IB Biology: a subject that feels bigger than your timetable
There’s a moment every IB student recognises: you open your notes to “cells” and somehow end up in ecosystems, gene expression, and a graph you swear is judging you. That’s IB Biology in a nutshell. It’s not just content to memorise. It’s a way of thinking across scales, from molecules to ecosystems, and then proving you can apply that thinking under exam pressure.
This complete guide to IB Biology breaks down what the course is, how the 2025-onward syllabus is organised, how assessment works, and how to revise with less panic and more precision.
Quick checklist: what you need to know about IB Biology
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IB Biology is a Group 4 science in the IB Diploma Programme.
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The 2025 syllabus is organised around four themes used across four levels of biological organisation.
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Both SL and HL cover the same core foundation, but HL goes deeper and adds extra content.
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Assessment is mainly external exams (80%) plus the Internal Assessment (IA) (20%).
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The 2025 syllabus removes option content and Paper 3.
If you want one home base for the course, start with the IB Biology resource hub and keep it open as your map.
What is IB Biology?
IB Biology explores living systems, their structures, and the processes that keep them stable, and sometimes change them entirely. You study everything from enzymes and membranes to population dynamics and evolution, but the goal isn’t to collect facts. The goal is to explain patterns in living things using evidence.
A helpful way to think about IB Biology is as a spiral. You revisit the same big ideas repeatedly, but each time with a wider lens: molecules, cells, organisms, and ecosystems. If your revision feels scattered, it’s often because you’re studying topics as isolated chapters instead of connected systems.
To see how RevisionDojo structures those connections, explore the IB Biology lessons for Theme A (Unity and Diversity).
IB Biology curriculum structure (2025 syllabus)
The 2025-onward IB Biology syllabus is built around four themes:
Theme A: Unity and Diversity
Life looks different everywhere, yet shares a common biochemical foundation. This theme links classification, evolution, and molecular evidence.
Theme B: Form and Function
Structures exist because they work. From membranes to muscles, you connect anatomy and physiology to survival.
Theme C: Interaction and Interdependence
Biology is rarely “one cause, one effect.” You study feedback loops, systems, and emergent properties in cells and ecosystems.
Theme D: Continuity and Change
What stays stable (homeostasis) and what shifts (inheritance, evolution) shapes everything from gene pools to health.
You’ll feel these themes showing up again and again in IB Biology exam questions, especially when you’re asked to apply knowledge to unfamiliar data.
Core topics you’ll meet in IB Biology (SL and HL)
All students build a foundation across:
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Cell biology (structure, membranes, transport, origins of cells, viruses)
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Molecular biology (biomolecules, enzymes and metabolism, DNA/RNA basics, photosynthesis and respiration)
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Genetics (inheritance, meiosis, genetic technologies)
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Ecology (energy flow, populations, biodiversity)
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Evolution and biodiversity (mechanisms, evidence, classification)
If you want topic-specific support, RevisionDojo’s Notes make this manageable. For example, you can review cell structure quickly using A2.2 Cell structure notes or tighten your evolution explanations with Evidence for evolution notes.
HL-only content: what gets added (and why it feels heavier)
HL IB Biology doesn’t just add more pages. It adds more depth: mechanisms, evaluation, and multi-step reasoning. HL students meet topics such as:
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Muscle and motility
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Chemical and neural signalling
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Gene expression mechanisms
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Virus structure and classification
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Cladistics and deeper classification reasoning
The difference shows up in how questions are written. HL expects you to explain “how” and “why,” not just “what.” That’s where targeted practice helps, like drilling topic questions in RevisionDojo’s Questionbank.
Practical work and the IA in IB Biology
Practical work is part of the identity of IB Biology:
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SL: about 40 hours of practical work
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HL: about 60 hours of practical work
Your Internal Assessment (IA) is one investigation that counts for 20% of your grade, with around 10 hours allocated for both SL and HL. The IA rewards clear thinking more than flashy equipment: a focused research question, controlled variables, clean processing, and honest evaluation.
If you want models for what “good” looks like, RevisionDojo’s Coursework Library and Grading tools help you compare your write-up against rubric expectations and tighten weaknesses early.
Assessment structure for IB Biology (2025-onward)
The new assessment structure is simpler than older versions:
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External exams: 80%
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Paper 1: multiple-choice and data questions (about 1.5-2 hours)
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Paper 2: short and extended response (about 1.5-2.5 hours)
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IA: 20%
Remember: the 2025 syllabus removes option content and Paper 3, so your time is best spent mastering the core themes, data handling, and explanation skills.
For exam strategy specifically, this guide is worth a read: How to Pass IB Biology SL Exams: Proven Study Strategy.
How to revise IB Biology without drowning in content
Most students don’t struggle because IB Biology is “too hard.” They struggle because revision becomes passive.
Here’s a simple loop that works:
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Learn with clear explanations (RevisionDojo Study Notes and Lessons)
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Recall with spaced practice (RevisionDojo Flashcards)
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Apply with exam-style practice (RevisionDojo Questionbank, plus AI Chat feedback)
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Simulate with timed practice (RevisionDojo Mock Exams and Predicted Papers)
To build a more visual overview before drills, try IB Biology Cheatsheets. Then sharpen one subtopic at a time, for example, by practising D1.1 DNA replication or tackling an application-heavy area like photosynthesis through targeted practice.
Closing: make IB Biology feel smaller by making it structured
The secret to thriving in IB Biology isn’t superhuman motivation. It’s reducing chaos. Once you see the four themes repeating across molecules, cells, organisms, and ecosystems, the course stops feeling like random chapters and starts feeling like one connected story.
If you want that structure in one place, RevisionDojo brings it together with Study Notes, Flashcards, Questionbank, AI Chat, Grading tools, Predicted Papers, Mock Exams, Coursework Library, and Tutors, so your next practice session actually moves your score.
Explore the full IB Biology toolkit here: IB Biology Resources.