HL IB Biology Revision Notes 2025

Syllabus Edition

First teaching 2023

First exams 2025

Unity & Diversity

Hydrogen Bonds

Physical & Chemical Properties of Water

Origin of Water on Earth (HL)

DNA & RNA Structure

Basis of Genetic Code

Nucleic Acid Structure & Function

DNA Structure (HL)

Nucleosomes & Molecular Visualisation Software: Skills (HL)

The Hershey & Chase Experiment (HL)

Chargaff's Data (HL)

Formation of Carbon Compounds (HL)

Evolution of Cells (HL)

Evidence for Evolution of Life (HL)

Cell Theory

Cell Theory: Skills

Microscopes

General Cell Structure

Prokaryotic Cell Structure

Eukaryotic Cell Structure

Functions of Life

Eukaryotic Cell Structure: Comparisons & Atypical Examples

Cell Types & Structures: Skills

Drawing Cells: Skills

Endosymbiotic Theory (HL)

Cell Differentiation (HL)

Multicellularity (HL)

Virus Structure (HL)

Replication in Viruses (HL)

Origin & Evolution of Viruses (HL)

Biological Species Concept

Chromosome Number

Karyograms: Skills

Genomes

Comparing Genome Sizes: Skills

Uses of Genome Sequencing

Biological Species Concept: Challenges (HL)

Chromosome Number: Cross-Breeding (HL)

Dichotomous Keys: Skills (HL)

Environmental DNA & Barcodes (HL)

Biological Classification (HL)

Cladistics (HL)

Reclassification (HL)

Classification System (HL)

Evolution

Evidence of Evolution

Convergent Evolution

Speciation

Types of Speciation (HL)

Adaptive Radiation (HL)

Speciation in Plants (HL)

Biodiversity

Reasons for Extinction

Ecosystem Loss

Loss of Biodiversity

How to Preserve Biodiversity

Form & Function

Properties of Carbon

Macromolecules

Carbohydrates: Definition, Functions & Examples

Role of Glycoproteins

Lipids

Fatty Acids

Phospholipids

Formation of Proteins

The Variety of Proteins

Protein Structure: Effect of pH & Temperature

Amino Acid Diversity (HL)

Levels of Protein Structure (HL)

Globular & Fibrous Proteins (HL)

Lipid Bilayers

Membrane Proteins

Membrane Transport

Glycolipids & Glycoproteins

The Fluid Mosaic Model: Skills

Membrane Fluidity (HL)

Active Transport & Bulk Transport (HL)

Cell Adhesion (HL)

Cell Organelles

Cell Compartmentalisation

Adaptations of Mitochondria & Chloroplasts (HL)

Organelles in Protein Synthesis (HL)

Vesicle Formation (HL)

Stem Cells

Cell Specialisation

Specialised Cells (HL)

Examples of Specialised Cells (HL)

Gas Exchange in Organisms

Mammalian Lungs: Adaptations

Mechanism of Ventilation

Measuring Lung Volumes: Skills

Gas Exchange in Plants

Drawing Leaf Structure: Skills

Determining Stomatal Density: Skills

Haemoglobin & Oxygen (HL)

The Bohr Shift (HL)

The Oxygen Dissociation Curve (HL)

Blood Vessels

Identify Blood Vessels: Skills

Measuring Pulse Rate: Skills

Coronary Heart Disease: Skills

The Transpiration Stream

Adaptations of Xylem Vessels

Drawing Root & Stem Structure: Skills

Tissue Fluid (HL)

Circulatory Systems (HL)

The Mammalian Heart (HL)

The Cardiac Cycle: Skills (HL)

The Roots & Water Transport (HL)

Translocation in Plants (HL)

Adaptations for Movement (HL)

Mechanism of Muscle Contraction (HL)

Skeletal Muscle (HL)

Requirements for Movement (HL)

Movement of Joints: Skills (HL)

Locomotion in Organisms (HL)

Habitats

Abiotic Factors & Species Distribution

Species Distribution: Skills

Abiotic Factors: Marine & Terrestrial

Biomes

Ecological Niches

Methods of Nutrition

Nutrition in Hominidae: Skills

Nutrition: Adaptations of Organisms

Competition Between Species

Interaction & Interdependence

Metabolism: Enzymes & Reactions

Enzyme Action

Enzyme Activity: Skills

Enzyme Reaction Rates: Skills

Activation Energy: Skills

Metabolic Pathways (HL)

Enzyme Inhibition (HL)

Adenosine Triphosphate (ATP)

Cell Respiration

Cell Respiration: Skills

Oxidation & Reduction (HL)

Glycolysis (HL)

Anaerobic Respiration (HL)

The Link Reaction & The Krebs Cycle (HL)

Oxidative Phosphorylation (HL)

Respiratory Substrates (HL)

The Process of Photosynthesis

Separating Photosynthetic Pigments: Skills

Absorption Spectra

Absorption & Action Spectra: Skills

Limiting Factors of Photosynthesis: Skills

Carbon Dioxide Enrichment Experiments

Photosystems (HL)

Light Dependent Reactions (HL)

Photophosphorylation (HL)

Light Independent Reactions (HL)

Interdependence of Photosynthetic Reactions (HL)

Cell Signalling (HL)

Signalling Molecules (HL)

Receiving the Signal (HL)

Transmembrane Receptors (HL)

Epinephrine Receptors (HL)

Intracellular Receptors (HL)

Regulating Cell Signalling (HL)

Neurones: Function & Structure

Nerve Impulses

Nerve Impulses: Skills

Synapses

Action Potentials (HL)

Interpreting Oscilloscope Traces: Skills (HL)

Nerve Conduction Velocity (HL)

Synaptic Transmission (HL)

Neurones in the Brain (HL)

Integration in Living Organisms

The Nervous System

Reflex Arc & Movement Control

Epinephrine & Melatonin

Control Mechanisms

Observing Tropic Responses: Skills (HL)

Phototropism (HL)

Plant Hormones (HL)

Regulating Plant Growth & Fruit Ripening (HL)

Pathogens

Barriers to Pathogens: Skin & Mucous Membranes

Blood Clotting

The Immune System

White Blood Cells

Adaptive Immune Response

HIV & AIDS

Antibiotics

Antibiotic Resistance

Zoonoses

Vaccines & Immunity

Evaluating COVID-19 Data: Skills

Populations in Ecosystems

Estimating Population Size

Limiting Population Size

Limiting Population Size: Examples

Population Growth Curves: Skills

Populations: Intraspecific Relationships

Community: Interspecific Relationships

Interspecific Competition

Chi-Squared Test: Skills

Ecosystems as Open Systems

Energy Flow in Ecosystems

Obtaining Carbon Compounds in Ecosystems

Trophic Levels

Pyramids of Energy: Skills

Energy Losses

Primary & Secondary Production

The Carbon Cycle

Nutrient Cycling

Continuity & Change

DNA Replication

Electrophoresis & PCR

Electrophoresis & PCR: Applications

Mechanism of DNA Replication (HL)

Transcription in Protein Synthesis

Translation in Protein Synthesis

The Genetic Code

Protein Structure & Mutations

Mechanism of Transcription (HL)

Post-Transcriptional Modification (HL)

Translation & the Proteome (HL)

Gene Mutations

Consequences of Gene Mutations

Mutations & Genetic Variation

Gene Editing (HL)

Conserved Sequences (HL)

Uncontrolled Cell Division & Tumour Formation (HL)

Mitotic Index: Skills (HL)

Gene Expression (HL)

Regulating Transcription & Translation (HL)

Environment & Gene Expression (HL)

Environment & Gene Expression: Examples (HL)

Water Movement in Plant Tissue (HL)

Sexual & Asexual Reproduction

Seed Dispersal & Germination

Hormones & Puberty (HL)

Gametogenesis (HL)

Fertilisation & Implantation (HL)

Hormones in Pregnancy (HL)

The Placenta (HL)

Hormone Replacement Therapy (HL)

Genetic Inheritance & Genetic Crossing

Inheritance: Terminology

Inheriting Alleles

Sex Determination

Pedigree Charts

Continuous Variation: Skills

Dihybrid Crosses & Unlinked Genes (HL)

Statistical Analysis of Dihybrid Crosses (HL)

Genes & Polypeptides: Skills (HL)

Gene Linkage (HL)

Identifying Recombinants (HL)

Homeostasis: Maintaining the Internal Environment

Regulation of Blood Glucose

Thermoregulation

Osmoregulation & Excretion (HL)

Production of Urine (HL)

Changes in Blood Supply to Organs (HL)

Natural Selection & Evolution

Selection Pressures

Selection Pressures: Skills

Gene Pools (HL)

Allele Frequencies: Skills (HL)

Types of Natural Selection (HL)

Hardy-Weinberg Principle (HL)

Artificial Selection (HL)

Stability in Ecosystems

Ecosystem Stability: Skills

Keystone Species

Sustainability in Ecosystems & Agriculture

Eutrophication

The Effects of Pollution

Restoring Ecosystems

Ecological Succession (HL)

Human Influence on Succession (HL)

Causes of Climate Change

Impact of Climate Change

Carbon Sequestration

Climate Change: Phenology (HL)

Climate Change: Evolution (HL)

Tools

Safety, Ethical & Environmental Issues in Biology

Measuring Variables in Biology

Applying Techniques in Biology

Applying Technology to Collect Data in Biology

Applying Technology to Process Data in Biology

Applying General Mathematics in Biology

Using Units, Symbols & Numerical Values in Biology

Processing Uncertainties in Biology

Graphing in Biology

Study tools