living Organisms→ The Nervous System→ Reflex Arcs & Movement Control→ Epinephrine & Melatonin→ Control Mechanisms→ Observing Tropic Responses (Skills)→ Phototropism→ Plant Hormones→ Plant Growth & Fruit Ripening→

Disease & Immunity

12▾
Pathogens→ Pathogen Barriers: Skin & Mucous Membranes→ Blood Clotting→ The Immune System→ White Blood Cells→ The Adaptive Immune Response→ HIV & AIDS→ Antibiotics→ Antibiotic Resistance→ Zoonoses→ Vaccines & Immunity→ Evaluating COVID-19 Data (Skills)→

Populations & Communities

9▾
Populations in Ecosystems→ Estimating Population Size→ What Limits Population Size→ Limiting Population Size: Examples→ Population Growth Curves (Skills)→ Intraspecific Relationships→ Interspecific Relationships→ Interspecific Competition→ Chi-Squared Test (Skills)→

Energy & Matter in Ecosystems

9▾
Ecosystems as Open Systems→ Energy Flow in Ecosystems→ Obtaining Carbon Compounds→ Trophic Levels→ Pyramids of Energy (Skills)→ Energy Losses→ Primary & Secondary Production→ The Carbon Cycle→ Nutrient Cycling→
4

Genetics, Inheritance & Change

Passing on life — replication, protein synthesis, division, gene expression, inheritance and balance.

85 notes▾

Replicating DNA

4▾
DNA Replication→ Electrophoresis & PCR→ Electrophoresis & PCR: Applications→ The Mechanism of DNA Replication→

Making Proteins

7▾
Transcription→ Translation→ The Genetic Code→ Protein Structure & Mutations→ The Mechanism of Transcription→ Post-Transcriptional Modification→ Translation & the Proteome→

Mutations & Gene Editing

5▾
Gene Mutations→ Consequences of Mutations→ Mutations & Genetic Variation→ Gene Editing→ Conserved Sequences→

Cell & Nuclear Division

8▾
Cell Division→ Nuclear Division→ Mitosis→ Mitosis (Skills)→ Meiosis→ Cell Cycle→ Uncontrolled Division & Tumours→ Mitotic Index (Skills)→

Gene Expression & Regulation

4▾
Gene Expression→ Regulating Transcription & Translation→ Environment & Gene Expression→ Environment & Gene Expression: Examples→

Osmosis & Water Potential

5▾
Osmosis→ Osmosis in Cells→ Osmosis (Skills)→ Water Potential→ Water Movement in Plant Tissue→

Reproduction

13▾
Sexual & Asexual Reproduction→ Sexual Reproduction→ The Menstrual Cycle→ Fertilisation→ Plant Reproduction→ Pollination→ Seed Dispersal & Germination→ Hormones & Puberty→ Gametogenesis→ Fertilisation & Implantation→ Hormones in Pregnancy→ The Placenta→ Hormone Replacement Therapy→

Genetics & Inheritance

11▾
Genetic Inheritance & Crosses→ Inheritance: Key Terms→ Inheriting Alleles→ Sex Determination→ Pedigree Charts→ Continuous Variation (Skills)→ Dihybrid Crosses & Unlinked Genes→ Statistics of Dihybrid Crosses→ Genes & Polypeptides (Skills)→ Gene Linkage→ Identifying Recombinants→

Homeostasis

6▾
Homeostasis: The Internal Environment→ Blood Glucose Regulation→ Thermoregulation→ Osmoregulation & Excretion→ How Urine is Produced→ Changing Blood Supply to Organs→

Natural Selection

8▾
Natural Selection & Evolution→ Selection Pressures→ Selection Pressures (Skills)→ Gene Pools→ Allele Frequencies (Skills)→ Types of Natural Selection→ Hardy-Weinberg Principle→ Artificial Selection→

Ecosystem Stability & Change

9▾
Stability in Ecosystems→ Ecosystem Stability (Skills)→ Keystone Species→ Sustainable Ecosystems & Agriculture→ Eutrophication→ The Effects of Pollution→ Restoring Ecosystems→ Ecological Succession→ Human Influence on Succession→

Climate Change

5▾
Causes of Climate Change→ Impacts of Climate Change→ Carbon Sequestration→ Climate Change & Phenology→ Climate Change & Evolution→
5

Practical Skills Toolkit

The hands-on methods, tech and maths every biology experiment relies on.

9 notes▾

Skill Set 1: Experimental Technique

3▾
Safety, Ethics & the Environment→ Measuring Variables→ Applying Lab Techniques→

Skill Set 2: Using Technology

2▾
Using Tech to Collect Data→ Using Tech to Process Data→

Skill Set 3: Maths for Biology

4▾
Maths Skills for Biology→ Units, Symbols & Values→ Handling Uncertainties→ Graphing Skills→
6

The Scientific Inquiry Cycle

Working like a scientist, from first question to final evaluation.

8 notes▾

Stage 1: Explore & Design

3▾
Exploring a Problem→ Designing an Investigation→ Controlling Variables→

Stage 2: Collect & Process Data

3▾
Collecting Data→ Processing Data→ Interpreting Results→

Stage 3: Conclude & Evaluate

2▾
Drawing Conclusions→ Evaluating the Method→

Stuck on Biology HL?

Get 1-on-1 tutoring from IB Biology examiners who know exactly what Paper 1 & 2 are looking for.

Book Free Session →

IB Demystified is a trusted online learning platform led by certified IB examiners and educators.

Quick Links

Contact us

  • +44 (0) 7700 1010 59
  • info@ibdemystified.com
  • IB DEMYSTIFIED is UK-registered Pvt Ltd company with Companies House Company Number: 15269948

Follow us

Facebook Tiktok Youtube Linkedin Instagram

© 2026 IB Demystified LTD ALL RIGHTS RESERVED. Powered by AfiaDigital