IB Biology Syllabus Guide 2026: SL and HL Topic Breakdown for Singapore Students
IB Biology Syllabus Guide 2026: SL and HL Topic Breakdown for Singapore Students
Study guide/
Complete IB Biology SL and HL syllabus breakdown for 2026 - topic structure, assessment weights, IA requirements, and comparison with H2 Biology 9477 for Singapore students.
IB Biology (first assessment 2025) uses a concept-based approach built around four unifying themes rather than a list of numbered topics. The Internal Assessment - a personal scientific investigation - is worth 20 % of the final grade at both SL and HL. Singapore students at ACS(I) and SJI commonly sit IB Biology alongside peers in JCs studying H2 Biology 9477, and the two curricula differ more than many students expect.
Quick IB Biology Map
The core idea is simple: IB Biology is organised by concepts, not old numbered topics.
Use it as a working check: SL and HL share the same themes, but HL adds more depth and the IA still counts for 20% of the grade.
Then go one layer deeper: Study by linking levels of biology: molecules, cells, organisms, populations, and ecosystems. That is how many IB questions are framed.
IB Biology syllabus structure (post-2025 reform)
The redesigned IB Biology curriculum replaces the previous topic-numbered structure with four unifying concepts that run across all content areas. These concepts are not separate modules to be studied in isolation - they are lenses through which all biological content is interpreted and examined.
Unity and diversity
This concept covers the shared molecular and cellular basis of life alongside the extraordinary variety of life forms. Content includes:
Cell biology - cell theory, prokaryotic and eukaryotic cell structure, membrane structure and transport
Molecular biology - DNA structure and replication, transcription, translation, proteins and enzymes
Classification and phylogenetics - taxonomy, cladistics, evidence for evolutionary relationships
Students are expected to connect molecular-level explanations (gene expression) to organism-level diversity (phenotypic variation). Exam questions frequently require moving between scales - from nucleotide to organism to population.
Form and function
This concept examines how the structure of biological systems relates to their function across plant and animal physiology. Key areas include:
Human physiology - digestion, gas exchange, transport (heart, blood vessels, lymph), immune responses, kidney and osmoregulation, hormonal and nervous coordination, reproduction
Plant biology - structure of leaves, roots and stems, transport in xylem and phloem, photosynthesis, reproduction in flowering plants
Exchange surfaces - adaptations for efficient exchange of gases, nutrients, and waste
HL students study additional depth in human physiology, including the biochemistry of muscle contraction, the detailed mechanics of nerve impulse transmission, and plant hormones. Many Singapore students find this section familiar from O-Level Biology but underestimate the molecular depth expected at HL.
Interaction and interdependence
This concept covers relationships between organisms and between organisms and their environment. Content spans:
Ecology - ecosystems, food webs, energy flow, nutrient cycles (carbon, nitrogen), population dynamics
Human impact - biodiversity loss, invasive species, climate change effects on ecosystems, conservation strategies
IB Biology places considerably more emphasis on ecology and conservation than H2 Biology 9477. Fieldwork experience informs the IA for many students choosing ecology-based investigations. Evolution is treated as a unifying principle throughout all four concepts rather than a standalone topic.
Continuity and change
This concept addresses how biological information is passed through generations and how it changes over time. Key areas include:
Inheritance - Mendelian genetics, sex linkage, codominance, multiple alleles, chi-squared test
At HL, this concept includes more detailed treatment of gene regulation and epigenetics, connecting molecular mechanisms to evolutionary and developmental outcomes.
SL vs HL: what changes
Both SL and HL students study the same four unifying concepts, but the scope, depth, and assessment demands differ substantially.
Feature
SL
HL
Recommended teaching hours
~150 h
~240 h
Additional HL content
None
~90 h of extension material
Assessment hours (external)
~3.5 h total across papers
~5.5 h total across papers
Internal Assessment
20 % (shared requirement)
20 % (shared requirement)
IA word count
~3 000 words
~3 000 words
Depth of molecular biology
Moderate
High (gene regulation, epigenetics)
Depth of human physiology
Core systems
Core + detailed biochemistry
Evolution coverage
Natural selection, speciation
+ Hardy-Weinberg, population genetics
Ecological modelling
Qualitative
Quantitative (productivity, efficiency)
The additional HL hours are not spent on entirely new topics. Instead, HL students revisit SL content at a deeper level and study extension material that connects the four concepts - for example, the molecular basis of hormonal signalling or the quantitative treatment of population genetics. This means HL exam questions can blend multiple concepts in a single extended-response item.
Assessment structure
IB Biology is assessed through two or three written examination papers (depending on level) and the Internal Assessment.
Component
SL
HL
What it tests
Paper 1A - MCQ
30 questions, 45 min
40 questions, 1 h
Recall, comprehension, data interpretation
Paper 1B - data-based
Short answers, 45 min
Short answers, 1 h
Data analysis, graph reading, evaluation
Paper 2 - extended
1.25 h
2.25 h
Structured and extended-response questions
Internal Assessment
20 %, ~10 h lab work
20 %, ~10 h lab work
Personal scientific investigation
External total
80 %
80 %
Papers 1A, 1B, 2
IA total
20 %
20 %
Independent investigation write-up
Paper 2 carries the highest marks for both levels. Extended-response questions require students to synthesise content from across the four unifying concepts and to evaluate experimental design and data. Many Singapore students under-prepare for these longer-form questions, which demand structured scientific writing rather than bullet-point answers.
Topic-by-topic breakdown
Cell biology and molecular biology (Unity and diversity)
Teaching hours: approximately 30–40 h (SL), 45–55 h (HL).
Core concepts: cell theory, membrane structure (fluid mosaic model), active and passive transport, enzyme kinetics (Michaelis-Menten at HL), DNA structure and replication (semi-conservative), transcription and translation, gene mutation, protein structure and function.
Genetics and inheritance (Unity and diversity / Continuity and change)
Teaching hours: approximately 20–30 h (SL), 30–40 h (HL).
Core concepts: Mendelian ratios, sex linkage, codominance, epistasis (HL), chi-squared analysis, meiosis and its role in variation, gene regulation (operons at HL).
Exam question types: Punnett square problems, chi-squared calculation and interpretation, extended analysis of inheritance patterns from family pedigrees.
Ecology and evolution (Interaction and interdependence / Continuity and change)
Teaching hours: approximately 25–35 h (SL), 35–45 h (HL).
Exam question types: process description, ethical evaluation, application to novel biotechnology scenarios.
IA requirements
The Internal Assessment is a personal scientific investigation worth 20 % of the final grade. It is teacher-assessed and externally moderated by the IB. Both SL and HL students submit the same type of investigation - there is no separate HL IA requirement.
Criterion
Marks
What is assessed
Personal engagement
2
Genuine ownership, initiative, reflection
Exploration
6
Research question, background, methodology
Analysis
6
Data processing, statistical treatment
Evaluation
6
Conclusion, sources of error, improvement
Communication
4
Structure, scientific writing, presentation
Total
24
Converted to a percentage score
The write-up should be approximately 6–12 pages (roughly 3 000 words). Figures, tables, and raw data appendices do not count toward the word limit.
Popular Biology IA topics from Singapore students:
Enzyme kinetics investigations are consistently popular and well-suited to school lab equipment. Examples include exploring the effect of substrate concentration on catalase activity (using hydrogen peroxide decomposition), or measuring the effect of pH on amylase activity using colorimetric methods.
Plant biology investigations are manageable with grow-lights and simple measurement tools. Examples include the effect of light colour on the rate of photosynthesis in aquatic plants (Elodea), or the effect of salt concentration on transpiration rate using a potometer.
Microbiology investigations can be high-scoring but require careful biosafety planning. Examples include antibiotic disc diffusion assays (zones of inhibition), the effect of temperature on yeast fermentation rate, or comparing bacterial growth on different growth media.
Common IA mistakes:
Choosing a research question that is too broad to investigate within 10 hours
Collecting fewer than five data points per condition, making statistical analysis unreliable
Omitting standard deviation or another measure of uncertainty from the analysis
Writing the evaluation as a list of errors without proposing specific, actionable improvements
Ignoring the personal engagement criterion, which rewards explaining why the topic matters to you
IB Biology vs H2 Biology (9477): key differences
Singapore students choosing between IB and A-Level pathways often ask how Biology compares across the two systems. The content overlap is substantial - both cover cell biology, genetics, physiology, and ecology - but the emphasis and assessment style differ meaningfully.
Feature
IB Biology
H2 Biology (9477)
Syllabus organisation
Four unifying concepts (cross-cutting)
Numbered topics (modular)
Ecology depth
Strong - dedicated concept, fieldwork link
Lighter - covered but not emphasised
Molecular biology depth
Moderate at SL; high at HL
High throughout - central to 9477
Evolution coverage
Integrated across all four concepts
Present but more contained
Practical assessment
IA (20 %, independent investigation)
Practical exam (20 %, timed school-based)
Assessment style
Data-based questions, extended response
Structured questions, essay-type
Grading scale
1–7
A–U (Cambridge grade)
IA / coursework component
Yes - sustained investigation over weeks
No - timed practical exam only
Biotechnology emphasis
Moderate (ethics explicitly assessed)
Moderate (technical focus)
Biochemistry depth
Moderate
High (Krebs cycle, ETC in detail)
Where IB Biology goes further: ecology and conservation (stronger ecosystem modelling, biodiversity ethics), evolution as a cross-cutting theme, the personal investigation IA, and ethical evaluation of biotechnology.
Where H2 Biology goes further: molecular biology (detailed biochemistry - the Krebs cycle, electron transport chain, detailed enzyme mechanism), cellular respiration mechanisms, and structured problem-solving under timed conditions.
Study strategy for Singapore IB students
Context: ACS(I) and SJI pathways
Most Singapore students taking IB Biology come from ACS(I) (Anglo-Chinese School Independent) or SJI (St Joseph's Institution), both of which offer the full IB Diploma. These schools have experienced Biology teachers and internal specimen papers, but students often compare themselves to JC peers sitting H2 Biology - an understandable anxiety that does not always map correctly to IB assessment demands.
Lean into ecology and evolution
IB Biology's stronger emphasis on ecology and evolution is an opportunity, not a burden. These sections reward students who read widely and engage with current scientific debates (biodiversity loss, climate change impacts, rewilding). The personal engagement criterion in the IA also benefits from genuine ecological curiosity. If you find molecular biology less engaging, building strength in ecology and evolution can meaningfully support your Paper 2 extended-response marks.
Master the data-based questions early
Paper 1B tests data interpretation skills that are different from content recall. Practise reading and interpreting unfamiliar graphs, tables, and experimental results from the first term of your IB course - not just in the revision period. The IB publishes specimen papers for the new curriculum, and old Paper 3 questions from the previous format are useful for data-practice even if the structure has changed.
Use H2 Biology resources for molecular depth
If you find the molecular biology and biochemistry sections of IB HL Biology challenging, H2 Biology 9477 resources go deeper in this area and can supplement your understanding. Past H2 Biology papers have excellent structured questions on enzyme kinetics, DNA replication, and cell signalling that translate directly to IB HL content. See IB Subject Planning for Singapore Universities for guidance on how IB subject choices interact with university prerequisites.
Plan your IA topic in Year 1
The IA accounts for 20 % of your grade and takes several weeks of sustained work. Students who leave topic selection to Year 2 consistently produce weaker IAs. In Year 1, identify two or three possible investigation areas, discuss feasibility with your teacher, and run a short pilot to check that your dependent variable is measurable with available equipment. See Internal Assessments for the International Baccalaureate for a full IA planning guide.
Treat extended-response writing as a skill to train
Paper 2 extended-response questions are often worth 8–10 marks and require structured, paragraph-form answers that integrate concepts across the four unifying themes. Many students lose marks not because they lack knowledge but because their answers lack structure. Practise answering with a clear claim, biological mechanism, and connection to evidence in every extended-response paragraph.
For students considering the IB Extended Essay in Biology, see the IB Extended Essay STEM Research Design Playbook for guidance on framing a research question and structuring the investigation.
The difficulty depends on your strengths. H2 Biology 9477 demands greater molecular and biochemical depth - the detailed biochemistry of respiration and complex enzyme kinetics are tested more rigorously. IB Biology at HL demands stronger data analysis skills, sustained IA work, and the ability to write extended-response answers integrating multiple concepts. Students who prefer essay-style thinking and independent research often find IB Biology more suited to their strengths; students who prefer structured content mastery and timed problem-solving may find H2 Biology more tractable. Neither is objectively harder - they test different skills.
What are good IA topics for Biology?
The strongest IA topics are measurable, original, and personally motivated. Reliable categories include enzyme kinetics (effect of a variable on enzyme activity, using a simple colorimetric assay), plant biology (photosynthesis rate, transpiration rate, seed germination), and microbiology (bacterial growth assays, fermentation experiments). Avoid topics requiring equipment your school does not have, or investigations that depend on results from a single trial. The evaluation criterion rewards honest discussion of limitations - so simple designs with clear limitations often score better than ambitious designs with uncontrolled variables.
Do NUS and NTU accept IB Biology for medicine prerequisites?
Both NUS Yong Soo Lin School of Medicine and NTU Lee Kong Chian School of Medicine list Biology as a prerequisite (or strongly recommended subject) for admission. IB Biology HL is accepted by both institutions in lieu of H2 Biology. Some programmes specify a minimum grade - typically 5 or above at HL. Check the specific programme requirements directly, as prerequisites can change between admission cycles. Refer to IB Subject Planning for Singapore Universities for a current summary of IB subject acceptance across NUS, NTU, SMU, and SUTD.
Should I take Biology at HL or SL?
Take Biology at HL if: you are applying for medicine, dentistry, pharmacy, nursing, or life sciences programmes at Singapore or overseas universities; you find biological sciences genuinely engaging at depth; or you want the IA to serve as preparation for a science-focused Extended Essay or university research. Take Biology at SL if: Biology is a supporting subject for a non-biological science or social science course; you need HL hours for Mathematics, Chemistry, or Physics; or you are meeting a breadth requirement rather than a specialist pathway. Students aiming for medicine should confirm HL Biology is required or preferred before dropping to SL - most Singapore medical schools expect HL.
Status: IB Biology subject guide (first assessment 2025) checked 2026-03-28. Four-concept structure, two-paper external exam model (Papers 1A, 1B, 2), and 20 % IA weighting confirmed for May 2026 session.
