Revision guide
IB Biology
Command terms, diagram fluency, and turning a content-heavy course into exam marks.
Biology is the most content-dense IB science, organized around four themes — unity and diversity, form and function, interaction and interdependence, and continuity and change. The volume is the challenge: by exam season you're responsible for everything from membrane transport to gene expression to ecosystem dynamics, and cramming it linearly doesn't work. Spaced, active recall — flashcards, blank-page brain dumps, teaching topics aloud — is what makes the volume manageable.
The second challenge is command terms. 'Outline', 'describe', 'explain', and 'discuss' demand different depths, and Biology markschemes award marks per distinct point made. Students who learn to write in markscheme points (short, complete statements, one idea each) reliably outperform students who write flowing paragraphs containing the same knowledge.
How you're assessed
Paper 1 (multiple choice + data)
Multiple choice plus data-based questions on experimental scenarios. The data questions reward calm graph-reading: quote figures, describe trends with numbers, and only then explain the biology.
Paper 2 (extended response)
Short-answer and extended-response questions, including longer essays at HL. Extended responses are marked from a bank of creditable points — plan your answer as a list of points before writing prose.
The IA (Scientific Investigation)
A 20% individual investigation. Biological variability means replicates and statistical treatment matter; an IA with proper sampling, error bars, and a statistical test reads as serious science.
How to revise
Use spaced repetition for the volume
Biology has more discrete facts than any other IB science. Flashcards reviewed on a spaced schedule (the technique built into Baccly's Daily Review) beat re-reading notes by a wide margin.
Draw everything
Mitosis stages, the nephron, the chloroplast, dihybrid crosses: if it can be drawn, exams can ask you to draw or annotate it. Practice diagrams from memory with labels — annotation marks are easy marks.
Answer in markscheme points
For every 'explain' practice question, write numbered points instead of paragraphs, then check how many appear in the markscheme. This habit alone typically adds a grade band on Paper 2.
Master data-response technique
Quote the data ('increases from 12 to 31 arbitrary units between day 2 and day 6'), state the trend, then give the biological reason. All three layers earn marks; most students skip the first.
Mistakes examiners see every year
Writing everything you know instead of answering the command term asked.
Describing a graph without quoting any numbers from it.
Confusing similar processes (mitosis/meiosis, transcription/translation) under time pressure.
Ignoring the HL extension depth — HL questions expect mechanism-level detail.
Choosing an IA question too broad to investigate with controlled variables.
What's in the syllabus
Unity and diversity
Cell theory · Water · Carbohydrates and lipids · Proteins · Membranes and transport · Origins of cells · Cell division
Form and function
Gas exchange · Transport systems · Muscle and movement · Adaptation · Classification · Cladistics
Interaction and interdependence
Enzymes and metabolism · Cell respiration · Photosynthesis · Ecology · Carbon cycling · Population dynamics
Continuity and change
DNA structure · DNA replication · Protein synthesis · Mutation · Inheritance · Evolution · Gene technology
Human physiology
Digestion · Blood glucose control · Immunity · Kidney osmoregulation · Nerves and synapses · Hormones · Reproduction
Frequently asked questions
Is IB Biology just memorization?
Recall is necessary but not sufficient: Papers 1 and 2 both lean on data analysis and application to unfamiliar contexts. The best preparation is recall practice plus a steady diet of data-response questions.
How many hours a week should HL Biology get?
Three to four focused hours outside class keeps the volume under control — ideally as short daily recall sessions rather than a weekly marathon.
Biology or Physics for medicine?
Most medical schools want Chemistry HL plus one more science; Biology is the conventional partner and overlaps heavily with first-year medicine content.
Put this guide into practice
Everything above — topic-filtered practice questions, spaced-repetition flashcards, and a syllabus checklist for Biology — is free on Baccly.
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