Spaced repetition flashcards, daily games, and 1,500+ key terms — covering every topic on the 2025 IB Biology syllabus. Free, forever.
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How it works
Rereading notes is the least effective revision strategy. Cramly uses active recall and spaced repetition — the techniques backed by the most evidence in learning science.
Cards you struggle with come back more often. Cards you know well appear less. The algorithm prioritises exactly what you need to review.
Guess the IB Biology term in 6 tries. A new word every day, drawn from the full syllabus. Great for 5 minutes of active recall on your commute.
Type as many IB Biology keywords as you can before the timer runs out. Each correct term adds 6 seconds. Race the leaderboard.
See exactly which topics you're weakest in, track your daily streak, and watch your mastery score grow across the full syllabus.
Full syllabus coverage
Cramly covers every topic from the 2025 IB Biology syllabus — both SL and HL. Topics marked HL are Higher Level only.
Hydrogen bonding, cohesion, adhesion, specific heat capacity, surface tension and the properties of water as a solvent.
DNA and RNA structure, nucleotides, complementary base pairing, the double helix, replication, transcription, and translation.
The Miller-Urey experiment, protocells, LUCA, the reducing atmosphere, ribozymes, and the origins of life on Earth.
Prokaryotic and eukaryotic cells, organelles, electron microscopy, the cytoskeleton, endosymbiosis, and cell theory.
Viral structure, lytic and lysogenic cycles, HIV, coronavirus, bacteriophages, and the role of viruses in evolution.
Species concepts, karyotypes, dichotomous keys, continuous and discrete variation, speciation, and whole genome sequencing.
Cladograms, parsimony, binomial nomenclature, the domains of life, and how molecular data informs classification.
Darwin and Lamarck, heritable variation, natural selection, allopatric and sympatric speciation, and adaptive radiation.
Species richness, ecosystem diversity, in situ and ex situ conservation, seed banks, rewilding, and the biodiversity crisis.
Monosaccharides, disaccharides, polysaccharides, triglycerides, phospholipids, steroids, condensation and hydrolysis reactions.
Amino acids, primary to quaternary structure, denaturation, fibrous vs globular proteins, haemoglobin, insulin, collagen.
The fluid mosaic model, phospholipid bilayer, diffusion, osmosis, active transport, endocytosis, and exocytosis.
Mitochondria, chloroplasts, the Golgi apparatus, lysosomes, ribosomes, and how compartmentalisation enables metabolism.
Stem cells, differentiation, totipotency, pluripotency, erythrocytes, neurons, epithelial cells, and the stem cell niche.
Lung structure, ventilation, haemoglobin and oxygen affinity, the Bohr shift, stomata, gills, and the oxygen dissociation curve.
The cardiac cycle, blood vessels, lymph, xylem, phloem, transpiration, the pressure-flow hypothesis, and coronary heart disease.
The sliding filament theory, sarcomere structure, actin and myosin, antagonistic muscles, synovial joints, and endoskeletons.
Biomes, abiotic factors, range of tolerance, limiting factors, and adaptations to deserts, tundra, tropical forests, and coral reefs.
Fundamental and realised niches, competitive exclusion, herbivory, predation, saprotrophic nutrition, and mixotrophs.
Active site, induced fit, activation energy, competitive and non-competitive inhibition, feedback inhibition, and immobilised enzymes.
Glycolysis, the link reaction, the Krebs cycle, the electron transport chain, chemiosmosis, ATP synthase, and anaerobic pathways.
Photosystems I and II, the light-dependent reactions, the Calvin cycle, carbon fixation, RuBP, Rubisco, and chromatography.
Hormones, receptors, G-proteins, signal transduction, cyclic AMP, the menstrual cycle, and cell-to-cell communication.
Resting and action potentials, synapses, neurotransmitters, myelination, saltatory conduction, and the effects of drugs on the nervous system.
The reflex arc, the enteric nervous system, plant hormones (auxin, ethylene, cytokinin), circadian rhythms, and the brain.
Innate and adaptive immunity, B and T lymphocytes, antibodies, antigens, vaccines, blood clotting, and antibiotic resistance.
Carrying capacity, sigmoid growth curves, the Lincoln index, interspecific and intraspecific competition, mutualism, and parasitism.
Trophic levels, energy pyramids, the carbon cycle, carbon sources and sinks, decomposers, and the Keeling curve.
Helicase, DNA polymerase, leading and lagging strands, Okazaki fragments, PCR, gel electrophoresis, and DNA profiling.
Transcription, translation, codons, anticodons, tRNA, rRNA, mRNA, splicing, the genetic code, and post-translational modification.
Point mutations, frameshift mutations, mutagens, CRISPR-Cas9, gene knockouts, and the ethics of gene editing.
The cell cycle, mitosis, meiosis, crossing over, non-disjunction, Down syndrome, cyclins, checkpoints, and cancer.
Transcription factors, enhancers, epigenetic tags, methylation, histones, the difference between genotype and phenotype.
Osmosis, water potential, solute potential, pressure potential, plasmolysis, crenation, and turgor pressure in cells.
Spermatogenesis, oogenesis, the menstrual and ovarian cycles, fertilisation, IVF, seed dispersal, and flower structure.
Mendel's laws, Punnett grids, codominance, sex linkage, polygenic inheritance, dihybrid crosses, and chi-square tests.
Blood glucose regulation, thermoregulation, osmoregulation, the kidney and nephron, ADH, insulin, glucagon, and negative feedback.
Allele frequency, Hardy-Weinberg equilibrium, directional, stabilising and disruptive selection, and sexual selection.
Ecological succession, keystone species, biomagnification, eutrophication, microplastics, and tipping points.
The albedo effect, ocean acidification, coral bleaching, permafrost, carbon sequestration, and polar habitat loss.
Key vocabulary
Knowing definitions precisely is essential for IB Biology mark schemes. Here's a sample of the terms covered in Cramly across all topics — the full list has 1,500+.
…and 1,400+ more terms in the full app, with flashcards for every one.
Common questions
Everything students commonly ask about revising for IB Biology.
IB Biology is organised into four overarching themes: Unity and Diversity (A topics — water, nucleic acids, cell structure, viruses, classification, evolution, conservation), Form and Function (B topics — carbohydrates, lipids, proteins, membranes, organelles, gas exchange, transport, muscles), Interaction and Interdependence (C topics — enzymes, respiration, photosynthesis, signalling, immunity, populations, energy transfer), and Continuity and Change (D topics — DNA replication, protein synthesis, mutations, cell division, gene expression, reproduction, inheritance, homeostasis, natural selection, climate change).
HL students study all SL content plus additional topics: A2.1 Origins of Cells, A2.3 Viruses, A3.2 Cladistics, B3.3 Muscles, and C2.1 Chemical Signalling.
IB Biology HL covers all SL content plus additional Higher Level-only topics. HL students study Origins of Cells (how life began, the Miller-Urey experiment), detailed Virus biology, Cladistics and molecular classification, Muscles and the sliding filament theory, and Chemical Signalling including hormone cascades and G-proteins.
HL students also complete approximately 90 additional teaching hours compared to SL, and the HL Paper 3 contains HL-only questions. The HL course is significantly more demanding in terms of content depth and mathematical treatment.
The 2025 IB Biology syllabus includes over 1,500 defined key terms across all topics. In practice, the mark scheme rewards precise use of terminology — for example, writing "partially permeable" rather than "selectively permeable" can affect marks in some questions.
Cramly covers every term from the syllabus, organized by topic, so you can focus your revision on areas where your knowledge is weakest.
The most effective strategies for IB Biology are:
Active recall — test yourself on definitions and concepts rather than rereading notes. Flashcards, past paper questions, and games like Cramly's Recall mode force your brain to retrieve information, which strengthens memory far more than passive revision.
Spaced repetition — review material at increasing intervals (1 day, 3 days, 1 week, 2 weeks). Cramly's flashcard algorithm handles the scheduling automatically.
Past papers — IB Biology mark schemes are precise. Practicing on past papers trains you to use the exact phrasing the examiners expect.
Diagram practice — the examiners frequently ask you to label or draw diagrams (the nephron, the sarcomere, the chloroplast, etc.). Drawing these from memory is one of the best ways to test understanding.
Ideally, start building vocabulary from the beginning of the course — even 10 minutes a day of flashcard practice across the full two years is far more effective than intensive cramming in the final weeks.
If your exams are approaching, prioritise: (1) topics you haven't revised at all, (2) definitions and terminology for mark scheme accuracy, (3) past paper practice for Paper 1 MCQs and Paper 2 structured questions.
Yes — Cramly is completely free. There is no premium tier, no paywall, and no credit card required. All flashcards, games, and progress tracking are available at no cost.
1,500+ key terms. Every syllabus topic. Completely free.
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